## What do yeast like to eat?

By Marshall Brain

In the video, we used little envelopes of yeast that you can get at any grocery store, and we fed the yeast different foods to see what yeast likes to eat. By putting the yeast into zip-lock bags, we can measure the amount of carbon dioxide gas the yeast produce. The yeast will produce the most gas with the foods that they like best.

If you want to try some yeast experiments at home, here's what you need:

• Some 1-gallon zip-lock plastic bags
• Little envelopes of yeast (or a jar of yeast and a teaspoon)
• Some cups to mix the yeast and water in
• A 1-cup measuring cup
• Some different foods - things like sugar, apple juice, soda, birthday cake, ice cream - whatever you want to try.
Let's say you are going to do four experiments. Get four zip-lock bags, four cups, four packages of yeast and your four foods.

Step 1: In a cup, mix one envelope of yeast in one cup of warmish water. Not hot water - that will kill the yeast. Warm is what you want. Stir it up with a spoon so all the yeast dissolves. [A good experiment you might try on your own: how warm does the water need to be to kill the yeast? Use a thermometer and try different temperatures in each bag (like 100, 120, 140...). Feed all of them sugar and see what happens.]

Step 2: Pour your yeast-water mixture into a zip lock bag.

Step 3: Add your food. If you are using a solid (like flour or sugar), use 3 teaspoons of the solid. If you are using a liquid, use 4 ounces.

Step 4: Get all the air out of the zip-lock bag and then zip it shut.

Step 5: Wait about two hours, and then look to see which bag has the most gas in it. The bag with the most gas contains the food that yeast like best!

Some things to try: Does it work better if you put the bags in a warm place or a cold place? What happens if you let it sit 4 hours instead of 2? If you give the yeast 10 teaspoons of sugar instead of 3, what happens? Try thinking of other experiments like these that you can try, and then try them!