The science of ice cream

20th June 2003 at 01:00
According to Professor Douglas Goff of Guelph University in Canada, ice cream can be used "to demonstrate heat transfer in physics, freezing-point depression phenomena, and emulsions and foams in chemistry, or pasteurisation and the food use of seaweeds in biology".

Seaweed is not usually listed as an ingredient on the standard supermarket tub - or is it? If sodium alginate appears as a "stabiliser", then your ice cream contains extract of brown kelp. And carrageenan is an extract of Irish moss or red algae, once harvested from the coast of Ireland, near the village of Carragheen. Stabilisers are used to make ice cream smoother.

Now consider freezing-point depression and heat transfer, both illustrated by making ice cream using a mix of salt and crushed ice. The chemistry is complex, but basically salt lowers the freezing point of water. When salt grains are spread on ice, melting begins at the point of contact. This produces water, which starts to dissolve and distribute the salt, melting the ice further. Heat is absorbed in the melting process (an endothermic reaction) and this must come from the surroundings - in this case your nicely cooling ice cream.

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