英语听力文摘 English Digest 153、致命的糖

　　Some methods of preserving food are easy to understand.
For example, it's easy to see that freezing your food, or packing it in salt, would make it inhospitable to the microbes which would otherwise cause it to spoil. You might wonder, however, about jams, jellies, and preserves, all of which are protected from spoiling by a high concentration of sugar. Sugar is one of the most basic foods for all life--bacteria and mold like to eat it just as much as we do. On today's Moment of Science we'll learn how too much of a good thing can be deadly, at least for microorganisms.
Sugar works not by poisoning the food-spoiling microbes, but by causing them to literally¹ die of thirst.
This is because sugar attracts water very well; the more sugar there is in any solution, the more water it tries to draw from its surroundings. This is bad news for any microbe that happens to be inside a jar of jam. High concentrations of sugar will suck the microbe's vital water right through its cell wall, causing it to dehydrate². This process is called "osmosis," and it can be deadly for bacteria and mold.
In order for osmosis to work, the sugar concentration has to be quite high. If any water falls onto the surface of your jam, the sugar concentration at that spot might become low enough to allow mold to grow. That's why it's important to take the back up measure of refrigerating all jams, jellies, and preserves once you've opened them. Like an oasis³ in the desert, condensed water dripping from the jar's lid can give a dehydrating microbe the relief it needs.

1 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

2 dehydrate   

vt.使脱水

参考例句：

• People can very quickly dehydrate in the desert.人在沙漠里很快就会脱水。
• Without these structures, many warm-blooded animals would quickly dehydrate,especially in dry climates.没有这样的结构，许多温血动物将很快脱水，特别是在干燥的气候条件下。

3 oasis   

n.（沙漠中的）绿洲，宜人的地方

参考例句：

• They stopped for the night at an oasis.他们在沙漠中的绿洲停下来过夜。
• The town was an oasis of prosperity in a desert of poverty.该镇是贫穷荒漠中的一块繁荣的“绿洲”。