Kitchen chemistry: The science of ice cream

Ice cream world record

Heston Blumenthal meets Peter Barham, a physicist who is mad about food. During the video, he attempts to break the world record for making the fastest litre of ice cream. Peter uses supercold liquid nitrogen with a temperature of -196 °C in an attempt to beat his previous record of 53.5 seconds. The ice cream is made from a simple mixture of sugar and cream. Recipes that contain egg would require heating, but there is no time for that during a world record attempt. The addition of liquid nitrogen causes ice crystals to form so fast there is no need to churn the ice cream as it freezes. At this low temperature, lactose crystallisation cannot take place and the resulting ice crystals are very fine, creating a really smooth dessert.

Making ice cream

Heston Blumenthal is a self-professed ice cream fanatic and as a result, he is quite particular about the way he thinks ice cream should be served. However, all ice cream consists of the same five things: ice crystals, fat, sugar, air and other solids. The secret to perfect ice cream is therefore in the method of making it.

According to Heston, ice cream should ‘melt in the mouth really easily and have no chewiness at all’. Heston describes three pitfalls to avoid if you want to make ice cream like his:

1. Lactose crystallisation: sugar molecules from the milk join together to make sandy lumps in your ice cream.
2. Overcooking the egg proteins: these will bunch together and the ice cream gets lumpy, just like scrambled egg.
3. Large ice crystals: if the crystals grow too large they’ll be bigger than the gaps between your teeth and the ice cream will feel gritty.

The flavour of ice cream

In this short video clip, Heston Blumenthal introduces ‘a great little variation on vanilla ice cream which embodies a really interesting piece of flavour chemistry’. He explains that fat holds flavour but in his recipe, the vanilla ice cream is made with milk, not cream, so its flavour ‘peaks higher but fades faster’. Heston adds jelly cubes of chocolate and pistachio which are full of fat so they release the flavour much more slowly. Heston describes this as a new invention: ‘vanilla with encapsulated chocolate and pistachio flavour release’.

Primary science teaching notes

If you teach primary science, see the headings below to find out how to use this resource.

Skill development

Learners will develop their working-scientifically skills by:

• Drawing conclusions and raising further questions that could be investigated, based on their data and observations.
• Using appropriate scientific language and ideas to explain, evaluate and communicate their findings.
• Using a range of scientific equipment to take accurate and precise measurements or readings.

Learning outcomes

Learners will:

• Compare and group materials together, according to whether they are solids, liquids, or gases.
• Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius.

Concepts supported

Learner will:

• Discover that materials can change state from liquid to solid, using the example of making ice cream.
• Learn that some stages of the making of ice cream are reversible and some are not.

Suggested activity use

This resource provides a hook into researching how ice cream is made, with learners having the opportunity to make their own, following a simple recipe involving milk, sugar and ice. Learners can observe the chemical process that happens as the ingredients become solid ice cream.

Practical considerations

You will need to find a simple recipe for making ice cream that the learners can follow, and provide the necessary ingredients and equipment.

Please take into account any health and safety considerations, especially as the temperature of the ice and salt mixture can become very cold. Children will need supervising.