Experimental cookery

Fermentation. The production of gas in the dough to render the bread porous is known as fermentation. Both yeast and bacteria are used to pro- duce gas, bacteria producing the gas in salt-rising bread, yeast in ordinary bread. Microorganisms in breadmaking. Fuller states that the "microorganisms associated with the production of bread may be divided into three main groups: (1) the yeast Saccharomyces cerevisiae, carefully purified and selected strains of which are purposely added to the dough; (2) certain bacteria, which, introduced either purposely or accidentally, assist in the development of the gluten and give rise to characteristic flavoring products ; and (3) the unwanted organisms, B. mesentericus, torulae, and moulds, which are introduced chiefly from flour, air, and perhaps water, uninten- tionally either into the dough or onto the baked loaf." Fuller states that it seems likely that attention has been confined too much to selecting and purifying yeasts in relation to their carbon dioxide producing powers and that side reactions, i.e., bacteria-producing, essential flavoring ingredients have been neglected. He cites the work of a Russian microbiologist who examined the bacterial flora of a number of samples of *'leaven." The dominant organism in all was Lactobacillus panis acidi, with Streptococcus lactis acidi and others in small numbers. Adding Lacto- bacillus panis acidi to yeast gave a bread with flavor superior to that of bread in which yeast alone was used. Enzyme action in fermentation. The yeast contains an enzyme, zymase, that produces carbon dioxide and alcohol from the sugar. During fermenta- tion many changes are occurring in the dough. The flour enzymes as well as the yeast enzymes bring about definite reactions. The chief amylolytic enzyme of the flour, diastase, produces maltose from starch. Flour contains some initial sugar but this is used up in gas production and it is essential for sugar to be formed for new gas production. Yeast also contains some diastase. Sugar is usually added to bread dough. It is not essential, but fermentation is more rapid. Most flours contain sufficient diastase for bread making, but in some the diastatic activity is weak. Commercial bakers may add diastase preparations to dough made of flours weak in diastase to shorten the fermentation time. Sugar is often added in rather large quantities in home-made bread and it, plus the sugars already present in the flour, plus the sugar formed by the diastase during fermentation, furnish the sugar for the action of the zymase to produce carbon dioxide. The proteinases hydrolize a part of the protein, and if very active may cause harmful results. For, if the gluten, which during the first part of fermenta- tion may be too tenacious, becomes too soft or thin the volume of the loaf may be diminished and the texture impaired. Balls and Hale say a little 432 FLOUR AND BREAD proteinase is beneficial. J0rgensen states that yeast water stimulates the activity of proteinase.