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How Yeast Works
by
Dennis Weaver
If you are going to be a
baker, you should know yeast. Yeast is the magic
ingredient of the baking world. It's alive and
master bakers have learned to cultivate yeast
as a living thing in their
and pastry doughs. In this section we will explore
the different types of yeast and learn how to
cultivate yeast in our products to make the best
breads.
Our grandparents used—and many commercial bakers
still use—fresh yeast rather than the dry yeast
that we buy in the store. Fresh yeast performs
marvelously well but is fragile, must be kept
refrigerated, and used right away—hardly the conditions
of today’s carefree baking.
Instead of fresh yeast, most of us use dry yeast,
either instant active dry yeast or active dry
yeast. The difference in the two is how the yeast
cells hydrate or absorb water. Instant active
dry yeast does not have to be hydrated in water
for five to ten minutes prior to mixing as active
dry yeast does. Active yeast is mixed in water,
the particles are dissolved, and the yeast is
allowed to grow until the mixture becomes foamy.
Then it is added to the flour. The cells of instant
dry yeast are porous to absorb water and can be
put directly in the flour without waiting for
the yeast to hydrate. However, so that the yeast
does not have to compete with the sugar or other
ingredients for moisture, it is best to mix the
yeast in only a portion of the flour. A method
that works well is to mix the yeast with about
one-third of the flour to create a very wet batter
where the yeast cells will hydrate easily and
then, add the remaining flour.
And yes, yeast is alive. It is neither plant nor
animal but a fungus. We add it to the flour in
its dormant state and expect it to thrive in our
dough with moisture and the proper temperature.
Under the right conditions, the yeast cells feed
on sugar and multiply. A loaf of bread, ready
to go into the oven, may contain millions of yeast
cells. (The little particles found in a yeast
packet are not yeast cells. They are an agglomeration
of yeast cells mixed with dextrose or starch into
larger balls containing many yeast cells.)
As the yeast cells feed, they expel carbon dioxide
and alcohol. The carbon dioxide gas rises through
the
dough and is captured by the gluten structure
in the dough to form air cells. The alcohol and
other excretions impart a “yeasty” flavor to the
dough. Master
bakers manipulate the ratio of carbon dioxide
to alcohol—usually with temperature and acidity--to
control the rise time and the flavors in the breads.
So how do we nurture these little creatures? Like
most other living creatures they require moisture,
food, and a hospitable environment. In a moist
environment, yeast will grow rapidly. Most of
the time, you will want your
dough as moist as you can handle without being
sticky. A
dough that is too dry will take a long time to
rise because the yeast will not multiply as rapidly
and because the dry dough is stronger and more
difficult to lift.
Yeast feeds on sugar or converts the starch in
the flour to sugar for food. Without the capability
to convert starch to sugar for food, yeast would
not thrive in sugar free breads such as French
bread. Salt impedes the growth of yeast so you
can slow down the rise with salt. Conversely,
you speed up yeast growth with sugar. An extra
half teaspoon of salt will significantly slow
the rise of the dough.
Moist dough between 78 degrees and 80 degrees
is an ideal environment for yeast growth. Since
yeast is very sensitive to temperature, temperature
is a major factor in how fast yeast multiples.
Yeast is dormant and will not grow at 40 degrees
and grows only slowly at 55 degrees. Yeast dies
instantly at 140 degrees. We recommend not using
water warmer than 120 degrees to avoid accidentally
killing the yeast.
A thermometer has been called the baker’s secret
weapon. In all breads, it is very useful to be
able to measure the temperature of the water,
the dough during mixing, and the
as it comes from the oven. In using a
machine, the exact water temperature is critical
to a uniform outcome.
is baked when the internal temperature is between
190 degrees and 210 degrees. As mentioned, the
ideal dough temperature for the proper growth
of yeast is 78 to 80 degrees. At higher temperatures,
the dough may rise too quickly creating a crumbly
texture to the bread. At less, the
will rise more slowly and will have a higher alcohol
content—though some marvelous, complex flavors
can be created at lower temperatures.
Understanding yeast and how it works is an essential
lesson for the
baker.
Copyright 2003-2007,
The Prepared Pantry (http://www.prepraredpantry.com
). Published by permission in the Article
Directory: http://www.articlecube.com
Dennis
Weaver is a baker, a recipe designer, and a writer.
This article is an excerpt from “Ingredients
and How They Work” --available free at The
Prepared Pantry which sells baking supplies
and tools and has a free online baking library.
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