This section is from the book "A Treatise On Flour, Yeast, Fermentation And Baking Together With RecipesFor Bread And Cakes", by Julius Emil Wihlfahrt. Also available from Amazon: A treatise on flour, yeast, fermentation and baking, together with recipes for bread and cakes.
Generally speaking, the characteristic acid in the wheat flour is given as lactic acid and, for convenience, the acidity is expressed as percentage amount of lactic acid.
Wheat flour, when fermented with yeast, increases in acid contents in direct proportion with the quality of the yeast employed and with the temperature of the dough.
The percentage amount of lactic acid in a good flour is termed at 0.09 per cent and this percentage amount of acid consists, as far as is known in this direction, of 95% lactic, 4 1/2% acetic and 1-10 to 1/2% of butyric acid.
Acids contained in this proportion in flour have beneficial influences, both for flavor of bread and assistance in fermentation.
During the process of fermentation the lactic acid increases the quickest and the acetic acid very slow; that is to say, if the dough is properly manipulated.
The increase of acid during fermentation is produced by bacteria, and these acids are known as organic acids.
Again, they do not affect doughs alike, as much depends upon the temperature of the dough.
A dough at too high a temperature will develop acetic acid very rapidly, and too much of this acid will cause an over percentage of butyric acid, which means bad results and likely sour bread.
The lactic acid, always present under normal conditions, unlike the acetic acid, will increase too rapidly in a dough at too low a temperature. Lactic acid, while greatly beneficial in a dough when present in the right proportion, is also detrimental when present in too large a quantity, as too much of it will assist the acetic acid to grow too rapidly, and what effects this has upon the bread are visible in the foregoing.
x\nother main factor to be considered is the influence the quality of the yeast used has upon the acidity of the doughs. Bad yeast - yeast that is either too weak in strength or one with too much acid contents - will increase the acidity of the dough too rapidly; thus showing why a well-proportioned yeast should be used.