pH plays a significant role in the production of both yeast-raised and chemically leavened bakery products.

In bread production, it exerts its principal effects during fermentation where it controls yeast activity, amyloltic action, gluten characteristics and the survival of rope-producing organisms. In normal practice, a pH of 5.1 to 5.4 is generally accepted as being conducive to the production of a desirable crumb in white bread. This requires that the final pH value of the sponge or of the liquid ferment be between 4.5 and 5.1 to yield doughs with pH values between 5.0 and 5.2 (Reed 1965).

Some specialty bread such as French or sourdough styles have sharp, tangy sour flavors and will have a pH as low as 3.8 to 4.0 (Maselli and Pomper 1960). When making rye bread by using natural sours, the pH of the sour affects the ultimate flavor, volume, crumb and texture of the baked loaf and should be maintained within an optimal range of 4.2 to 4.5 (Mathason 1977).

The curve shown in Figure 1 (Selman 1948) charts the course of pH in bread production. This particular study employed a lean formula and the sponge-and-dough method. The pH decreased during the sponge fermentation from an initial value of 5.3 to 4.7, with the more rapid decrease occurring during the first two hours of fermentation.

The addition of the dough ingredients essentially neutralized the acidity formed during sponge fermentation, and the pH returned close to its initial level of 5.3. Subsequent dough fermentation during floor time, the intermediate proof and the final proof again increased the acidity, lowering the pH to a level of about 5.0. After baking for 30 minutes, the pH increased to 5.4.

These fluctuations in pH value during the course of breadmaking can be attributed to the effects of yeast fermentation and heat. The acids produced by yeast during fermentation, principally lactic, acetic and succinic acid, may logically be expected to lower the pH of the dough since they show some degree of disassociation. Upon remix of the sponge, the addition of fresh ingredients neutralizes the acidifying effect of sponge fermentation by the introduction of buffering ingredients.