How do yeast cells make alcohol and cause bread to rise?

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Accepted Answer

Hi, everybody. Let's take a look at our next question. It says what happens when baker's yeast acts on sucrose during bread making a sucrose gets transformed directly into lactic acid causing do expansion. B. Yeast hydrolyzes sucrose producing fructose which then turns to Glycerol C yeast ferment sucrose resulting in acetic acid contributing to flavor enhancement. Or D yeast first hydrolyzes sucrose producing monosaccharide which are then fermented, releasing Co2 and causing dough rise. So let's think about what's happening here. When we have East Plus Sus, we recall that sucrose is a dy saccharide consisting of one molecule glucose and one molecule of fructose. While yeast is capable of fermenting both of these sugars. And our answer here is going to be choice D that yeast first hydrolyzes sucrose which produces the monosaccharide glucose and fructose. These are fermented. The fermentation process releases carbon dioxide. The carbons here are converted into ethanol in that f fermentation process. We're not used to thinking of ethanol, alcohol in the context of bread making. It gives a little flavor enhancement to the bread and then evaporates during the baking process. The carbon dioxide that's released is uh trapped in the gluten protein network of the dough gluten is a very stretchy protein. So all that trapped carbon dioxide stretches out, the gluten causes the dough to rise and gives bread that fluffy texture. Let's look at their answer choices to understand why they're not correct choice. A sucrose gets transformed directly into lactic acid. Um This is the lactic acid fermentation pathway. This is not the fermentation pathway used in bread making. This is that fermentation pathway used by, for instance, muscle cells when they run out of oxygen and like it is an anaerobic process, it produces some a TP to keep things going uh until more oxygen is available. So wrong fermentation pathway in choice. A whereas B yeast hydrolyzes sucrose. Well, that is correct producing fructose which shrinks to glycerol. Well, this is not the pathway. As we saw, it produces fructose and glucose and they're converted into ethanol and carbon dioxide. The choice c yeast ferments sucrose resulting in acetic acid contributing to flavor enhancement. The production of acetic acid is a second step. Um You have fermentation, anaerobic fermentation that goes to ethanol, which is the process we're talking about in bread making if you wanted to produce vinegar rather than ethanol. Uh Louis Pasteur showed that there was then a second step which is aerobic fermentation using oxygen by bacteria. So the first step is done by yeast. The second step by bacteria and that produces acetic acid from the ethanol, but that's not what's going on in the bread. So that's not our correct answer. So once again, what happens when baker's yeast acts on sucrose and bread making choice. D yeast first hydrolyzes the sucrose producing monosaccharide which are then fermented, releasing carbon dioxide and causing dough rise. See you in the next video.

How do yeast cells make alcohol and cause bread to rise?

Verified Solution

Key Concepts

Fermentation

Yeast Metabolism

Leavening