Emulsions. Fats. Ice crystals. And ice cream holds its ingredients together
Two very components in ice cream are fats (e.g. from the cream used) and the ice crystals that form when the ice cream is frozen. How smooth our ice cream is depends largely on the amount of fat in it and the size of the ice crystals.
Fat creates a creamier texture and the amount of fat can range from 10% up to about 20%. Ice crystals gives body but big crystals create a grainy texture. Small crystals are thus preferred (find out one way to keep the crystals small in this 1-Minute NomNom “Freeze!“).
But wait… how do ice crystals and fats come and stay together? After all, water and oil don’t mix i.e immiscible because oil does not like water (property known as being hydrophobic), so why should ice crystals and fats?
The secret lies in creating an emulsion where two immiscible liquids are dispersed in each other. And the secret ingredient is an emulsifier (compound or substance which prevents liquids from separating). In many cases, egg yolk does the trick.
The lecithin molecule in the egg yolk has one end likes water and another end that likes fats. It thus forms chemical bonds with both the ice crystals and fats, holding together permanently in an emulsion.
Egg yolks are just one type of emulsifiers. Others could include…
“… some diary products, seaweed extracts (such as carrageenan), lecithin, xanthan gum, cellulose gum, and various types of glycerides.” (Source: Lucky Peach)
The use of emulsifiers to create an emulsion is fairly common in food and science in general. For example, mayonnaise and Hollandaise sauces are both emulsions, formed – again – by egg yolks as emulsifiers.
And soap is an emulsifier that creates an emulsion of water and grease to that makes it possible to clean dishes, clothes and our bodies! You can read all about them in the 1-Minute NomNoms “Feeling negative? Mayo control your emulsions“, “Cooking gold“, and “Soap opera“.
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