Hi
Yeast likes an acidic enviroment (it help the yeast activate).
AcidificationDough fermentation, in addition to generating alcohol and carbon dioxide, also produces small amounts of a fairly large number of organic acids. These include lactic, acetic, succinic, propionic, fumaric and pyruvic, butyric, isobutyric, valeric, isovaleric and capriotic acids. Among these, the most prevalent are
acetic, propionic, butyric, isobutyric, valeric, isovaleric and capriotic.
Acetic acid is the most prevalent by far. The production of acetic acid is much higher in breads made with a poolish or naturally leavened than with a straight dough. Calvel speculates that acetic acid acts as a carrier for bread crumb aroma, sensitizing the taster to the other constituents of the aroma. This effect seems to be directly linked to the amount of acetic acid in the dough
As maturation progresses and fermentation is prolonged, the dough becomes richer in organic acids, and this increase becomes evident as a lowering of its pH. The longer fermentation is allowed to continue, the richer in organic acids the medium becomes. This formation of acids is reflected in a time-dependent decrease of pH and an increase in titratable acidity in the fermenting medium. A number of factors such as aroma, and keeping quality are enhanced as a result of the development lower pH (more acidic) dough. Temperature of the dough is an important factor. Calvel demonstrates this in the graph shown here. (Graph 2)
While progressive pH change in naturally leavened dough is relatively rapid as can be seen, the change appears to occur more slowly in dough leavened with bakers yeast. The presence of salt in dough often masks acetic acid. When the dough is leavened with an unsalted preferment, the acetic acid or vinegar odor appears a little more rapidly, although it is still hardly perceptible.
The results of these evaluations of dough pH are influenced by leavening method, and are different from one another. The pH is ultimately related to the level of residual sugars present in the dough before baking. Thus, a discussion of pH must, by default, include discussions of residual sugars. These residual sugars are the remainder of those that fed dough fermentation. They fulfill important functions during the baking process. The level at which they are present plays an important role in the quality of the final loaf of bread. Generally, a below average pH coincides with a lack of residual sugars, which translates to a deficiency in oven-spring, i.e. loaf volume, crust coloration and crust thickness, aroma, crust taste, crumb flavor, and keeping quality.
When the dough is leavened with prefemented dough which undergoes an excess of maturation or fermentation, it is good practice to remedy the lack of residual sugar in advance by adding from 0.1% to 0.2% malt extract during mixing to reestablish the proper sugar balance.
Excessive residual sugar may also occur, although this is more rare. If this phenomenon is caused by characteristics inherent in the flour it is a difficult occurrence to correct. If excessive residual sugars occur as a result of the manner in which the dough was handled, i.e. an abnormally short first fermentation, or a lack of proper dough maturation, it is more easily corrected.
The presence of an appropriate amount of residual sugars in the dough at the time of baking is extremely important. It insures an active oven spring, assists in dough development, and helps the loaves to reach a normal volume. Appropriate residual sugar levels contribute to optimal crust color, which in turn, according to Professor Calvel, contributes to the exterior appearance, the aroma and the flavor of bread.
Lactic acid, not mentioned by Calvel, but cited as a prevalent acid in white bread by Pyler also survives at some level in the finished bread. The accumulation of lactic acid in fermenting dough is attributable primarily to the presence of the genus Lactobacillus in both flour and compressed yeast. Of the two acids (lactic and acetic), acetic acid is normally found in smaller quantities. It is also weaker than lactic acid, with a lesser degree of ionization, and its effect upon the pH of the dough is correspondingly smaller.
In sourdough breads ("San Francisco Sourdough)", acetic acid represents about 50% of the total acids found, and was five to ten times that found in white (non-sourdough) breads. The pH of fermenting dough is more strongly affected by the presence of ammonium salts in yeast foods, especially if the ammonia is present as the salt of a strong acid such as hydrochloric or sulfuric acid. Yeast readily assimilates ammonia as a nitrogen source.
Yeast - A Treatise - Section IIBest Regards,
David
Hi Daveyboy,
Thanks for posting this! (and the other threads in this GF Pizza section...you've been busy, I see!) The pizza looks great 
Just curious....what function does the cider vinegar serve in the recipe? I've read it's an ingredient in several GF dough concoctions, but can't seem to find an answer as to what exactly it does for the dough.
cheers!
Dave
