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46. What's all this about natural leaven?

46. What's all this about natural leaven and L. sanfranciscensis?

Dan wrote: "I chose to write "natural leaven" because it is less awkward than 'mixed ferment cultured from the environment and sustained with repeated inoculation.'" -- Dan

Michael replied: "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 Òsustained 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, whereever L. sanfranciscensis comes from, it most probably does not come from the flour.


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 mentionned 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 Bšcker company told me that it takes about two weeks of repeated inoculations to get a good "sanfranciscensis" 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.

-- Michael


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