Kitchen Chemistry: Preserves and Preservatives

Why can some food last so long?

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jamPreserving food means making it last longer.

Food goes off when bacteria break it down, and to do that they generally need water and oxygen. So… remove the water and oxygen and you’ll preserve your food!

Drying out food is one way to remove the water – raisins last much longer than grapes because of this very process!

Salt can be used to draw water out of food – and bacteria can’t grow in salty water – or brine as it’s often called. Brine also keeps oxygen out, and that’s why it’s used to pickle things like onions and gherkins.

Tinned FoodFruit in preserves, like jam and marmalade, is boiled which kills the bacteria, and then mixed with lots of sugar which helps create a difficult environment for bacteria to grow.

In your kitchen cupboards, you’ll probably see lots of tins. These are another great a way to stop oxygen getting to the food – until you get the tin opener out!

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