Lemonade-Ed - Trouble with Yeast

Activity: Trouble with Yeast

Special Brew

Rosie Brown often told this story to her children.

The Investigation

Lauren was never quite sure what yeast was. She asked her friend Ryan, and they decided to find an explanation for why yeast makes beer fizz.

Ryan put some water, sugar and yeast in a bottle near the radiator. After a few hours it began to bubble.

Ryan's idea explaining why something happens is called a hypothesis.

Lauren was predicting what would happen if Ryan's hypothesis was right.

Testing the hypothesis

Ryan and Lauren put the bottle with the yeast mixture on top of the radiator. It bubbled and frothed out of the bottle.

'I was right!' said Ryan. 'Let's see what happens if we boil the mixture i a saucepan first and then put it in the bottle - it should bubble really fast and maybe explode like Great Uncle William's beer!'

They boiled the mixture and carefully placed it back in the bottle on top of the radiator. Much to their surprise, it stopped bubbling completely.

They needed to come up with a new hypothesis.

Questions:

What was Ryan's hypothesis?
What was Lauren's prediction?
What evidence supported Ryan's hypothesis?
What evidence surprised Lauren and Ryan?

Back in class

Later, Lauren found out that yeast is a tiny fungus made of cells that can only be seen under the microscope. Just like any other living thing, yeast cells release energy from their food by respiration.

Another hypothesis sprang to mind. It could be something to do with respiration.

Questions:

What new evidence did Lauren have?
What do you think her new hypothesis

Uncle William used to squeeze the juice of a lemon into his beer barrel. He said it made it fizz better.

Can you think of a hypothesis to explain why lemon juice has this effect?
Think of a way of testing your hypothesis.
Predict what will happen if your hypothesis is correct.

Discuss these questions with your partner. Write down your answers.

What do you think a scientist needs to prove that an explanation is right or wrong?
Do you think that one piece of evidence is enough to disprove a theory? Give a reason for your answer.
Explain the meanings of these words: hypothesis, prediction and evidence.
What do you think Lauren and Ryan should do next?
Can you think of any other hypotheses you have tested in science? How did you test them?
Were they right?

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