What you'll need:
- Dried yeast (you can find this in supermarkets, in the baking section)
- Warm water
- Plastic drinks bottle (no bigger than 500ml)
- Funnel or a piece of paper
- Measuring tape or string and a ruler
The adult in charge is responsible for ensuring children don't use materials they are allergic to.
Pour some warm water into the plastic drinks bottle until it is around 3cm full.
Pour one packet of dried yeast into the drinks bottle, using a funnel or a rolled-up piece of paper to help. Gently swirl the bottle. The water activates the yeast.
Add one teaspoon of sugar into the drinks bottle, using the funnel. Gently swirl the bottle again to mix everything together. The sugar is a source of food for the yeast.
Fasten the neck of the balloon around the rim of the drinks bottle.
Leave the bottle in a warm place (e.g. by a radiator) for 20 minutes. The yeast can now carry out a chemical reaction that keeps it alive and allows it to grow. This reaction releases carbon dioxide gas, which causes the balloon to inflate.
After 20 minutes, use a measuring tape to measure all the way around the balloon at the widest part. If you don’t have a measuring tape, use a piece of string and measure this against a ruler.
Did you know?
Our Fermentation Lab produces over 10,000 litres of yeast and other microorganisms every year! The lab has 5 large containers, called fermenters, in which the yeast is grown.
A constant supply of yeast is important for our scientists, who use yeast to learn more about how cells work and then apply that knowledge to our own cells.
Here's an image of a yeast cell under a microscope:
Now that you know what yeast needs to survive, can you find out how to make the yeast grow as quickly as possible? Our scientists need lots of yeast for their experiments, so the faster it can be grown the better!
Here are some ideas to help:
- How much sugar is best? Try different amounts.
- What type of ‘food’ is best? You could try honey or syrup.
- What temperature is best? You could leave the bottle in different places.
- Maybe you can think of something else to investigate!
Download our worksheet if you’d like to record your results.
Make sure you empty the bottle not long after completing your experiment, otherwise it might go a bit gross!
When you do this, place the bottle in a sink and then carefully peel off the balloon to avoid mess.
It might not look like it, but yeast is alive! Like all living things - including us - yeast carries out a chemical reaction known as respiration. This reaction is essential to life – it releases energy from sugar, and that energy is then used for vital processes such as growth and repair.
Respiration happens in all living cells, and it's the reaction taking place in the bottle. When the dried yeast is added to water, the yeast cells activate and begin to function. Once the sugar is added, the yeast cells carry out respiration to release energy from the sugar. Carbon dioxide gas is released as a waste product during the reaction - this is why the balloon inflates.
There are over 1500 different kinds of yeast! The scientific name of the one you are using is Saccharomyces cerevisiae. This type of yeast has lots of important uses, from scientific research to baking!
Real life science at the Crick
Real life science at the Crick
Looking at the frothy mixture in your drinks bottle, you might not see much of a resemblance between yourself and yeast! Yet we have a lot more in common with yeast than you might think.
All living things are made up of cells, the building blocks of life. Yeast is a single-celled organism, whilst we are made up of trillions of cells! Despite the difference in numbers, the processes that take place in the cell of a yeast are very similar to what happens in our own cells. This similarity, combined with yeast being very easy to grow, means that yeast is a very useful model organism for learning more about our own biology.
One process in particular that our scientists are interested in is cell division. The purpose of cell division is to create more cells, for example for growth or repair. Sometimes mistakes can happen during this process, leading to diseases such as cancer. By using yeast to better understand cell division, our scientists can develop new ways of preventing and treating diseases.