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How to build an evaporative cooler. Also, how to prepare fruits and vegetables for cold storage.
This is the VOA Special English Development Report.
Before refrigerators were invented, the next best thing was an ice box. But another way to keep food fresh is to use an evaporative cooler. A common design is a tall box with several shelves inside to hold the food. 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.
The cooler is put outdoors, 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.
Some foods can make you sick if they are stored in conditions that are not cold enough to prevent the growth of harmful organisms. Freezing can keep some 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 and 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. But cooling them in water 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. Some foods need to be stored at four to eight degrees, and some need to be stored above eight degrees for best results.
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 cold 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. I'm Steve Ember.
Источник подкаста: http://www.voanews.com/.