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Some methods of preserving food are easy to understand. 

一些保存食物的方法很容易理解。

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.

比如，把食物冷藏，或者用盐腌起来，都是很常见的方法。通过这些方法，不给细菌提供滋生的环境，以防止食物腐败变质。

You might wonder, however, about jams, jellies, and preserves, all of which are protected from spoiling by a high concentration of sugar.

不过，果酱，果冻和蜜饯都是用高浓度的糖来防止其变质的，你可能对此感到疑惑。

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.

糖是生物的最基本食物之一-如我们一样，细菌和真菌也喜欢糖。在今天的《科学时刻》节目中，我们来见识见识，什么叫物极必反：太多的糖也会致命-至少对微生物来说是如此。

Sugar works not by poisoning the food-spoiling microbes, but by causing them to literally¹ die of thirst.

糖之所以能杀灭会令食物变质的细菌，并不是因为它有毒，而是高浓度的糖让细菌“渴死”了。

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.

这是因为，糖的吸水性较好，在任何溶液中，糖的含量越高，其越能从周围吸水。这对恰巧滋生在一瓶果酱里的细菌来说可不是什么好消息。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。这一过程被称为“渗透作用”。对细菌和霉菌来说，这可能是致命的。

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.

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，那一点的糖的浓度可能就降低了，到了霉菌可以滋生的程度。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。

Like an oasis³ in the desert, condensed water dripping from the jar's lid can give a dehydrating microbe the relief it needs.

如同沙漠中的绿洲一般，凝结的水滴从瓶盖上落下，便给正处脱水状态的细菌必要的喘息时机。