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Science
While You Dine
How Bread Works |
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If
you examine a slice of bread closely, you will see that it is full of
air holes.
This
makes it spongy and soft. Notice, too, that bread is moist.
If
you let a slice of bread sit out on a table for a day you will realize
just how moist fresh bread is!
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Bakers use two facts to make soft, spongy, moist bread:
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First, yeast (a
single-cell fungi) will eat sugar, and from the sugar
create alcohol and carbon dioxide gas as waste products. The
carbon dioxide gas created by yeast is what gives bread its airy
texture. The alcohol, which evaporates during baking, leaves
behind an important component of bread’s flavor. |
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Second, wheat flour when mixed with water and kneaded
becomes very elastic. The mixture becomes stretchy like a balloon
because of a protein in wheat known as gluten. Gluten gives
bread dough the ability to capture the carbon dioxide produced by
yeast in tiny flour balloons. |
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Those Gas-y Yeast Cells!
Try this experiment to make carbon dioxide from
yeast.
What You Need:
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One large Ziplock
Freezer Bag |
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One envelope
Rapid-Rise Active, Dry Yeast |
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One cup lukewarm
Water (When you stick your finger in it, it should feel neither
warm nor cold). |
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˝ cup Sugar |
What You Do:
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In a bowl, mix the
water and the yeast. When you pour the yeast granules into the
water, you activate the yeast cells. |
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Mix in sugar. |
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Pour the entire
mixture into the plastic bag. Squeeze and push as much air as
possible out of the bag. |
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Seal the bag
tightly. |
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Put the plastic bag
in a warmish place. Come back in about an hour. |
When you come back to your experiment,
you’ll notice that yeast cells do a really good job of creating carbon
dioxide. You will see that the bag has partially filled with the gas,
and that the liquid is full of carbon dioxide bubbles that the yeast
produced. A yeast cell can digest approximately its own weight of sugar
(glucose) per hour. From the glucose, yeast produces two
molecules each of carbon dioxide and alcohol (ethanol). Although
yeast cells are very small, a packet of yeast contains billions of them.
You should be able to see a noticeable amount of puffiness in you bag
after 2 hours. It will get quite puffy if you leave it sit overnight. |
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