yeast

[mimififi]

Hi,
can anyone explain to me how yeast works? I'm after a chemicular explanation and a why and how it does what it does to bread.

many thanks
mimi

[Clanad]

Fermentation is the key word, mimi... The yeast (Saccharomyces cerevisiae), is a single celled microscopic fungus that converts the complex carbohydrates in the bread recipe's flour into simple sugars that it feeds on. With an almost instant action it starts to release carbon dioxide and alcohol, all very important by-products in bread-making.The alcohol, by the way, from the fermentation process evaporates off during baking. When protein, starch, and fat molecules break down into their building blocks during fermentation, it breaks down large molecules into smaller, flavorful ones.-- proteins into amino acids, starches into sugars, or fats into free fatty acids. Yeast generates carbon dioxide which makes the dough rise. (Some thanks to Baking 101)
Same process makes the carbon dioxide bubbles in beer and champagne...

[mimififi]

Cool, cheers Clanad, that is a very helpful explanation. Do you know how they make the fast action dried yeast?

cheers
mimififi

[Clanad]

My book says "The particle size of Instant Active Dry Yeasts are finely granulated to allow complete hydration of the yeast cells during the mixing process. As a result, instant yeast becomes active the "instant" it contacts moisture. When using Instant Active Dry Yeast, the bread recipe only needs one rise. The first rise is replaced by a ten minute rest. You don't need to "punch the dough down" afterwards. The second rise takes place after the dough has been shaped. It takes about an hour or so in a warm place or in the refrigerator as a slow rise, until the dough is just about doubled in bulk.While Instant Active Dry Yeast is especially suited to the types of breads typically made in bread machines, it also works for general hand baking. However, avoid rapid rise yeast when you want to develop flavor in the bread through long rising times - according to some bakers, the flavor of the bread does not develop and the texture may suffer because of a fast rise.
A Baker friend of ours says the alcohol developed during the yeast fermentation is actually responsible for a lot of the flavor in bread or rolls, even, as mentioned, most or all bakes off...

[mimififi]

cool Clanad, that's great. I shall be able to go into this chapter in our book now a little more confidently. I hate it when the kids get older and you get a bit stumped over their chemistry questions! 3rd grade is ok, my daughter is in 6th grade and her work is kind of ok most of the time, but keeps me on my toes. I never studied science past GCSE, I did an English Lit course, so I think I've learned more from doing Home Education than the kids have, haha.

Anyway, I really appreciate your help Clanad, I'm very grateful for the time you take in answering my (and others'( questions.

Cheers.

[Clanad]

I may have already mentioned that my youngest daughter home schools her four... full time job and I admire anyone who takes on that challenge...

[mimififi]

All the best mums do, tee-hee!

It's a sterling work and so rewarding.