This is the VOA Special English Development Report.

Before refrigerators, homes usually had ice boxes. But another way to keep food cool without the need for electricity is to use an evaporative cooler（蒸發冷卻器）. This is easy to make and does not even use ice.

A common design is a tall box with food placed on several shelves inside. The shelves are pieces of metal with many small holes through them. The sides of the box are covered with pieces of thick cloth.

Containers of water are placed at the top and bottom of the cooler. The ends of each piece of cloth lie in the water so the cloth stays wet.

Put the cooler in the open air but not in the sun. Air will pass through the wet cloth. The inside of the box will stay several degrees cooler than the outside air temperature. And this may be cool enough to keep foods fresh at least for a short time.

Cold storage in a freezer, however, can keep foods in good condition for months after the growing season. Yet foods can be damaged if they are kept too cold.

The British development group Practical Action says the best way to prepare foods for storage is at harvest time while still in the field. Use a sharp knife to avoid damage.

Place the harvested items on a clean surface or directly into storage containers. Do not put them on the ground.

Use clean water to remove dirt, and keep the water clean. Usually it is better not to remove outer leaves from fruits and vegetables before storage. Without the leaves, food can become dry.

Fruits and vegetables must be cool from field heat before they are put into storage. If they are placed in cool water, however, it can spread fungus throughout the food. A better idea is to harvest foods either early or late in the day, then leave them to cool naturally.

Some fruits and vegetables must be stored at zero to four degrees Celsius. Any colder, and they might be damaged. Others need four to eight degrees. And still others must be stored above eight degrees.

Wet the fruits and vegetables so they do not become too dry. The best time to do this is before storage. Cover the items in plastic once they reach the right "critical temperature" for storage. Most fruits and vegetables need the relative humidity in storage to be kept between eighty-five and ninety-five percent.

Finally, leave space between the food containers and the walls of the storage area so air can flow. Keep the space clean. And try not to open the doors too often.

And that's the VOA Special English Development Report.