Download Alternate Bad Germs Yeast Experiments

Student Activity Sheet
Alternate Bad Germs Yeast Experiments
Lesson 4
Alternate #1 – Clemson University Extension
3 small dishes
Water
Ice
Yeast
3 packets of yeast
Put ¼ cup of lukewarm water in 1st dish, ¼ cup boiling water in 2nd dish, and
¼ cup ice water in the 3rd dish. Read the yeast label to see if you need to add
sugar to help yeast grow.
In a few minutes you should have dramatic evidence that yeast grows faster
at room temperature than at hot or cold temperatures. This is because you
started with billions of live yeast cells, and at the right temperature yeast
produces a lot of gas (carbon dioxide) that makes it bubble and rise. It
demonstrates how fast “germs’ can grow.
Most bacteria do not produce gas to bubble and rise and most foods do not
have as many bacteria on them as the amount of yeast that you started with,
but it also takes fewer bacteria to make people sick.
Alternate #2 – Patty Garcia, Norman County Extension
3 glass jars with lids
Sugar
Hot water – over 140 degrees
Ice water
Yeast
Thermometer
Warm water – 110 degrees
Place 1 tsp. Of yeast and 2 tsp. Of sugar in each jar.
Microwave or heat 2 cups of water to over 140 degrees.
Add 2 cups of ice water, 2 cups of the hot water and two cups of warm water
to each jar. Cover, shake well and then UNCOVER all three jars to prevent
explosion. In about 20 minutes, observe rate at which the “bacteria” has
grown or not grown and why.
Free yeast and disposable strip thermometers may be available from the Red
Star Yeast Company.
Safe or Sorry-Food Safety Program of the Minnesota Department of Health, Environmental Health Division
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