Sour Dough Making

In sour dough making (lowering the pH to 4.0-4.3) rye flour acquires the aroma and taste properties so typical of rye bread (cf. 15.1.5). 

Yeast (Saccharomyces cerevisae, Saccharomyces minor and others), which are mainly responsible for dough leavening, and a complex bacterial flora in which lactic acid-forming organisms dominate Lactobacillus plantarum, Lactobac, San Francisco and Lactobacillus brevis) are present in sour dough. 

Sour dough is prepared by various procedures which differ considerably in the length of time required (Fig. 15.38). A three-stage procedure takes into account the optimum temperature and humidity needs of yeast and bacteria. Yeast prefer to grow at 26 °C, while the bacteria of interest grow best at 35 °C. 

In setting up a three-stage process, initially an aqueous flour suspension is inoculated. This is the first full sour build-up stage (Fig. 15.38). After maturation, further amounts of flour and water are added and the process is continued with a basic sour stage at 35 °C and then, in a similar way, continued with an additional full sour third stage at 26 °C. 

The incubation conditions given in Fig. 15.38 are only the essential outline. Temperature deviations influence the spectrum of fermentation products. 

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While it is always possible to make a sour dough by leaving some flour and water to acquire suitable micro-organisms a working sour dough bakery would keep its own culture going by holding back a portion of the culture. 

Rocken, W. and Voysey, P.A. 1995. Sour-dough fermentation in bread making. J. Appl. Bad. Symposium Suppl. 79, 38S-48S. 

A dough mixed at a high temperature will develop undesirable ferments which cause sourness and will make an unsatisfactory loaf in general. These results are due partially to the fact that the yeast cannot produce the proper fermentation when subjected to such unfavorable temperatures. The gluten in the flour will also be softened and deteriorated to such an extent as to seriously affect its gas retaining power and cause it to absorb from one to three per cent less moisture. 

Like all acids, carboxylic acids taste sour. The most familiar carboxylic acid is ethanoic acid, better known by its common name, acetic acid. Acetic acid is the active ingredient in vinegar. It can form by the oxidation of ethanol, which is why wines left open to air become sour. Some yeasts and bacteria also form acetic acid when they metabolize sugars in bread dough. These are added to bread dough to make sourdough bread. Other common carboxylic acids include methanoic acid (formic acid), present in bee stings and... 

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