Food Preserving:Dehydrating

Did You Know? Raisins are dried out grapes.

Another way of describing raisins is that they are dehydrated grapes.

Dehydration is the process by which water is lost by something, such as grapes.

Even before the Native Americans hung strips of buffalo meat in the sun and wind to dry, people dried meats and other foods. They didn’t know they were producing an unacceptably dry environment for microbes, but they did know it kept their food from spoiling. Dehydration (process of removing water from) of food makes it last longer. Drying is one method of preserving food.

Raisins are made by dehydrating grapes. Before dehydration, the grapes are round and puffy. Like all plants, grapes are made up of cells with stiff cell walls. When water is removed from the grape cells, the cell walls are generally not changed, but the cells collapse without the water to fill them.

The process of one substance taking in another, such as a sponge soaking up water, is called absorption. Can raisins be  rehydrated (to return to a hydrated state)?

Discover for Yourself

1. Observe the appearance of raisins. Note their shape, and size.

2. Using clear plastic transparent cups, place 10 raisins in each.

3. Fill one of the cups about three-fourths full with water.

4. Allow the glasses to sit undisturbed overnight. During this time, observe the raisins in each glass as often as possible. Note any change in the shape, and/or size of the raisins.

Results

All the raisins look small and wrinkled at the start of the experiment. The appearance of the raisins in the glass without water does not change. But, the raisins covered with water increase in size and their shape is more rounded.

So, What Happened?

When raisins are placed in water, the cells fill with water and resume their original shape. Reconstitution is the process of rehydrating (to restore water) dried food, which mean the food is returned to its original hydrated (having water) form.

Science Challenge: I wonder…Would the hydrated grapes dehydrate if removed from the water and placed in an empty cup?

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