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Modernist Bread on 5 Things You Didn't Know About Yeast - Tips from The Kitchn

Modernist Bread on 5 Things You Didn't Know About Yeast - Tips from The Kitchn
From The Kitchn - November 15, 2017

Baking is applied microbiology. That may seem like an odd way to look at it, but it is only a modest exaggeration. All yeast breads and sourdoughs owe their shapes and textures to the actions of microbes, living creatures that are microscopic in size and typically consist of just a single cell.

Despite its size, yeast is a powerhouse of an ingredient. Yeast cells are living, single-celled fungi that behave like minuscule factories that seem to specialize in the production of bubbles and booze, which is one of the main reasons bread is so complex and special. Working with a living ingredient can sometimes be difficult, but having an understanding of how yeast behaves will ultimately help you bake better bread.

1. Yeast are territorialmuch to our benefit.

The carbon dioxide and ethanol that the organisms release are their wasteand also a defense against competitors that find ethanol so off-putting that the substance keeps other microbes from encroaching on the yeast's food supply.

Yeasts use these two different modes to break down and process nutrients in flour in order to extract the energy and raw materials they need to live and grow.

Yeasts begin to respire immediately after coming into contact with food. In bread baking, respiration primarily occurs right after mixing. As long as oxygen is in ample supply and sugar is not, yeasts crank out carbon dioxide and water as byproducts. But if oxygen is scarce or if fermentable sugars are available, the cells ramp down respiration and ramp up fermentation, which causes them to spit out ethanol and even more carbon dioxide.

During the stage that bakers refer to as fermentationfrom the time the dough is mixed to just before bakingyeasts swing between their two metabolic modes each time their environment changes. As a baker kneads and degasses the dough, more oxygen flows into it, so the yeasts can respire for a while. They then switch back to fermenting as the oxygen gets used up and more fermentable sugars become available.

2. You can control fermentation by controlling yeast's environment.

Dough is a complex environment that keeps the eager microbes in check. High concentrations of salt or sugar in the dough create an osmotic pressure on yeast cells that slows their growth and fermentation. That's one of the reasons why accurately measuring these ingredients is so important. Low moisture content has the same effect. As a result, tight, low-hydration doughs take longer to ferment. (So do sweetened and heavily salted doughs.)

Bakers can also stimulate or restrain the growth and fermentation rate of the microbes by controlling the temperature of loaves as they proof. Refrigeration slows down fermentation. Conversely, a warm and humid proofer is like a yeast sauna that's perfect for speeding up fermentation.

3. It's why bread smells so good.

4. Yeast impact the consistency of your dough.

5. One type of baker's yeast can be used for another.

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