英语听力文摘558 为怎样防止面包变质？

Generally speaking, refrigeration helps to keep food fresh. Fruits, vegetables, and dairy products all last longer if kept cool.

But don’t try to store a loaf of bread in the refrigerator if you want it to stay fresh–refrigeration is the quickest way to make bread go stale.

Stale bread，on this moment of science.

As bread ages, it develops the dry, crumbly texture and leathery crust that define staleness. But staling isn’t simply a matter of the bread drying out. Bread can grow stale even if it’s sealed tightly enough that no water can escape from the loaf.

Bread stales when the starch inside the loaf loses its ability to hold water. Chemical changes in the starch inside the loaf cause it to lose water. The water moves to the starch in the crust, which begins much drier than the rest of the loaf.

Of course, if the bread is left uncovered, the water escapes to the air.

Staling depends largely on the temperature the bread is stored at, since temperature affects the ability of the starch in the bread to hold water. The drop in water-holding capacity is slowest at temperatures below freezing, so frozen bread stales very slowly.

The starch’s water-holding capacity decreases more quickly at room temperatures, and most quickly at refrigerator temperatures, which are just above freezing. In one experiment, refrigerated bread staled as much in one day as bread stored at room temperature staled in six.