47. How does one measure the ph of sourdough, and what is the effect of different ph's?
For sponges and doughs:
*Weigh 15 g of sponge or dough and place it in a polyethylene container.
*Add 100 ml of distilled water to this sample.
*Seal the container and shake until the sponge or dough sample has completely dispersed.
*Place electrode(s) in the mixture and read the pH value.
*After the pH value has been obtained and recorded, slowly add 0.1N NaOH from the buret and stir constantly until a constant pH of 6.6 is obtained. Read the buret and record the number of ml of NaOH used (that is the TTA or Total Titritable Acidity). Take care not to add the NaOH too rapidly to avoid going beyond pH 6.6.
For bread:
*Weigh 15g of bread, excluding the crust, into a clean dry container.
*Add 100 ml of distilled water, seal the container and shake until bread disperses into a semi-liquid mixture.
*Determine and record pH and TTA as described for brew.
Some useful information for all you "sourheads" out there:
Overmatured sours, i.e., replenished sours matured over 8 hours at 77F, may build up excessive acidity and the lactic acid bacteria will start to inhibit the propagation of yeast cells, i.e., slowing the leavening activity in the sourdough.
A good and fully matured functional sour has a pH of 3.9-4.1 and a total titratable acidity (TTA) of 13-15 ml. Sours that develop acidity equal to a TTA of 18-22 ml or higher with a pH of 3.8 or lower will gradually lose their ability to produce enough carbon dioxide to leaven bread loaves. Having a high acid content also makes doughs softer and makes their cell structure break down during rounding and moulding. This tends to result in an irregular cell structure with thicker cell walls in the bread crumb and a tougher bite. This effect is intensified in doughs with a relatively high water absorption (over 62% of flour weight). However (for all you artisans out there), bread of this type is acceptable as "signature" bread served in restaurants or for personal use or for artisan type bakeries.
Other useful information concerning industry "normal" pH and TTA in breads and their process:
Sourdough starter
3.9-4.1 pH
14-16 TTA
Mixed dough
4.6-4.8 pH
5-7 TTA
Proofed dough
4.2-4.4 pH
9-13 TTA
Crumb
4.3-4.5 pH
6-7 TTA
*TTA values are expressed as ml of 0.1 N NaOH per 20g sample (sourdough starter containing 47.6% flour) titrated to pH 6.6
**This is according to the American Institute of Baking, and not the FDA, so I imagine that would explain some differences in "normal" pH readings.
-- Dave
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