KS2 Science: At what temperature does yeast grow best at?

Primary resources > KS2 Science > Experiments in controlled environments

Video summary

Presenters Harry and Frankie want to bake some bread. Before they start, they need to work out how to activate the yeast.

So, they test which temperature yeast grows best at by putting a mixture into a bottle and topping it off with a balloon. As yeast grows, it gives off carbon dioxide, which causes the balloon to inflate.

They set up a fair test, changing the temperature of water in three bottles, keeping the amount of yeast, sugar and water the same.

Then they measure the size of the balloon as it collects the carbon dioxide created by the yeast mixture.

This short film is from the BBC Teach series Experimental.

Teacher Notes

Before Watching

Show your learners a bread roll. Tear it in half – what do they notice? Can they see the bubbles? These are what give bread its soft structure. How do they think they got there? Your learners may mention various raising agents used in cooking – adding air, using steam, adding baking powder or using yeast.

In this investigation we ask the question at which temperature does yeast grow best? Ask your learners what they think yeast might need to activate it? Encourage them to talk about any baking they may have done at home.

After Watching

Revisit the results with your learners. Ask them what does yeast need to grow? Why do bakers need to check their yeast is alive before they use it in baking? Your learners will spot that yeast grows better in warm temperatures. However, make sure they know that if yeast is too warm (60°C) it will die and is no longer active. Ask them to think about why that might be?

Try the investigation for yourselves. You could also try different enquiries such as changing the amount of sugar, water or yeast to see if that affects how much carbon dioxide is produced.

Health & Safety Note - if you try this experiment, please note that children should not work with water over 45°C. To avoid this risk, teachers can prepare flasks of water before the lesson.

Ideas for further learning

Find out more about microorganisms with this Bitesize guide.

Research microorganisms and find out about those which are helpful in food production. And find out about those which are harmful to our health. How can we keep ourselves healthy?

Find out how the invention of the microscope helped scientists to identify a whole new world of tiny microorganisms. Try making your own magnifier with just a drop of water on a piece of plastic.

Key Scientific Ideas

This investigation is especially useful when teaching children about gases.

• Yeast - yeast is a microorganism. It is a type of fungus. Most breads are made using Yeast. When bread is made, the yeast becomes spread out in flour. Once activated, yeast begins feeding on the sugars in flour, and releases the carbon dioxide that makes bread rise. NB: Yeast grows better in warm temperatures, up to 60°C when it dies and is no longer active.

• Micro-organisms - micro-organisms are living organisms that are too small to be seen with the naked eye. They are found almost everywhere on Earth. There are three types of micro-organisms: viruses, fungi and bacteria.

• Gases - gases are a state of matter. Gas particles move about at high speeds, they have no fixed shape or volume. In this investigation we use balloons to capture the gas so they we can measure how much carbon dioxide has been made.

Developing Practical Enquiry Skills

• Fair test - fair test enquiries are an opportunity for children to explore cause and effect relationships in science. Children find the answers to their questions in fair test enquiries by changing one variable (independent variable), measuring one variable (dependent variable) and controlling all other variables. Fair tests involve working systematically and analysing data to identify how one variable affects another.

• Measuring temperatures - we use a thermometer to measure temperatures in Celsius (°C) When showing your learners how to use a thermometer, ask them to look at the scale. What increments is the scale rising in?

A thermometer is usually made up of a small, hollow glass tube. At the bottom of the tube is a bulb, which holds a liquid. When there is an increase in heat, the liquid inside the bulb expands, pushing up into the tube. A decrease in heat lets the liquid contract, moving down the tube. The place where the liquid stops on the scale is where you can take the reading of the temperature. Ensure you read the thermometer at eye level, keeping it in the water to take the reading._
Note: always use a thermometer suitable for use with primary aged children.

• Constructing a table - tables are an important tool for collecting and organising information. Tables are made of columns and rows. Usually, the change variable (independent variable) is recorded in the left-hand column. The right-hand column records the measurements or observations (dependent variable). Each column should be labelled, including the units of measurement as appropriate.

These short film clips support teachers with practical enquiry. They can be both used as a resource for learners to watch at home. Or as a stimulus to support learners to plan and conduct their own science investigations. They link to the UK Science curricula.

Materials

• Compare and group materials together, according to whether they are solids, liquids or gases.

Living Things

• To develop their understanding of micro-organisms as living things.

Science enquiry / Working scientifically skills

• Pupils should plan different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary.
• Pupils should take measurements, using a range of scientific equipment, with increasing accuracy and precision, taking repeat readings when appropriate.
• Pupils should record data using tables.

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