One option to consider coming into the summer months is to experiment with ice cream making as part of a food technology focus, which can be done simply and easily with minimal equipment.
Ice cream is an emulsion where fats, sugars and flavouring are combined together.
The smooth, creamy texture of ice cream comes from using techniques where the ice crystals which form are controlled so that they are small and plentiful, rather than large.
Large ice crystals tend to make an ice cream which is crunchy and can taste slightly watery, whereas small crystals make an ice cream which is smoother and more palatable.
It can be helpful to introduce students to the science of ice cream making by watching some short video clips of the process online, or doing some research at local ice creameries and looking at flavours, styles of ice cream and techniques used.
Some students may already have ice cream makers at home or may have seen one in action.
Ice cream makers typically rely on freezing a special double layered bowl for around 12 hours then adding the ingredients to the bowl and churning it for about 20 minutes before freezing the resulting ice cream for an additional few hours.
In the science room or classroom, ice cream can be made by combining ice cream ingredients (1/2 cup thickened cream, 3/4 cup full cream milk, 1/4 cup sugar and 1/4 teaspoon of vanilla essence) in a small zip lock bag and sealing it carefully.
The whole process can be completed in a 60 minutes class session, allowing enough time at the end for cleaning up and also eating the results!
The zip lock bag is placed inside a coffee or Milo tin with ice and around a quarter of a cup of rock salt packed around the bag and the lid sealed tightly.
The tin is then rolled or gently shaken for around ten minutes, with regular checks in between to see how the ice cream is progressing.
If necessary, more ice can be added to the tin before it is rolled or shaken again.
Eventually the liquid in the zip lock bag will turn to a solid which can be turned out into a bowl and eaten.
The trick to avoiding a slightly salty flavoured ice cream is to pat the bag dry with a tea towel first to remove any salty water from the outside, then open the bag.
So where’s the science?
The freezing point of water is usually thought of as simply ‘zero degrees’, but in fact this can be varied depending on factors such as pressure or chemical changes.
By adding the salt to the ice the freezing point is reduced, and this can be demonstrated to students by asking them to put a thermometer in the ice without salt and measuring the temperature and then adding rock salt and observing the change in temperature.
It is likely that the temperature will drop to around -14 degrees Celsius when the rock salt is added.
An endothermic reaction occurs so that the energy from the cream mixture is transferred to the ice and after a while it changes state to become lovely, sweet ice cream. It is important to remind students that the ice (and indeed the tin) will become extremely cold to touch once the salt is added.
Precautions such as rubber gloves or a towel can make it easier to handle the tin and avoid possible skin damage from the cold surfaces.
It may also be wise to wear safety goggles, particularly if you are working in the science room.
Check for any dairy allergies and consider allergies if you decide to add toppings to your ice cream.
Ensure students are well supervised and that all safety instructions are followed.