Ed. Note: This document collects and formats into a html file the 4 long posts referenced in the Sourdough FAQs discussing the detailed science of sourdough cultures and bread, May 1998. The email addresses are left for identifying the poster but may no longer be valid.

Daniel Wing

5/25/98

Some members of this newsgroup will remember that I have posted some of the content of my correspondence with Michael Ganzle, a German sourdough researcher. He has recently reviewed a proof of a book I have written about masonry ovens and naturally fermented bread, and has commented in detail. Those comments will interest those of you who are interested in the science and technology of sourdoughs. This post and others that follow are for you. If you ARE NOT interested in the subject, stop here, and save yourself from confusion and frustration.

In each section Michael quotes a sentence from the book, and then responds: ------------------------------------

“witness the profusion of instant yeast brands-- while the opposite is true **

I strongly appreciate the notion that the “time equals money equation is not true for sourdough bread or any kind of other fermented foods-- wine, soy sauce, cheese, vinegar, fermented sausage: they usually get better if they are fermented for a long time (the definition of “long varies, though, with the different foods).

“I triple it by mixing it with its weight of water and its weight of flour **

There is a microbiological explanation for the three stage sourdough processes. Microbial growth can be divided in three stages. When the organisms are transferred to a new environment (e.g. by refreshing a sourdough that has been in the refrigerator), they take some time to adapt; no growth occurs (“lag phase). Once the organisms are familiar with the new environment, they start to grow exponentially, meaning one doubling of cell counts in a given time (generation time), so called “log phase. Eventually, the culture will become stationary, i.e. the organism have run out of food, or are inhibited by the metabolic end products. For effective sourdough fermentation, one needs a lot of metabolically active cells. After three or more refreshments, the organisms will reliably start to grow soon after inoculation and will produce enough carbon dioxide. Things are different with yeast dough, though: there simply are so many cells that these have to cough only once to raise the dough. --------------------------------------------

“the time it was inoculated and to the temperature at which it is kept than with the size of the inoculation.] Let's call this the second leaven **

Comment No 1: We’ve been doing quite some work to figure out which factors affect microbial growth in sourdough. I’ve done some work in vitro (which is about to be published: Gänzle et al., Modeling of growth of Lactobacillus sanfranciscensis and Candida milleri in response to process parameters of the sourdough fermentation, Applied and Environmental Microbiology, July 1998); and a colleague of mine, Markus Brandt, has tried to figure out how my “model predictions work out during the actual dough fermentation. Taken together, one can state the following:

A) The optimum temperature for sourdough lactobacilli is 32 - 33°C. At 37°C and 20°C, the generation time is twice as long.

B) At 39 and 15°C, the generation time is four times as long.

C) At 41°C and 4°C, no growth is observed.

For the yeasts, the figures are as follows:

A) 28°C(optimum growth)

B) 32/20 (double generation time)

C) 34/14 (fourfold generation time)

D) 35°C, 8°C: no growth.

So: if several refreshments are done above 32°C, the yeasts will drop out eventually. The optimum pH for lactobacilli is 5.0 - 5.5 (which is the initial pH of a sourdough with 5 - 20% inoculum), the minimum pH for growth is 3.8 (they usually produce acid until pH 3.6 is reached).

Lactic or acetic concentrations don’t affect growth of lactobacilli very much: this is the reason why the buffering capacity of the flour is so important for the organism (a high buffering capacity in high ash flours means that the lactobacilli produce much acid until the critical pH is reached). It also means, that in doughs that are continuously operated with a high inoculum (more than about 30%), you’ll find more yeasts and fewer lactobacilli. Eventually, the lactobacilli flora may change, with more acid tolerant lactobacilli (e.g. L. pontis) prevailing. Such a sourdough is found in the Vollmar and Meuser continuous sourdough fermentation machines (there are 6 operating in Germany, and a diploma candidate in our department characterised the microflora of several of these: as the machine is operated with a 50% inoculum, the pH is never above 4.1 - 4.3, and no L. sanfranciscensis is found in those doughs).

Yeasts are different: they don’t mind the pH at all, but are strongly inhibited by acetic acid, and to a much lesser extend by lactic acid. Increasing salt concentrations inhibit growth of lactobacilli, but yeasts tolerate more salt. No salt is added to the sourdough until the final bread dough, but the dough yield affects the salt concentration: with a low dough yield (little water), the salt (ash) is dissolved in a smaller water volume, and the salt concentration goes up: resulting in a slower fermentation.

So much for the “in vitro theory. Surprisingly, Markus has found most of the predictions to come true when he was looking at the cell counts at different temperature, size of inoculum, salt concentration, and pH in rye dough. The variation of the inoculum size was interesting: If he reduced the inoculum size by 2, he had to wait almost exactly one generation time (one doubling time of the lactobacilli) longer until the dough has reached the same cell counts, pH, titrable acidity, and so on as the dough with the higher inoculum. This was true for inoculum sizes between 1% and 20%: at 50% inoculum, the pH is so low that the lactobacilli don’t really grow well, and at an inoculum size of 0.1%, the pH and/or the oxygen pressure in the dough are so high that the cells have a lag-time (see above) of an hour. Thus, a scanty inoculum means one generation time longer fermentation.

The generation time of L. sanfranciscensis in rye dough at 28°C is a little less than an hour (figures may vary with different strains in different flours, but it’s not much more or less than that), so if the inoculation size is reduced from 20 to 2.5%, it’ll take about three hours more until the dough is ripe. The question is, whether these findings are true for all flours and for all organisms. The strain isolated by Kline and Sugihara does not differ very much from the two strains I’ve been looking at. All the literature available tells me that - as long as we’re looking at sourdoughs with a tradition of continuous propagation - the system behaves the same way. Differences may be between rye flour and white wheat flour: in white wheat flour, the enzyme activities are so low that the organisms may run out of food before the critical pH (lactobacilli) or the critical acetic acid concentration (yeasts) is reached. =============================================================

This discussion continues in the next post-- DCW

-- Dan Wing Wag...@connriver.net

slki...@aol.com

5/27/98

Dan,

Thanks for the great info! I'm still digesting much of it (if you can forgive the pun), but I had a few thoughts. I found Michael Ganzle's "comment #1" especially informative.

wag...@connriver.net (Daniel Wing) wrote:

> > Taken together, one can state the following

> [condensed by Sam]:

> > For sourdough lactobacilli

> o 32 - 33C = optimum growth

> o 37C and 20C = double generation time

> o 39C and 15C = fourfold generation time

> o 41C and 4C = no growth observed

> For sourdough yeast

> o 28C = optimum growth

> o 32C and 20C = double generation time

> o 34C and 14C = fourfold generation time

> o 35C and 8C = no growth observed

This, I think, is very useful and enlightening information that has direct bearing on some of the recent r.f.s. discussions, as well as some of the FAQ entries. So I thought I'd talk about some of them...

First there is Dick's time/temperature formula, which is based on the assumption that "it is usual for biological reactions to double in velocity for each 10C rise in temperature, between freezing and heat death." This formula works well for rising times, and 10C is a decent approximation of the combined data we see above. What the assumption doesn't explain is the steep drop in population growth at (sub-cell-death) temperatures above "optimum," and that "zero growth" is observed above freezing. That said, it should work very well between ~10C and ~32C.

So we see that most of the interesting growth phenomena (particularly with respect to yeast versus bacterial growth) happen at extreme temperatures. This has direct bearing on certain suggested methods of starter maintenance:

High Temperature Maintenance

The FAQ contains an interesting entry on how one might manipulate the microbiological population of a starter by refreshing it at high temperature. This is summarized in http://www.nyx.net/~dgreenw/whattemperatureshouldmysta.html One should carefully note (and I would suggest that the FAQ be annotated to reflect) that "if several refreshments are done above 32C, the yeast will drop out eventually." This would be especially true at, say, 35C/95F when the lactobacilli are still multiplying at a high rate while the yeast are at "zero growth."

Low Temperature Maintenance

A lot of us keep our starters in the refrigerator. Many of us keep them exclusively in the refrigerator. The latter practice may not be such a good idea. The data above seems to indicate that yeast may drop out over time if a starter is refreshed at temperatures between 4C/39F (bacteria "no growth") and 8C/46F (yeast "no growth"). I imagine that a 10C/50F temperature would be firmly within the margins of safety, but that seems awfully warm for a refrigerator. Unfortunately, an observation of "froth" or other visible starter activity cannot necessarily confirm the presence of yeast. It is possible to ferment/rise a dough exclusively with lactobacilli.

On the bright side, I imagine it is possible that the yeast in a constantly-refrigerated culture may mutate to become more low-temperature-tolerant, or (more likely) a low- temperature-tolerant yeast may "invade" the culture and take the place of the original yeast. Either way, although you may find yourself with a perfectly good culture, it will not be the same culture with which you began.

This shouldn't affect people who store their starter in the refrigerator but generally refresh it at room temperature.

> In doughs that are continuously operated with a high inoculum (more than about 30%), you'll find more yeast and

> fewer lactobacilli. Eventually, the lactobacilli flora may change, with more acid tolerant lactobacilli (e.g. L. pontis) prevailing.

Many of us feed our starters by "doubling." This seems a very good reason to switch to "tripling!"

> In white wheat flour, the enzyme activities are so low that the organisms may run out of food before the critical pH (lactobacilli) or the critical acetic acid concentration (yeast) is reached.

I wonder if this is true for our typical US white wheat flour, which includes ~.1% barley malt for the enzymatic content. I never supposed that this might be so... I'll have to reconsider my thoughts on the use of diastatic malt syrup as a worthwhile sourdough dough additive.

Sam Kinsey slki...@aol.com

Larry Caldwell

/29/98

In article <6khpco$4l7$1...@nnrp1.ddejanews.com>, slki...@aol.com wrote:

> The FAQ contains an interesting entry on how one might manipulate the microbiological population of a starter by refreshing it at high temperature. This is summarized in [ ... ]

> A lot of us keep our starters in the refrigerator. Many of us keep them exclusively in the refrigerator. The [ ... ]

> take the place of the original yeast. Either way, although you may find yourself with a perfectly good culture, it will not be the same culture with which you began.

If you really are attached to a particular starter, it's simple enough to freeze a sample. Constant characteristics may be important to a commercial baker, but I don't see any reason for the sourdough hobbyist to be so limited.

I play with my starter. I particularly like to change what I feed it for a month or so and see what it does. I started it with half a dozen lactobacillus sources, and I bet all of them are still in there, in varying concentrations that feeding can change.

I commonly feed potato starch. I also have tried rye flour, oat flour, barley flour and corn flour. I was using milk for a while, but it started to get to "limburgery" to the point that the cheese flavor was coming through in the finished bread, so I dropped the milk and the flavor shifted back. The corn flour made a real pucker power sour mash. I didn't feed 100% corn, but mixed it half and half with wheat flour.

I never refrigerate the starter. I keep it on top of the refrigerator, where the temp is 23 degrees C. When I feed it, I use hot water, though not so hot as to kill the culture. If I'm only feeding a little, I use almost boiling water, if I'm doubling or tripling I use hot tap water. Except sometimes I don't feel like it and use regular tap water.

I haven't had a bit of trouble attaining a fine tasting sourdough. Some types of starter do better in some recipes than others. The milk based starter made the best double sponge Swedish Rye, but was too strong flavored for sourdough french.

It's all in how you cook. An amateur can afford to take more risks than a professional.

-- Larry

slki...@aol.com

5/29/98

Larry,

I agree that one should be open to experimentation. Also, if what you're doing makes bread that you like, more power to you. That said, there are some comments I'd like to make on your post for the sake of clarity.

In article <tDbb10O5...@teleport.com>,lar...@teleport.com (Larry Caldwell) wrote:

> > If you really are attached to a particular starter it's simple enough to freeze a sample.

Actually, it's not so simple. There is fairly strong evidence that many sourdough organisms will not survive freezing. On the other hand, Carl has been drying and freezing his sourdough culture for years (see http://www.nyx.net/~dgreenw/canifreezeordrymystarter.html). However, it is likely that Carl's starter has responded to this treatment by evolving freeze-tolerance. Such tolerance cannot be assumed for all sourdough cultures. Anyone who plans to freeze a sourdough culture (other than Carl's) would be well-advised to "test-freeze" a sample and make sure that it recovers from freezing with its unique characteristics intact.

> Constant characteristics may be important to a commercial baker, but I don't see any reason for the sourdough hobbyist to be so limited.

Well, there are limits and there are limits. I would never suggest that home bakers abandon experimentation. However, unpredictable starter behavior is often cited as one of the most limiting aspects of sourdough baking. Mistrust (or misunderstanding) of one's starter is a primary reason why some bakers chose to rely on added bakers' yeast to leaven the dough.

> I play with my starter. I particularly like to change what I feed it for a month or so and see what it does. I started it with half a dozen lactobacillus sources, and I bet all of them are still in there, in varying concentrations that feeding can change.

I'll take that bet, because I bet that you're wrong there. As I showed in my previous post, temperature (especially >35C) can have a profound effect on the microorganisms in your starter. Dan's recent "technical" posts also showed how the percent inoculation (and consequent pH effect) can cause certain lactobacilli to drop out while others become dominant. Etc. Etc. Etc.

A starter is basically a little "Darwin Machine." As the environment changes, the microorganisms living in it will either change and adapt or they will be replaced by better-adapted microorganisms. The pre- existing microorganisms do have a survival advantage, because they have established a mutually beneficial symbiosis. But a big change in environment could easily take away that advantage. It is true that certain sourdough cultures have been scientifically shown to retain the same microorganisms over many, many years -- but these are consistently-maintained cultures.

> I was using milk for a while, but it started to get too "limburgery"

I imagine that the milk fat was turning rancid.

> I never refrigerate the starter. I keep it on top of the refrigerator, where the temp is 23 degrees C. When I feed it, I use hot water, though not so hot as to kill the culture. If I'm only feeding a little, I use almost boiling water, if I'm doubling or tripling I use hot tap water.

Like I said, if it works for you -- great. I would never recommend this kind of starter maintenance to anyone. At the temperature you are keeping your starter, one would have to triple it at least once a day to keep the pH low enough for L. sanfransisco (assuming that you want that kind of lactobacillus) and to keep whatever microorganisms you have in there healthy. To come along and add "almost boiling water" to this starter will surely kill off plenty of the remaining yeast/bacteria. From what you describe, I would imagine that the microbial population of your starter is in almost constant change.

Sam Kinsey slki...@aol.com

Larry Caldwell

5/31/98

In article <6kmqjs$fic$1...@nnrp1.dejanews.com>, slki...@aol.com wrote:

> > I was using milk for a while, but it started to get too "limburgery"

> I imagine that the milk fat was turning rancid.

I guess I forgot to mention that I used nonfat milk. I think it was actually penicillin, and I was getting a true "limburger" culture going in there with the sourdough. It was certainly interesting, and actually quite tangy, but it did have an unfortunate aroma that didn't cook completely out. Dropping the dairy products solved the problem.

It may have been a yeast strain. Anyone who has ever worked with salt rising bread knows that yeast can make some pretty pungent odors. Some day I'm going to develop a saline starter and see what it tastes like. Summer is coming, and I could set up a rising box in the garage when it gets warm enough. Making salt rising bread in the kitchen is rude. :)

-- Larry

Daniel Wing

5/25/98

Rye is second to wheat as a bread grain **

Comment No 2: If discussing rye, it may be of importance, that rye quality depends heavily on the weather conditions during the harvest: if is is very humid before and during the harvest, sprouting starts, leading to increased amylase activity. In a dry year, the amylase activities may be rather low, so that the problem with the acidification is not very prominent. It may also be noted that rye not only has a higher amylase activity, a but also a higher protease activity, which is important for the flavor development.

---------------------------------------------------------

In all, about 72 percent of the original kernel is left in most of the white flour produced in the United States. **

In Germany, the most common bread flour is wheat type 1050 (1.050 g ash per kg) or rye type 1180. Many breads are “Vollkornbrotł. Type 550 (or 55) is used only for white wheat bread, not a very big share in the market.

-----------------------------------------------------

Rye flour is commercially ground to a range of colors and particle sizes, and the nomenclature is confusing. **

If very coarsely ground flour is used, it should be swollen in water before the dough mixing, Otherwise, it will take up water during dough fermentation and proofing, and result in too stiff doughs. This is called “Quellstueckł by German bakers. As far as the enzyme activities go, see comment No 2 above. The difference in enzyme activities is also important for the microorganisms: in rye flour they always have enough sugar available due to the high enzyme activities, whereas in white wheat flours, glucose (but not maltose) may be depleted during the fermentation.

----------------------------------------------------------------

Rye flour contains a great deal of amylase. Rye amylase resists inactivation by heat to a greater extent than wheat amylase. It is so resistant to inactivation that it is still active when the gelatinization temperature of rye starch is reached in the oven **

This is a very nice explanation. Also: see above (Comment No 2)

----------------------------------------------------------

No laboratory test assesses taste, even though there are real differences in the taste and texture of bread baked from otherwise similar flours. **

This would be impossible, since the flour has no flavor whatsoever. I’ve been preparing a research proposal recently with Markus Brandt and Prof. Hammes in our lab, and Prof. Schieberle, probably the best expert in flavor chemistry of bread, so I’ll go into some detail (and refer to it as comment No 3 later on). It may be useful to distinguish between taste and aroma. Taste happens on the tongue, where only salty, bitter, sweet and sour can be evaluated. Aroma is perceived in the nose: during chewing, the volatile compounds diffuse to the receptors (mind that acetic acid, but not lactic acid is volatile. Thus, the latter is just sour, while acetic acid has aroma). There are about 15 compounds each (about 10 of them are the same for wheat and rye bread, furthermore, crust and crumb have different aroma volatiles) with which the impression of rye or wheat bread is given (This is work of Prof. Schieberle in Munich).

To group the compounds according to their generation in dough, one may say that:

i), they are produced by fatty acid oxidation by cereal enzymes upon dough mixing (several baking aids contain soy flour with additional lipoxygenase activity, and prolonged storage of whole flour leads to rancidity as well). These compounds have a “green, “bitter “tallowy or “metallic taste - not very pleasant. Lactic acid bacteria and yeasts do inactivate these compounds in part, thus, fermentation reduced the “rancidity of the bread.

ii) aroma compounds are produced by yeasts and lactobacilli. More of them by yeasts, probably, though acetic acid also plays an important role. These compounds often give a “flowery, “yeasty or “malty flavor.

iii) The Maillard reaction is extremely important, especially for the crust aroma compounds. However, the precursor chemicals for this type of reactions are amino acids, and the levels of amino acids in flour is very low. In wheat, there is little, if any proteolytic activity (proteases degrade protein to amino acids), so, whatever amino acids there are produced by enzymes of lactic acid bacteria (there has been nice work done on proteolysis in wheat dough by Dr. Marco Gobbetti at the University of Perugia). In rye, the proteolytic activity of the flour is much higher, but the proteases need acidification to a pH below 5 to have their optimum activity (and, of course, a long fermentation time gives the enzymes more time to work). Sourdough yeasts are consuming amino acids, meaning a sourdough with a high yeast count has fewer amino acids than a dough containing only lactobacilli. Addition of excess amounts of baker’s yeast (>4%) also leads to an increase of Maillard compounds, but that may not be the aroma a sourdough baker is looking for. The most important flavor compound in rye crust, methional, as well as in wheat crust, 2-acetyl-pyrroline, are Maillard products of the amino acids methionine and ornithine, respectively.

As I mentioned, we’ve been preparing a research proposal to figure out which of the aroma compounds or aroma precursors (meaning chemicals converted to aroma compounds during baking) are formed by which microorganisms. In other words, other than acetic acid production, we don’t know whether or not aroma is produced by yeasts and lactobacilli of sourdough. There are a few good working hypotheses: Some, but not all strains of L. sanfranciscensis convert arginine to ornithine (MOST important flavor precursors in wheat), so this metabolic activity may be of importance. Several other compounds are produced by yeasts (but we don’t know whether the sourdough yeasts are more active than baker’s yeast), and all L. sanfranciscensis does convert the fatty acid oxidation products to chemicals with less or no aroma intensity - but how this activity compares to straight, baker’s yeast dough, we don’t know.

============================================

continued in next post-- DCW

-- Dan Wing Wag...@connriver.net

Daniel Wing

5/25/98

Amylase digestion of this damaged starch provides sugar for fermentation and produces dextrins, a class of polysaccharide that is quite hygroscopic.**

See comment No 2: lactobacilli and yeast rely on the amylase of the grain as they don’t have starch degrading enzymes. A Spanish group has looked for the development of maltodextrins during sourdough fermentation: as lactobacilli and yeasts don’t like the oligosaccharides, they accumulate during fermentation. The Spanish (C. Collar and M. Martinez-Anaya in Valencia, Spain) think that maltodextrins may delay bread staling, though.

----------------------------------------------------

because that enzyme (PHYTASE) is most active in dough between pH 4.3 and 4.6, prolonged fermentation with mixed cultures (an acid medium) will **

It is true that the enzyme is most active IN DOUGH between pH 4.3 and 5, however, the reason is not optimum enzyme activity at this pH, but the fact that CaMg-Phytate is insoluble and thus not available for enzymatic cleavage at a higher pH. (The first work during my diploma thesis was to look for phytase enzymes in lactobacilli from sourdough. After 8 weeks, I figured out that there is none, and shortly thereafter it became clear that both wheat and rye have sufficient phytase activity, all it takes is some acidification).

-----------------------------------------------------

I chose to write "natural leaven" because it is less awkward than "mixed ferment cultured from the environment and sustained with repeated inoculation." ** “

Sustained with repeated inoculation is better than anything I was writing to say the same thing. Cultured from the environment is certainly true - L. sanfranciscensis and the yeasts must come from somewhere - but somewhat misleading, as these organisms most probably do not originate from the grain, or the flour (Marco Gobbetti, whom I mentioned earlier has been looking for L. sanfranciscensis on all kinds of Italian wheat flours, and he has not found any. In every Italian dough “sustained with repeated inoculation you’ll find L. sanfranciscensis to be the dominating species, though. No other scientist has been able to isolate L. sanfranciscensis from any other source than sourdough, but all sourdough “sustained etc Contain this organism as the dominating flora. A possible source may be the humans: there are all kinds of lactobacilli thriving in the mouth, the intestines, etc. Hammes met a South African Microbiologist who claimed to have isolated L. sanfranciscensis from the teeth of pre-school children. The data is not published, so I don’t know what science is behind this claim. But, wherever L. sanfranciscensis comes from, it most probably does not come from the flour. (That’s comment No 4)

--------------------------------------------------------

Natural leavens are not all the same. Not only are there many strains of yeast and bacteria that can form them, we need terms in English for the various stages of natural leavens. **

One may think of all the “sourdough stages as just a piece in an infinite chain of repeated inoculations. Some sourdoughs are quite close to infinity, as far as the generations go. You certainly know Carl Griffith sourdough (claimed to have survived since the days of the Oregon Trail); the dough we’ve been working with, Böcker Reinzucht Sauer, a rye starter that has the reputation of being one of the best rye starters available (Spicher says so, we do, and the Spanish group has been working with it as well), is well above 50 yeast “old. Then, the definition of e.g. “three stage sourdough processes does make no sense. What makes is fascinating is that the microbiology of Böcker Reinzuch Sauer HAS NOT CHANGED in the past 30 yeast, i.e. since people started to do microbiology with the dough. There are two strains of L. sanfranciscensis, and one yeast, C. milleri. The “modeling I mentioned in comment No 1 was done with these three organisms. Remarkably, the two strains of L. sanfranciscensis reacted almost identically on changes of pH, temperature, etc. Then, the definition of e.g. “three stage sourdough processes does make no sense. -----------------------------------------------------

This selection leaves it (COMMERCIAL YEAST) specialized for a narrow range of fermentation characteristics that favor rapid gas production over flavor production or other possibly desirable qualities (resistance to bread spoilage, for instance). **

This could be also said for sourdough lactobacilli and yeasts: As the dough is continuously refreshed, those strains are selected that grow fastest in dough. This is probably a much more harsh and effective selection than what is done for the baker’s yeast. Fortunately, what is good for the sourdough lactobacilli seems also to be good for bread quality (There are other microorganism in fermented food that require the man-made habitat: e.g. Tetratenococcus halophilus growing only in soy mashes, and Oenococcus oeni, occuring in wine only.) What is important, is that as soon as you change your parameters, you may change the microflora. E.g., if the dough is fermented at 33 instead of 28°C, yeasts will drop out, and above 37 - 38°C, the flora will change altogether, with thermophilic lactobacilli dominating. See comment No 1.

---------------------------------------------------------

The yeast and bacteria in natural leavens are considered native or wild because the cultures are started with organisms recovered from environmental surfaces. **

The fermentation starts with flour microorganisms, but - see comment No 4 - the sourdough lactobacilli and yeasts do probably not originate from the grain. And later: the organisms have been refined by thousands and thousands of sourdough - refreshments, much more effective than any microbiologist of food scientist could ever be. (Besides, we know what kind of organisms do grow in sourdough - but how flavor production takes place, and which fermentation products delay bread staling is largely unknown - so other than gas production, I could not think of a property of lactobacilli in which to select a strain. And gas production, as you’ve rightfully pointed out, is certainly not the right criterium.) ----------------------------------------------------------

The conditions under which a culture is developed and then maintained can select out strains of yeast and bacteria that have special characteristics, and the typical yeasts present in the air and soil in different locations also vary somewhat in their properties and their interactions with lactobacilli. This kind of co-evolution makes some natural leavens remarkably stable when regularly maintained. The more regular and consistent the maintenance, the more predictable the rising power, microbiological composition, acid balance (acetic/lactic) and acid production will be. **

This is important (although I don’t think that the yeasts from air and soil do matter). But the consistency in maintenance is crucial (one is allowed to err to one side or the other from time to time, though).

------------------------------------------------------------------- ============================================

continued in next post-- DCW

-- Dan Wing Wag...@connriver.net

Daniel Wing

5/25/98

Since many people new to natural leavens would like to bake San Francisco sourdough, Desem bread, or German rye bread, let's look at some of their characteristics, as determined by their leavens, ingredients, and processes. **

The microflora of German rye sour and San Francisco sourdough is (almost) identical. The difference is raw material and production process. Prof. Hammes thinks that L. sanfranciscensis isolated from wheat or rye may have different properties (e.g. degradation of arginine to ornithine, see comment No 3, or proteolytic activity (see comment No 2: wheat has less proteolytic activity by itself than rye). He still has to prove his point, though. -----------------------------------------------------------

That yeast is also resistant to a natural antibiotic made by the bacteria. **

The most “antibiotic compound in sourdough is acetic acid. Although I mentioned earlier that Candida milleri from Böcker Reinzucht Sauer (The Saccharomyces exiguus described by Kline and Sugihara has been renamed to Candida milleri as well) is more sensitive to acetic acid than the lactobacilli, it certainly is much more resistant than baker’s yeast. Gobbetti says that L. sanfrancisco produces other organic acids that may inhibit yeast growth, but I don’t know whether or not the concentration in the dough is high enough to make a difference. As far as I know, no other antimicrobial compound in dough has been characterised. -----------------------------------------------------------

Most German rye bread has at least 30 percent rye **

I have the figures: 60% is “mixed rye bread containing both rye and wheat, but more of the former. As far as the bread goes, rye only about as important as wheat only. The situation is different for bagels, pretzels, and so on. There is increasing interest in wheat sourdoughs: the 1 - 5% addition of sourdough, which is sometimes replaced by a dried and “dead sourdough works, but not quite as well as it could. Which is why industry is funding flavor research at the Universities of Hohenheim and Munich...

----------------------------------------------------------

Vollmar and Meuser showed that the rate of bacterial reproduction after inoculation is self-regulated, within limits: if you add a small inoculum, the bacteria will multiply faster than they will if it is larger, so the static population (say 1,650 million cells/cc) is reached at the same time in either case, about three and one-half hours. **

The Vollmar and Meuser sourdough machine is not a very good example: as pointed out in comment No 1, it operates with an inoculum of 50%, which makes the dough so acid from the beginning on the lactobacilli don’t like to grow fast. Between 1 and 20% inoculum, lactobacilli grow at the same speed (giving rise to the dependency of fermentation time and inoculum size explained earlier). The Vollmar and Meuser machine also has a rather high yeast content (if you’ve read their publication in Cereal Chemistry; yeasts are above 100 million or more than 10% or the total cell counts, while “normal starters such as the San Francisco starter of the Böcker Reinzucht Stater have only around 10 million or about 1% of the total cell count. --------------------------------------------------------

When cultures are fermented at higher temperatures, non-pathogenic acid-tolerant contaminants such as Pediococcus (makes too much lactic acid) and Acetobacter (makes to much acetic acid) can intrude and dominate, affecting taste. **

Pediococcus is probably less acid tolerant than L. sanfranciscensis, but it grows at higher temperatures (as mentioned above, sanfranciscensis does not like more than 35 - 37°C. Acetobacter is of no importance in sourdoughs: it strictly requires oxygen for growth, and sourdough becomes anaerobic (=without oxygen) very quickly due to the metabolism of yeasts and lactobacilli. If you’ve ever seen a vinegar fermenter you will notice that several hundred liter of air are pumped through a liter of vinegar during an hour: it is almost impossible to aerate sourdough in such a way.

--------------------------------------------------------------

Dr. Sugihara, who participated in the characterization of the flora of San Francisco sourdough and several other cultures, was asked whether natural sourdough cultures could be contaminated with commercial yeast. His reply was no, not if you have a stable culture that is continuously maintained with the same conditions and ingredients. **

Dr. Sugihara is certainly right here. There was an experiment done by a Dutch group: baker’s yeast didn’t survive more than two refreshments. I think that it’s the acetate that kills the yeast as its less acetate tolerant than sourdough yeasts. And to the margin note right next (CONCERNING THE ABILITY OF BACTERIAL FERMENTATION TO RAISE A LOAF OF BREAD, WITHOUT YEAST): We’ve done the experiments, it works quite well without yeast. The volume is somewhat smaller, though. Markus Brandt has estimated the contribution of yeasts and lactobacilli to gas production in a “normal sourdough: about 50% comes from lactobacilli and yeasts each. The yeasts are fewer in numbers, but larger in size. --------------------------------------------------------

Bakers are interested in the acids produced by leaven microbes because much of the distinctive flavor produced by leaven microbes comes in the form of organic acids that are products of fermentation. **

The production of lactic acid in dough in determined mainly by the buffering capacity of the flour, i.e. the ash content. Dough yield and temperature are much less important; as far as Spichers investigations go, I think that the higher lactic acid content of doughs with higher temperatures or higher dough yields he measured is due mainly to the faster fermentation at these conditions. (this holds true if you calculate the lactate produced on the amount of flour in the dough: this ratio is fairly constant). The amount of acetic acid produced is controlled mainly on the availability of fructose. L. sanfranciscensis produced lactic acid and ethano (and carbon dioxide) from maltose or glucose. If the organism wants to produce the more oxidized end product, acetic acid, another substrate must be reduced. L. sanfranciscensis reduced 2 moles of fructose to mannitol per mole of acetic acid formed. The ratio of mannitol to acetic acid in dough is about 1.8, fairly close to the theoretical value of 2 if fructose was the only co-substrate that is reduced. During fermentation, L. sanfrancisco starts to produce lactic acid and acetic acid first, and forms lactic acid and ethanol only if the fructose is depleted. There is a lot of fructose in dough, but not all of it is available for the lactobacilli. Yeasts liberate some of the fructose bound in glucofructans that thus becomes available for the lactobacilli (there is some nice work that has been done by the Sugihara group, Saunders et al., cereal chemistry, 1972 or 1973). If you to too high with the temperature, you slow down yeast growth, and the acetic acid levels in the dough decrease. For bakers, an easy way to increase the acetic acid content is to add sugar that is sucrose, a consisting of glucose and fructose). This won’t increase the total titrable acidity, though, as that is determined by the buffering capacity. Sugar addition (not too much, 1 or 2%) may speed up fermentation in white wheat flours: as mentioned above, in contrast to whole wheat flour and rye flours, the enzyme activities and thus the sugar concentrations are rather low and may limit microbial metabolism. As far as the influence of acetic acid and lactic acid on flavor go: lactic acid has no influence on aroma, only on taste, while acetic acid is an aroma volatile. So, I think it is not so much the ratio of lactic to acetic acid, but more simply the acetic acid content that matters. ------------------------------------------------------------

Natural leavens should be actively fermenting and reproducing when they are incorporated into a dough **

Yeasts in dough don’t have to rely on oxygen for growth: if that were the case, they would not be there.

----------------------------------------------------------------------

The more accepted and consistently successful way to store a culture for a month or so is to make a fresh and very stiff storage leaven, put it in a well covered vessel ... **

Such leavens may keep up to almost three month (my sister had a baby in March and didn’t use her starter for almost three month. It was stored the way you described here, and did come out well upon refreshment. The Böcker Reinzuchtsauer is also distributed as stiff, refrigerated product. I think the company does not guarantee storage stability of more than 4 weeks, though.)

----------------------------------------------------------------------

Still there may be someone out there who does need to start a leaven because of some terrible misfortune-- **

I think it does not matter when the first batch of a new sourdough stinks - the good bacilli will come out eventually, and they may come faster if fermentation is done around 25 - 30°C (as mentioned earlier, the temperature optimum of L. sanfranciscensis is 32 - 33°C). There has been nice work done in Rudi Vogels lab on the microflora of a freshly started sourdough: first, there are Enterobacteria (Escherichia coli, Salmonella, Enterobacter), highly undesirable organism that stink terribly, then there are homofermentative lactobacilli (good, but no gas production), then acid-tolerant, heterofermentative lactobacilli. I think, this took about 48 hours at 30°C. The stink at the beginning does not matter as the organisms will be diluted out or die eventually. No L. sanfranciscensis, though, these will occur only after repeated refreshments. Peter Stolz of the Böcker company told me that it takes about two weeks of repeated inoculations to get a good “sanfranciscensisł sourdough. I don’t know whether or not this process was sped up in his case as, due to his workplace, his skin is all covered with L. sanfranciscensis.

-----------------------------------------------------------------

My biggest disagreement with her, though (NANCY SILVERTON), is about the amount of material one should use in a starter. **

I agree with you: one g of dough is one billion lactobacilli and 10 million yeasts: more than enough. In the lab, I’m doing most experiments on a 1/10 ml scale, for dough refreshments at home, it does not get much smaller than 10 g: it’s difficult to handle smaller amounts.

-------------------------------------------------------------

If leaven refreshment intervals are excessive **

The main criterion of sourdoughs containing L. sanfranciscensis is the repeated, frequent refreshment (not counted the storage in the refrigerator). Peter Stolz said that one every 24 hours will suffice, if intervals are much longer than that (lets say more than 3 days), different, more acid tolerant organisms may evolve (e.g. L. pontis as found in the Vollmar and Meuser Breasd machines: these are refreshed frequently, but with a very high inoculum). ---------------------------------------------------------------------

Refreshment schedules are always dependent on temperature. **

See my earlier comment on the temperature dependency of growth of L. sanfranciscensis and Candida milleri. Most of the typical sourdough yeasts resemble C. milleri with respect to the temperature sensitivity (i.e. no growth at 37°C). -------------------------------------------------------------

Acidity can be expressed as flavor (an acid flavor), as pH, or as total acidity. **

That a good explanation of the total titrable acidity concept. (I find students almost done with their degree still have difficulties with this concept). -------------------------------------------------------------------

At any given temperature the thinner starter will ferment faster and reach a lower pH; but will not contain as much acid. **

If you calculate the amount of acid produced on the weight of the flour rather than the dough weight, the outcome -lactic acid per g flour - should be pretty independent on dough consistency (not if very stiff doughs are produced: the combined salt and acid stress leads to a decreased acid production). Markus Brandt observed this in doughs (rye flour, TA 180) if more than 2% salt were added.

-------------------------------------------------------------------

Together, caramels and Maillard products are responsible for much of the flavor and aroma of fresh yeasted bread, although of these two, Maillard products are much more intensely aromatic. **

This is right for both yeasted breads and sourdough breads, however, it is important to note that whatever chemicals are reacting with each other during baking must be formed during dough fermentation. (Schieberle in Munich has done several nice studies: he supplied doughs with amino acids and demonstrated that the levels of aroma compounds in the bread were increased). So, formation of aroma precursors during dough fermentation is crucial for the Maillard reaction.

==================

The end of this set of posts-- DCW

-- Dan Wing Wag...@connriver.net

Dick Adams

5/29/98

Dan's Gänzle Report

About 4 installments posted 4/25/98 entitled "Long Technical Post" (1-4) by Dan Wing <wag...@connriver.net>:

Having been duly inspired and mystified by the subject report, I should like to ask Dan Wing if he will suggest some ways in which Professor Gänzle's wisdom can be applied in practice to recreational sourdough bread making.

>...Since many people new to natural leavens would like to bake

>San Francisco sourdough, Desem bread, or German rye bread, let's look at some of their characteristics, as determined by their leavens, ingredients, and processes...

It would be valuable to have that information summarized as to pertaining to SF type white sourdough bread, on the one hand, to German rye bread on the other. (Desem does not seem to be a big subject at r.f.s.)

I have been particularly amazed by the news that one of Professor Gänzle's colleagues is apparently counting microorganisms in dough. To me, that seems like making a census of monkeys and snakes in the bush (from an aircraft).

--- Dick Adams

defau...@domain.com

6/2/98

Dan's Gänzle Report

Dick Adams wrote

> About 4 installments posted 4/25/98 entitled "Long Technical Post" (1-4) by Dan Wing <wag...@connriver.net>:

> > Having been duly inspired and mystified by the subject report, I should like to ask Dan Wing if he will suggest some ways in which Professor Gänzle's wisdom can be applied in practice to recreational sourdough bread making.

The mystic may arise from the fact that the "long technical post" was written as part of a personal communication and not for a large "audience": things may have gotten a little bit out of context. As far as the application to recreational sourdough bread baking goes, it should contain information as to how acid production in sourdough is controlled, and how the sourdough starter can be treated to keep the lactobacilli happy. As the organisms are pretty much the same in white wheat sourdough and rye sourdough, this information relates to either one. (To my thinking, the differences in taste between "San Francisco Sourdough Bread" and other breads are more likely to result from the different raw material, fermentation and kneading process and baking than from the differences in the sourdough starter). As far as other subjects go - influence of sourdough fermentation and raw material on aroma and texture - I don't have much more to offer than the fact that sourdough bread usually tastes better than "straight yeast" bread (which most of you probably know), and a few working hypotheses.

(By the way, you're a little bit ahead of time as far as my academic merits go.)

> > > I have been particularly amazed by the news that one of Professor Gänzle's colleagues is apparently counting microorganisms in dough. To me, that seems like making a census of monkeys and snakes in the bush (from an aircraft).

> > --- > Dick Adams

The counting is a simple method used in every microbiology lab: One gram of sourdough contains about 2 billion of lactobacilli (microbiologically spoken, a few hundred million more or less don't matter). To count, the sourdough is diluted 1 in 10 million ( 7 one in ten dilutions) and poured in an agar plate. Each of the about 100 cells of the dilution starts to grow and is visible as a colony a few days later. Or, to translate to the census of monkeys in the bush: Distribute the monkeys evenly i n the bush (making sure that they can't mix afterward) and wait until the "families" produced by each (pair of) monkeys is big enough to be visible from the aircraft...

Michael Gänzle

gan...@uni-hohenheim.de

Dick Adams

6/3/98

Dan's Gänzle Report

Michael Gänzle <> wrote in message <35743CD9...@domain.com>...

>(By the way, you're a little bit ahead of time as far as my academic merits go.)

Sorry, couldn't wait. We need a Professor right now!

>The counting is a simple method used in every microbiology lab...

So it seems like we can count on Markus' counts.

What I hope for most is a temperature time plot (or other such instruction) to determine how times should be adjusted for varying temperatures to get optimum ( culture feeding interval | sponge development time | rise time ). The data presented seem to give a few points on such curves, quite similar (in shape and slope on semi log plots) for yeast and bacteria.

It was interesting to observe that yeast growth relative to bacterial growth is retarded towards the high and low temperature limits. So when Andreas tells us the bacteria "like" high temperatures, he is meaning that they tolerate high temperatures better than yeast does. No doubt some others will also perceive that this high, and similar low, temperature behavior may provide a means to get really sour culture and sponge. (But I can't imagine why one would need those, since a yeasty culture/sponge works best, at least for white SD bread.) It also makes it seem silly that some people advise to "retard" at ~50 F. for sourness/flavor development, since the effect desired seems to occur at the practical limits of the temperature time function, not in the middle of it.

Several things continue to baffle me (well, more than that, but let's take a few):

If the bacterial generation time is shorter than yeast's generation time, why doesn't periodically fed starter culture become all bacteria?

Another baffling thing is the accumulation of acids and other metabolic products as they may affect growth kinetics. Not only that, but also the suspicion that bacteria may thrive on yeast deciduem, which would lead one to suspect that bacterial growth may accelerate when yeast becomes disadvantaged by its depletion of its nutrients. These things make it hard to believe that the compound system may be described by very simple rules.

My practice of maintaining my starter culture (with bi- or tri weekly feedings ) in the refrigerator appears to defy logic (since yeast, by Markus' numbers, does not seem to grow at refrigerator temperatures, though bacterial growth may only be impeded). But I guess one could assume that my organisms have ( adapted | mutated | changed | whatever ). SDI's reported practice of maintaining their cultures in the refrigerator with semiannual feedings seems perhaps a bit off base. Carl G. seems to have the right idea, as well as the majority of home SD bakers who incubate their cultures at warm temperatures after feeding and before returning the culture to the refrigerator for short, like weekly, intervals.

A third baffling thing is the relationship between number of cells and activity. It would be nice to be able to assume that the concentration of microorganisms predicts their activity (leavening, flavoring, etc.). If one were to attempt to predict practical parameters from cell count data, some assumptions about that relationship would seem to be necessary.

Be assured, my esteemed Professor, that there is a world of difference, in my case, between serious confusion and desire to pick nits.

(Here in USA, all vat is needed to be a Professor is to talk a little bit funny). (Umlauts are good, too.)

--- Dick Adams

P.S. I have still not found the keystrokes for the little superscript 0 that designates degrees.

so...@spamlesssoleassociates.com

6/3/98

Dan's Gänzle Report

"Dick Adams" <dick....@bigfoot.com> wrote: » »P.S. I have still not found the keystrokes for the little

»superscript 0 that designates degrees.

Try ALT-0186 for Dº

-- -Kenneth

If you email please remove the "SPAMLESS."

nos...@auerbach_at_unity.ncsu.edu

6/3/98

Dan's Gänzle Report

In <6l3sm2$j...@bgtnsc02.wworldnet.att.net>, on 06/03/98 at 12:11 PM, "Dick Adams" <dick....@bigfoot.com> said:

<- It also makes it seem silly that some people advise to "retard" at ~50 F. for sourness/flavor development, since the effect desired seems to occur at the practical limits of the temperature time function, not in the middle of it.

I would love to know how the technical underpinnings of retarding. The data are that retarding improves flavor. The question is how? As Dick now admits, the interaction effects are complication so the old 10 degree/doubling rule tells a miniscule part of the story.

-- Regards, David

"What would life be without arithmetic, but a scene of horrors?" -Rev. Sydney Smith, letter to young lady, 22 July 1835

Check out http://www.nyx.net/~dgreenw/sourdoughfaqs.html for sourdough FAQs

----------------------------------------------------------- David Auerbach nospam@auerbachatunitydotncsudotedu fix the above for the real address -----------------------------------------------------------

Dick Adams

6/3/98

Dan's Gänzle Report

nos...@auerbach_at_unity.ncsu.edu wrote in message <35759339$3$nhreonpu$mr2...@news.duke.edu

>As Dick now admits, the interaction effects are complication so the old 10 degree/doubling rule tells a miniscule part of the story.

I admit nothing! I will use the old rule until something better comes along. Anyway, it is not a rule, but a means of estimating. The Brandt numbers crudely fit a 5 or 6 degree (ºC.) rule through a usable range. I am betting on a 8º "rule". These kinds of rules are for lumping everything, even that which surpasses human understanding.

--- DickA

nos...@auerbach_at_unity.ncsu.edu

6/3/98

Dan's Gänzle Report

In <6l45fu$p...@bgtnsc02.worldnet.att.net>, on 06/03/98 at 02:38 PM, "Dick Adams" <dick....@bigfoot.com> said:

<- nos...@auerbach_at_unity.ncsu.edu wrote in message <- <35759339$3$nhreonpu$mr2...@news.duke.edu

<- >As Dick now admits, the interaction effects are complication so the old 10 degree/doubling rule tells a miniscule part of the story.

<- I admit nothing! I will use the old rule until something better comes along. Anyway, it is not a rule, but a means of estimating. The Brandt numbers crudely fit a 5 or 6 degree (ºC.) rule through a usable range. I am betting on a 8º "rule". These kinds of rules are for

As I said. The question is "estimating" what? The What that is estimated is a miniscule part of the story, as we both know.

-- Regards, David

"What would life be without arithmetic, but a scene of horrors?" -Rev. Sydney Smith, letter to young lady, 22 July 1835

Check out http://www.nyx.net/~dgreenw/sourdoughfaqs.html for sourdough FAQs

Darrell Greenwood

2/15/97

Dan Wing was kind enough to forward to me the correspondence below together with permission to post. I did a small amount of copy editing. Hopefully I didn't affect any nuances of meaning but just got rid of a few typos.

My thanks to Michael and Dan for very graciously sharing their correspondence.

Cheers,

Darrell

----------------------------------------------

Date: Thu, 13 Feb 1997 10:49:32 +0100 (MEZ) From: Michael Gaenzle To: wag...@connriver.net Subject: sour dough microbiology MIME-Version: 1.0

Dear Daniel Wing!

Your letter to Prof. Hammes has reached Hohenheim, and Prof. Hammes has asked me to take care of the communication. I am a Ph.D. candidate in Hammes' lab working on the physiology of sour dough lactobacilli.

Please feel welcome to address questions to us concerning sour dough microbiology and technology! I will mail two recent publications or our lab concerning the physiology of sour dough lactic acid bacteria by mail, but as they may take a week or longer to reach you, I will give a few comments on the questions in your letter:

- yeasts do not produce appreciable amounts of either lactic or acetic acids, their main metabolites are ethanol and CO2. If acidification of the dough is desired of required (e.g. if rye flour is used), lactic acid bacteria or organic acids (most commonly lactic or citric acids) are added.

- homefermentative lactic acid bacteria do produce solely lactic acid from maltose or glucose under anaerobic conditions (as they are prevailing in sour dough fermentations). Thus, doughs acidified with homofermentative lactic acid bacteria (LAB) contain but little acetic acid. As homofermentative lactic acid bacteria do not produce CO2, yeast must be added to ensure leavening of the dough.

- In sour doughs with a tradition of continuous propagation (such as the San Francisco French Bread Sour Dough process, German rye sour doughs or sour dough employed in Pannettone production in Italy), heterofermentative lactobacilli, especially L. sanfrancisco, are dominating the fermentation. Heterofermentative lactobacilli produce lactate, ethanol, and CO2 from hexoses (most strains do not ferment pentoses), HOWEVER, if additional substrates are present that serve as electron acceptor to balance, acetate is produced instead of ethanol. I do not know whether or not you are familiar with the concept of the "redox balance": Degradation of hexoses via the pentose-phosphate pathway as employed by heterofermentative LAB results in phosphorylation of ADP to ATP, and in the reduction of NAD to NADH. As there is no use for NADH, it must be oxidized to NAD again. In the absence of other substrates, acetyl-Phosphate is reduced to ethanol, with two NADH becoming oxidized to HAD in the process. If either fructose, oxygen, citrate or malate are present, these become reduced to mannitol, H2O, lactic and acetic acid, and succinate, respectively, and acetyl-P is dephosphorylated to acetate. (This explanation may not be very straightforward, I hope we did a better job in the publications I’m about to send you; these also include a diagram showing the metabolic pathways of L. sanfrancisco). The consequence for the molar ration of lactate:acetate (fermentation quotient, FQ) in sour dough fermentations is, that acetate in produced only if one or more of the above mentioned co-substrated is present. Oxygen is present only in the beginning of the fermentation, and the amounts of oxygen are too low to result in significant amounts of acetic acid, though, in principle, it is possible to increase the acetate content by aeration of dough. Fructose is present in sucrose and other glucofructans with higher molecular weights. Fructose is released from these compounds by cereal or dough enzymes (many strains of L. sanfrancisco don’t even cleave sucrose) and consequently reduced to mannitol by L. sanfrancisco. The ration of mannitol : acetate in sour dough fermentation is approximately 2:1, suggesting that fructose is the most important electron acceptor. Furthermore, citrate and malate are present in the dough in amounts < 10 mmol/kg, these are utilized also.

Thus, the effect of substrates and oxygen on the FQ is nicely explained by the metabolic characteristics of the dominating fermentation organisms. Dough yield (=kg dough per 100 kg flour) and temperature also influence the FQ. Spicher reports that softer doughs lead to an increased FQ; an increase in temperature results in higher amounts of lactic acid, while the amount of acetic acid remains more or less the same, thus, the FQ is increased again. I do not have a straightforward explanation for these phenomena, but changes in dough yield and temperature will result in changes in buffering capacities of the dough, modified activities of cereal and microbial enzymes, as well as a changed ration of yeasts : lactobacilli counts, all of which are likely to influence the FQ.

Yours

Michael Ganzle

------------------------

Dear Michael Gaenzele

Thank you for sending one of the most gracious letters I have ever received in response to any kind of an inquiry. Since I wrote to Prof. Hammes I have been able to copy a number of articles from English language publications by Drs. Brummer, Spicher, Vogel, and so forth. Unfortunately, some of them have been in non-technical journals and were thus short on details, and even the less technical ones were not as clearly and idiomatically written as your letter. I DID have a hard time understanding what was meant by Dough Yield, for instance, although I had figured it out before I got your letter. I am still not sure I understand some of the statements those authors made about the acid content of doughs (such as the units of measurement), but I have been piecing things together by looking at all the articles cumulatively. Your letter has clarified a great deal. I will put stars next to my current questions to make THIS letter easier to answer. Like this *****.

One problem for me was that I did not realize how predominant rye flours were in German sourdough baking. I know that typical rye pentose is about 8% and that pentose viscosity is important in gas-trapping in rye doughs (He and Hoseney, 1991) but I still don't know how an acidified rye dough behaves differently from a more neutral one. ****

Does it affect viscosity somehow?***

He and Hoseney studied neutral doughs only.

I also do not understand why Brummer says "Anstellgut" is a non-translatable term. *****What do you think it translates as?*****

I take it that this a very ripe starter, very acid, maintained at room temperature at some infrequent rate of refreshment?***** I

s it always rye based?****

Always a high-ash flour?****

How is it different from the type of French and American wheat starters that are refreshed 1:1 every eight hours, or 1:4 every 12 hours?*****

What is its consistency, pH, Total Titratable Acid?*****

My assumption is that my lack of understanding comes from the German use of sourdough as primarily acidification, whereas here we look for a little acidification, a good flavor, and good leavening power.****

Do German bakers ever make wheat breads leavened with higher starter percentages than those Brummer cites, for example 20% or 30% starter?****

Or do they acidify with very ripe starters and leaven with commercial yeast*****

I am curious about the flavor/sensory aspects of the FQ: *****

When a bread is fairly sour (SF Sourdough, some rye breads) is the perceived sourness mostly lactate, mostly acetate, or due to the pH or TTA of the bread?*****

Calvel brings this subject up, but does not resolve it to my understanding. As for your answers to my previous questions, thank you-- I will look this material over again, and let you know if I have questions.*****

Do you mind if I put the text of your letter (with attribution) on the internet as a posting to the newsgroup Rec.Food.Sourdough? I will NOT put your address or email address in the posting, unless you want me to. Please let me know, as I think it might become part of the FAQ file there (Frequently Asked Questions). I will forward your entire letter to a very few people in academia here who have been helping me, so you might hear from one of them.

Dan Wing

-----------------------------

Date: Fri, 14 Feb 1997 15:50:30 +0100 (MEZ) From: Michael Gaenzle To: Dan Wing <Wagons@ConnRiver.net> Subject: Re: sour dough microbiology MIME-Version: 1.0

Dear Dan Wing!

I do not mind if the answer is posted to the rec.food.sourdough: I've also been browsing in that newsgroup.

To answer a few of your questions:

I) There is no rye bread without acidification of the dough. Rye flour does not contain gluten (or a different type of gluten that does not have the gas-retaining properties), so that the structure of rye bread relies mainly on gelatinized starch. Rye flour does have a higher amylase activity than wheat flour, furthermore, the gelatinization temperature is a few degrees lower than that of wheat starch. Thus, with the temperature optimum of rye amylase being about 50 - 52C (with substantial activity up to temperatures of 70C) and starch gelatinization starting at 55C, starch is degraded during the baking process UNLESS the amylases are inactivated by lowering the pH below 4.5. The situation is exacerbated if there was wet weather during the harvest, as germinating rye has higher amylase activities and the starch granules are damaged, thus facilitating hydrolysis.

II) "Anstellgut" is more or less the same as the continuously propagated wheat starters of the SF sour dough bread, so no harm is done if it is translated as "starter sponge" or something like. German sourdoughs usually are rye based for two reasons:

1) Due to the climatic conditions in Germany, especially in the northern and eastern parts that make it difficult to grow wheat, rye flour is just as important for bread production as wheat flour.

2) As these is no necessity to acidify wheat flour (though it enhances the flavor), most bakers do not use sour dough to produce wheat bread. Starter sponges are not necessarily propagated separately. If the dough is taken care of according to traditional methods, it is re-inoculated three times to produce bread dough (reading Bruemmer and Spicher, you probably have already encountered the "three stage sour dough method." A part of the bread dough is used to prepare the sour dough for the next day. This makes 3 - 4 inoculations a day, the ratio of sour dough to fresh dough being approximately 1:3. One has to make a point of it: there is no typical sourdough without continuous propagation! The microflora of these rye starters is actually the same as for wheat starter in SF or Italy: Lactobacillus sanfrancisco and Candida milleri or Saccharomyces exiguus. The pH of a ripe sour dough will be between 3.6 and 4.0 (L. sanfrancisco does not grow below pH 3.6). The total titrable acidity (TTA) depends on the flour employed: as the lactobacilli acidify to pH 3.6, flours with high buffering capacity (amount of acid required to lower the pH), e.g. whole flours, have a higher TTA than white flours with a low buffering capacity. Furthermore, if "hard" water with high concentrations of Me2+ CO3- is used, the TTA will be higher.

3) Acidification vs. leavening: As mentioned above, rye flour or mixtures of rye and wheat flours containing more than 20% rye must be acidified in order to get bread. As the propagation of sour dough is very time consuming if the full leavening capacity of the organism is to be obtained, quite a few processes have been developed in Germany that ensure that the dough is acidified (or that the sour dough added to the bread dough contains enough acid to bring the pH of the bread dough below ca. 4.5), but no leavened by the sour dough microflora. Leavening is achieved by bakers yeast. Basically, there are three possibilities:

1) Dried sourdough with a high TTA (>20) is added to the bread dough, there are no lactobacilli involved in the fermentation (sometimes they are present in the dried sour dough preparation anyway, as in Germany, something called sour dough must contain viable lactic acid bacteria. The dried dough is sold much more readily if it can be called sourdough).

2) A sour dough is kept at room temperature for up to one week. The TTY of that dough is high enough to use it for baking, but as the organisms are rather stressed in such an environment, they will not contribute to the leavening of the dough. Such doughs do not contain lactobacillus sanfrancisco, but other lactobacilli that are more acid tolerant (the ph of such a dough reaches 3.4 - 3.6 after one day, and stays there for the four or five more days that the dough is kept).

3) One stage or two stage processes with starter sponges. One or two stage processes usually do not ensure that the lactobacilli in the dough are fully metabolically active if the bread dough is prepared, thus, the leavening capacity is rather poor, but enough acid has been produced. As far as I know (I never made a survey, though), only few bakers make bread with traditional processes without bakers yeast added to leaven the dough. Acidification of the bread dough with sour dough is rather common, and the sensory quality of such bread is quite close to that of bread made without bakers yeast. Straight processes with bakers yeast and chemical acidification (citric, lactic, and acetic acid, or mixtures thereof) are also quite common to produce rye bread.

4) Lactic acid and acetic acid will change taste and flavor of bread beyond the decrease of pH: the taste buds (sour, bitter, sweet, salty) are on the tongue, any other aroma is perceived with the nose; therefore, the aroma compounds must be volatile. Acetic acid is more volatile than lactic acid, thus, it's impact on the flavor is more pronounced than that of lactic acid. Spicher says that a ratio of 20 acetate to 80 lactate is optimal. It must also be taken into account, that the lowering of the pH influences the formation of other aroma compounds during the baking process. The acetic acid is furthermore important as growth of spoilage organisms such as molds or rope causing bacilli (Bacillus subtilis) is inhibited by high acetic acid concentrations.

I hope that I could answer your questions

With kind regards

Michael Ganzle

-- Darrell Greenwood, Vancouver, BC Darrell_...@mindlink.net My web homepage... http://mindlink.net/darrell_greenwood/

slki...@aol.com

5/2/98

For some reason, neither of my two servers is showing this post after a few days, so I am re-posting. Sorry for the duplication...

Sam

------------

All,

I did a little Internet snooping and came up with a few things I thought were relevant/ interesting...

I have taken the following quotes from a sub-page of http://www.phys.ksu.edu/pub/gene/chapters.html -- an interesting site on yeast genetics. Their data concerns standard bakers' yeast, but I think much of it is applicable.

> The growth behavior of yeast cultures is similar to that of bacteria. When a growth medium is inoculated, the cells require a period of preparation before they start dividing. Following this lag period which may be up to several hours they rapidly enter the exponential phase during which their number and mass double at equal time intervals. After a period of growth at a relatively constant exponential rate, some environmental condition becomes growth limiting so that the rate of increase diminishes and growth eventually stops. The population and mass become constant. The culture remains stationary and the cells remain viable for several hours; if the culture is refrigerated the cells remain viable for months. Eventually the cells die, and at room temperature or warmer they will undergo autolysis: their own digestive enzymes become active and they literally digest themselves, reducing their proteins and nucleic acids to their simpler components; they produce a particularly unpleasant stench in the process.

This tells us a lot of things. For me, one of the most interesting was that the yeast (in our case we could reasonably include bacteria as well) does, in fact, reach a stable population. It is not simply an either/or case where the population is either growing or dying off. In fact, their text seems to indicate that the microorganisms in a refrigerated starter remain at high concentration for quite a while (months) after maximum population density is reached.

The second thing, that I am kicking myself for not remembering earlier, is autolysis. This phenomenon somewhat supports Dick's idea that proteolytic enzymes are released primarily after fermentation slows down. However, this assumes that that the yeast have reached the point of starvation, and I doubt that this happens during the fermentation of a dough.

Further, as mentioned above, autolysis produces a distinctive and very unpleasant odor and flavor. I am familiar with this from my brewing and it's hard to miss. So, I imagine that autolysis isn't a major cause of protein degradation during a sourdough rise. On the other hand, this might be of concern in a thin unrefrigerated starter.

They also say:

> Normal yeast can grow either aerobically, in the presence of oxygen or anaerobically, in the absence of oxygen. Under aerobic growth conditions they can support growth by oxidizing simple carbon sources, such as ethanol, acetate or glycerol. If they have adequate oxygen, they will completely oxidize their carbon sources, usually sugars, to carbon dioxide and water. However, under anaerobic conditions, deprived of oxygen, yeast can convert sugars only to carbon dioxide and ethanol, recovering less of the energy. In either case, growth will be limited by some essential nutrient or the accumulation of the toxin.

> > Yeast grow equally well in liquid media or on a nutrient surface such as an agar plate or an exposed surface of some kind of food. In liquid they must be stirred or shaken if they are to remain aerobic; otherwise, they settle to the bottom of the container, consume the dissolved oxygen, and grow anaerobically.

More data later...

Sam Kinsey slki...@aol.com

slki...@aol.com

5/1/98

A few tidbits from the American Association of Cereal Chemists. Their site is at http://www.scisoc.org/aacc/ and their publication is called "Cereal Chemistry."

--------

> Determination of Yeast Growth in Doughs. Thorn et al. CChem 37:415 (1960): Yeast cells were quantitatively recovered from dough by a process in which...

Dick had speculated earlier that the scientific data on microorganism growth in a dough (as opposed to in liquid or some other medium) might be sparse due to the difficulties inherent to the medium. Since they have been doing it with yeast for around 40 years, probably not true.

--------

> Effects of Proteolytic Enzymes on Gluten as Measured by a Stretching Test. Kruger. CChem 48:121 (1971): The stretching characteristics of gluten are found to be changed markedly upon incubation with proteolytic enzymes... Increasing concentration of enzyme caused a progressive decrease in gluten consistency.

--------

> Effects of Acid-Soluble and Acid-Insoluble Gluten Proteins on the Rheological and Baking Properties of Wheat Flours. Preston et al. CChem 57:314 (1980): Gluten was fractionated into acid-soluble and acid-insoluble protein fractions... The dough-strengthening effects obtained when gluten proteins were added were mainly due to proteins present in the acid-soluble gluten fraction, whereas the acid-insoluble gluten proteins at higher levels had a slight dough- weakening effect... Addition of increasing levels of gluten to the base flours significantly increased loaf volume... Similar increases in loaf volume were also obtained by addition of the acid-soluble gluten proteins. Addition of acid-insoluble gluten proteins significantly reduced loaf volumes

This was very interesting, in that it seems to indicate that the presence of acid can have a marked affect on the quality of the gluten. This is further supported by the following article.

> Effect of Strength and Concentration of Acid on the Functional Properties of Solubilized Glutens of Good- and Poor-Quality Bread Flours. Goforth et al. CChem 54:1249 (1977): Acid solubilization was detrimental to loaf volume at pH values below 4 for glutens from good- quality flours and at pH below about 4.85 for glutens from a poor-quality flour. Impaired loaf volume was attributed to diminished hydrogen bonding caused by cleavage of amide groups from the gluten proteins during solubilization in acid.

With respect to sourdough breads, the following study is relevant to this topic.

> Rheological Dough Properties as Affected by Organic Acids and Salt. Galal et al. C Chem 55:683 (1978): A combination of organic acids isolated from San Francisco sourdough and NaCl profoundly affected dough properties. Mixing time and stability of dough were greatly decreased when organic acids alone were added. Salt had the opposite effect, however, it increased mixing time and dough stability.

--------

Another affect of acid on doughs is the activity of various Proteases at various pH.

> Rheological Changes in Cracker Sponges During an 18-Hour Fermentation. Wu et al. CChem. 66:182 (1989): The pH of cracker sponges was the most effective in reducing their resistance to extension. The effect was attributed to proteolytic enzymes, because the optimum pH of 4.1 coincides with the reported optimum pH of indigenous flour protease.

--------

It also looks like proteolytic enzymes are, in fact, a relatively significant constituent of bread flour.

> The Proteolytic Enzymes of Wheat and Flour and Their Effect on Bread Quality in the United Kingdom. Hanford. CChem 44:499 (1967)

> The Proteolytic Enzymes in Wheat Flour. Wang et al. CChem 46:537 (1969)

> Properties of Wheat Flour Proteinases. McDonald et al. CChem 41:443 (1964): Self-digestion of flour showed a pH 4.0 optimum... Both dough-mixing and the presence of sodium chloride substantially reduced the proteolytic activity of flour.

--------

> Influence of Starter Cultures Consisting of Lactic Acid Bacteria and Yeasts on the Performance of a Continuous Sourdough Fermenter et al. CChem 69:20-27 (1992): [Experiment used] eight pure cultures of lactic acid bacteria... The performance of the fermenter can be improved and stabilized by adding starting cultures of yeasts isolated from sourdoughs... Fermenting sourdoughs with added yeast showed a significantly higher acid formation than did those without (P greater than 95%) added yeast. The accelerated acid formation was due almost entirely to additional production of acetic acid. This effect was independent of the strain of yeast.

This is an interesting insight into output side of the relationship between bacteria and yeast in a sourdough. I find it interesting that the presence of yeast increased acetic acid (which isn't really the kind we want, is it?).

--------

> Lactic and Volatile (C2-C5) Organic Acids of San Francisco Sourdough French Bread. Galal et al. CChem 55:461 (1978): Changes were observed in the pH, total titratable acidity (TTA), and lactic and volatile (C2-C5) organic acid contents of commercially prepared sour starter sponges, bread doughs, and fully baked bread. The results showed that lactic and acetic acids composed most of the total TTA. Gas-liquid chromatography, however, showed that six other minor acids (propionic, isobutyric, butyric, alpha-methyl n-butyric, isovaleric, and valeric acids) contributed to the TTA of the fully fermented starter sponge, the fully proofed bread dough, and the baked bread (1.19, 0.64, and 0.59%, respectively). Baking increased the pH negligibly but decreased the TTA by 9%, mainly due to the loss of acetic acid.

> The Acetic Acid Content of Sour French Bread and Dough as Determined by Gas Chromatography. Hunter et al. CChem 47:189 (1970): The total acidity of sour French bread, dough, and starter was determined... The results were compared conventional bread and dough. There was ten times more acid in the sour bread than in the conventional bread. Percentage of acetic acid present in the acid fractions was determined by gas chromatography. Approximately half of the total acidity of sour French bread and three-fourths of the total acidity of conventional bread was acetic acid.

--------

Sam Kinsey slki...@aol.com

Long Technical Posts, Parts 1, 2, 3, 4

Edited 10/14/16 by Sourdough@CarlsFriends.net (Mary Buckingham) format html file, corrected spelling

-Surface Links-