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Tests with yeast

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Tests with yeast

For thousands of years , People all over the world have yeast for brewing beer and baking bread. Yeast is a type of fungus that lives on the skins of many fruits. Just a spoonful of yeast contains millions of separate , single – celled (very simple) organisms. Each one works like a tiny chemical factorytaking in sugar , and giving out alcohol and carbon dioxide gas. While they feed , the yeast grow larger and then reproduce by splitting in half.

Yeast turns graps juice into alcoholic wine, and makes beer from mixtures of grain and water . When it is added to uncooked dough, yeast produces gas bubbles that make the bread light and soft. Brewing gas bubbles that make tht bread light and soft. Brewing and baking are important mordern industries that depend on yeast working quickly.

This project consists of four separtae experiments. By comparing the results, you can discover the best condition for yeast to grow. It needs a moist environment to be active. Lack of moisture makes the cells dry out and hibernate (sleep). Add water to dried, powdered yeast, and- even after many years – it will become active again.

Finding the best conditions

You will need:

Measuring cup, water, kettle, adhesive colored labels, four small glass jars, teaspoon, dried yeast granules, sugar, scissors, plastic, wrap, three rubber bands, two heatproof bowls, ice cubes.

Finding the best conditions

test with yeast step01

1. Half fill a kettle with water. Ask an adult to boil it for you, and thwn put it aside to cool. Boiling the water kills all living organisms that might stop the yeast from growing.
test with yeast step02

2. Lable the glass jars, one to four. Put a level teaspoonful of dried yeast into each jar as shown of sugar into each jar.
test with yeast step03

3. Pour 2/3 cup of the cooled, boilws water into the first three jars. Stir the mixtureto dissolve the sugar. Do not pour water into the fourth jar. Put this jar away in a warm place.
test with yeast step04

4. Cut out pieces of plastic wrap about twice a jar’s width. Stretch one across the neck of each remaining jar, and secure it with a rubber band. Put the first jar in a warm place.
test with yeast step05

5. Place the scond jar in a glass bowl. This will keep the jar’s temperature close to freezing.
test with yeast step06

6. Place the third jar in another glass bowl. Pour in some hot water that is almost too hot to touch. Be careful not to use boiling water, or the jar may crack.
test with yeast step07

7. Regularly check all four jars over the next two hours. As the ice around the second jar melts, add more to keep the temparature low. Add more hot water to keep the third jat hot.
test with yeast step08

In the jar that was kept hot, the yeast is a cloudy layer at the bottom , killed by the heat . The jat that was kept cold has only a little on the surface, because the cold has slowed down the yeast.

The yeast that was kept warm has fed on the water and sugar , and its gas is pusing up the plastic wrap. In the dry jar there are no signs of activity, because the yeast is hibernating.


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