Yeast in bread

The most important uses of yeast in bread-making are as ... 

What are the main functionalities of yeast in bread-making processes Why is compressed fresh yeast still widely used by the industry despite its lower shelf life What is the factor used to convert fresh to dry yeast ... 

The effect of osmotic pressure on yeast activity is of great importance, and is often overlooked. At salt concentrations up to 1.5%, the effect is slight salt concentrations of 2—2.5%, which are common in bread doughs, inhibit yeast activity considerably. Likewise, sugar concentrations above 4% produce apparent inhibition. Consequently, yeast-raised sweet doughs (15—20% sugar), contain very high yeast concentrations. 

Salt is used as an essential nutrient and a flavoring in food. It is also used in products to change their properties. In breads, it moderates the growth of yeast, and strengthens gluten. In ice cream and frozen... 

Sodium propionate is also often used as an antifungal agent. Calcium is often preferable to sodium, both to reduce sodium levels in the diet and because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread, making them available for the yeast, and improving the texture of the bread. Stale bread is caused by the starch amylose recrystallizing. The enzyme a-amylase converts some of this starch to sugars, which helps prevent recrystallization. 

The enzymes in wheat, and hence in flour, that often cause problems in the bakery are present in the seed to make nutrient available to the seed. Similarly, this is why sprouted wheat causes problems if it is allowed to get into flour. Thus, the a-amylase is low in mature wheat grains but rises rapidly on germination. In bread, a low, but not too low, level of a-amylase is desirable since it produces sugars to feed the yeast and opens up the structure. Deliberate additions of malt flour were once common, but are now rarely made, to increase the amylase level. 

Yeast is the leavening agent in bread and yeast raised wafers. Carbon dioxide produced by the yeast not only causes bubbles to form but also dissolves, reducing the pH. The other major product of yeast action, ethyl alcohol, boils away during the cooking phase. 

Soda bread is a chemically leavened bread made in Ireland. Instead of yeast the bread is raised chemically using sodium bicarbonate. The traditional source of acid is buttermilk, which contains lactic acid. The use of cream of tartar is now more common. This prevents the bread becoming too alkaline. 

The baking studies with yeast breads indicate that levels of substitution of up to 15% pea flour or concentrate for wheat flour result in breads that are generally acceptable, but are readily distinguishable from, and less preferred to, wheat controls. 

The yeast used in bread dough feeds on sugar to produce carbon dioxide gas, which causes the dough to rise. Why is bread dough commonly left to rise in a warm area rather than in the refrigerator ... 

Acetic acid (pure and as vinegar) and calcium, potassium, and sodium acetates, as well as sodium diacetate, serve as antimicrobial agents. In the United States, vinegar can contain no less than 4 grams of acetic acid per 100 milliliters of product Acetic acid and calcium acetate are most effective against yeasts and bacteria, and to a lesser extent, molds. The diacetate is effective against both rope and mold in bread. It is interesting to note llial die antimicrobial effectiveness of acetic acid and its salts is increased as the pH is lowered. 

The flavor compounds of the crust from the chemically leavened model bread were then compared to those recently identified (6) in the crust of a standard wheat bread which was leavened by addition of yeast (Table I). One striking difference was that Acp (No. 16), which showed the highest FD-factor in the yeast-leavened bread showed a very low FD-factor in the chemically leavened bread. This indicated, that the flour contained only minor amounts of the precursor (s) for the formation of Acp. On the other hand, 2(E),4(E)-decadienal, 2(E),4(E)-nonadienal, l-octen-3-one and 2(Z)-nonenal, which are undoubtedly formed by a heat-induced oxidative degradation of the flour lipids, became predominant odorants in the chemically leavened compared to the yeast-leavened bread. 

To reveal the contribution of yeast in the formation of the Acp the amount of Acp in a bread crust from yeast-fermented dough was compared to the amount present in the crust of a chemically leavened bread. The production of Acp was reduced from 34 jig/kg to 9.6 jug/kg flour when the yeast was replaced by a commercial leavening agent. 

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