A Hands On Activity
Yeasts are unicellular organisms. They reproduce by
budding, and can be activated in the classroom.
|Zip-lock plastic sandwich bags
|Packages of Yeast
|Heating pad or hot water bottle
Each group receives a zip-lock bag.
Pour about a third of a cup of warm water into the bag.
Add three or four teaspoons of sugar. Seal the zip-lock
Shake sugar and water together until the sugar is dissolved.
Open the bag and add about a half a teaspoon of yeast.
Push as much of the air as possible out of the bag. Seal the
Set the bag aside and let the yeast go to work.
Yeast grows quickly in water that feels a little warm.
If the water is colder, the yeast will grow more slowly. If the
water is too hot, it will kill the yeast.
The flat shape of the plastic bag has a lot of area in proportion
to its volume. It will come to room temperature quickly. If you
want the yeast to work more quickly, you may want to wrap it
in a towel and put it on top of a heating pad or hot water bottle.
Be careful not to get the yeast too hot, as too much heat will
If the room is cool and you have no way to keep the yeast
culture warm, wait until next morning to see the bags puff up!
As the yeast works, it will break down the sugar. About 45%
of the sugar is broken down into carbon dioxide. The rest is
turned into alcohol. The yeast cells will grow and bud, producing
Yeast will stop growing when it has used up the sugar or when
the alcohol level reaches about 14 % of the liquid.
Now that you have a yeast culture started, you can stir in
some flour and see how it makes bubbles in the dough. You could
also pour the yeast starter into a plastic bottle, add some more
water and sugar, and seal the bottle by putting the mouth of
a balloon over the mouth of the bottle. As the yeast works, it
will blow up the balloon. When fermentation stops, the balloon
will gradually shrink again.
© Elizabeth Anne Viau, 1999. This material
may be used freely for instructional purposes but not sold for
a price beyond the cost of reproduction. Please inform the author
if you use it at firstname.lastname@example.org.
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