时差N小时 致命的糖（在线收听）

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.

有些保存食物的方法很容易让人理解。例如将食物冷藏，或者用盐水腌渍，这两种常见的方法都能改变食物内部环境，使其不利于微生物生存，否则就会导致食物腐烂。你也许会觉得奇怪，然而果酱、果胶还有蜜饯均采用高浓度的糖来保存。糖分是维持基本生命活动最重要的因素之一，因此细菌和真菌也像我们一样需要糖。

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 literally 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.

在今日的科学时刻，我们会学习好的东西太多会如何造成致命的伤害，至少对微生物来说如此。糖可以使食物免于微生物的破坏，但是它还能引发口渴致死，毫不夸张！ 这是因为糖吸水性极好，溶液中糖分浓度越高，从周围环境中吸收的水分越多。

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 dehydrate. This process is called "osmosis," and it can be deadly for bacteria and mold.

这对寄生在罐装的果酱里的微生物来说可不是好消息。高浓度的糖会将细菌体内赖以生存的水分从细胞壁吸引出来，造成细菌脱水。这个过程就叫做“渗透作用”，它对细菌和霉菌有致命的威胁。

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 oasis in the desert, condensed water dripping from the jar's lid can give a dehydrating microbe the relief it needs.

为了让渗透作用发生，糖的浓度必须达到很高。如果你的果酱上落了一滴水，这一处糖的浓度可能就降低了，低到允许霉菌滋生的程度。这就是为何果酱、果冻和蜜饯一旦开封，就一定要放到冰箱冷藏的原因。如同沙漠中的绿洲一般，瓶盖上凝聚的水滴也能给微生物喘息的机会。