Why Do Grapes Turn into Raisins?

Step 1 of 5

Spoiling needs water.

Bacteria and moulds are mostly water themselves and can only grow where there is water to take up. Remove it and they cannot do anything at all.

Step 2 of 5

Drying concentrates everything else.

The sugar, acid and flavour stay behind while the water leaves. A raisin is about four times sweeter than the grape it came from, without a grain of sugar added.

Step 3 of 5

Sugar itself is hostile.

Once concentrated, the sugar pulls water out of any microbe that lands on it. That is why jam and honey keep too — they are too sweet to live in.

Step 4 of 5

The skin has to be dealt with.

A grape skin is waxy and keeps water in, which is the opposite of what drying needs. Producers dip or crack the skins so the water can actually get out.

Step 5 of 5

It is one of the oldest ways of keeping food.

Sun-drying needs no equipment and no fuel, which is why it turns up everywhere that has a dry season — grapes, figs, tomatoes, fish and meat alike.

Grapes and raisins are seriously poisonous to dogs, for reasons that were only worked out recently.