Why do raisins last longer than grapes?

Think about a cold, juicy grape. When you bite it, sweet juice bursts out and runs over your tongue. Now think about a raisin, small and wrinkly and chewy.

Leave a bowl of grapes on the table, and after about a week they turn soft and spotty. A box of raisins in the cupboard stays good for months. Why do raisins last longer than grapes?

Let's start with the grape. Inside its thin skin, a grape is almost all water, mixed with a little sugar. That water is what makes it plump and juicy.

All around us float microbes, which means living things far too small to see. They drift through the air and land on everything, even on the fruit in your kitchen.

Microbes need water to grow, just like you need a drink. A juicy grape gives them all the water they could want. The microbes on a grape grow and spread, and within a week they make it soft and spotty.

Now for the raisin. To make raisins, farmers lay ripe grapes out on trays in the hot sun. The warm sun pulls the water out of the grapes, and it slowly dries up into the air.

Over a few weeks, each grape loses most of its water. With so little water inside, its skin shrinks and folds into wrinkles, and the grape becomes a raisin. Now imagine a tiny microbe landing on that raisin. What do you think it finds there?

It finds almost no water to drink. Without water, the microbes on a raisin cannot grow and spread.

The raisin also keeps all the grape's sugar, packed tight inside. That sugar holds on to the last bit of water, so the microbes cannot get it. That is why a raisin stays good for months.

Microbes. Farmers dry grapes in the sun until almost no water is left, and the packed sugar holds on to the rest, so microbes have nothing to drink and cannot grow on a raisin.

Next time you pop a chewy raisin into your mouth, you will know the sunny secret that keeps it good for months.