時差N小時:致命的糖 Death by Sugar

Some methods of preserving food are easy tounderstand. For example, it's easy to see thatfreezing your food, or packing it in salt, would makeit inhospitable to the microbes which wouldotherwise cause it to spoil. You might wonder,however, about jams, jellies, and preserves, all ofwhich are protected from spoiling by a highconcentration of sugar. Sugar is one of the mostbasic foods for all life--bacteria and mold like to eatit just as much as we do.

有些保存食物的方法很容易讓人理解。例如將食物冷藏，或者用鹽水腌漬，這兩種常見的方法都能改變食物內(nèi)部環(huán)境，使其不利于微生物生存，否則就會導(dǎo)致食物腐爛。你也許會覺得奇怪，然而果醬、果膠還有蜜餞均采用高濃度的糖來保存。糖分是維持基本生命活動最重要的因素之一，因此細菌和真菌也像我們一樣需要糖。

On today's Moment of Science we'll learn how too much of a good thing can be deadly, at leastfor microorganisms. Sugar works not by poisoning the food-spoiling microbes, but by causingthem to literally die of thirst. This is because sugar attracts water very well; the more sugarthere is in any solution, the more water it tries to draw from its surroundings.

在今日的科學(xué)時刻，我們會學(xué)習(xí)好的東西太多會如何造成致命的傷害，至少對微生物來說如此。糖可以使食物免于微生物的破壞，但是它還能引發(fā)口渴致死，毫不夸張! 這是因為糖吸水性極好，溶液中糖分濃度越高，從周圍環(huán)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 concentrationsof 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.

這對寄生在罐裝的果醬里的微生物來說可不是好消息。高濃度的糖會將細菌體內(nèi)賴以生存的水分從細胞壁吸引出來，造成細菌脫水。這個過程就叫做“滲透作用”，它對細菌和霉菌有致命的威脅。

In order for osmosis to work, the sugar concentration has to be quite high. If any water fallsonto the surface of your jam, the sugar concentration at that spot might become low enoughto allow mold to grow. That's why it's important to take the back up measure of refrigeratingall 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 itneeds.

為了讓滲透作用發(fā)生，糖的濃度必須達到很高。如果你的果醬上落了一滴水，這一處糖的濃度可能就降低了，低到允許霉菌滋生的程度。這就是為何果醬、果凍和蜜餞一旦開封，就一定要放到冰箱冷藏的原因。如同沙漠中的綠洲一般，瓶蓋上凝聚的水滴也能給微生物喘息的機會。