時差N小時:爆米花為什么會爆?

Popcorn, like all grains, contains water. Aboutthirteen and a half to fourteen percent of eachkernel is made up of water. So when a popcornkernel is heated above the boiling point of 212degrees Fahrenheit, this water turns to steam. Thissteam creates pressure within the kernel, causingthe kernel to explode and turn itself inside out.But, if the water inside a piece of popcorn is whatmakes it pop, why don't other grains pop as well?

與其他谷物一樣，爆米花也含有水分。每粒玉米仁大約13.5%至14%的成分是水。因此當爆米花玉米仁被加熱到超過沸點華氏212度時，水分會蒸發(fā)成水蒸氣。水蒸氣在玉米仁內(nèi)產(chǎn)生氣壓，導致玉米仁外翻發(fā)生爆炸。如果玉米仁因為含有水分才能爆開，那為什么其他的谷粒不會爆開呢?

Wheat and rice contain water, so why don't we sit down to watch a movie with a bucket ofpopped rice or popped wheat? The answer lies in the differences between the outer coverings,called hulls, of popcorn and other grains. Unlike rice and wheat, and unlike even regular corn,popcorn has a non-porous hull that traps steam. With the porous hulls of other grains, steameasily passes through, so no significant pressure is produced.

小麥和大米內(nèi)也含有水分，那么我們?yōu)槭裁床皇帜靡话竟然ɑ蚴潜←溁ㄗ聛碛^看電影呢?答案就在于爆米花跟其他谷物的外表(被稱做外殼)不同。與大米、小麥不同，與一般的玉米也不同的是，爆米花的外殼沒有可以滲透蒸氣的小孔。其他谷物的外殼多孔，水蒸氣能穿透這層外殼，因此不能形成顯著的壓力。

These grains may parch, but they will not pop. But even popcorn, with its special hull, doesn'talways pop. Popcorn must have two important properties to pop well. First, the amount ofmoisture in the kernel must be very close to thirteen and a half percent. Too little moistureand enough steam won't build up to pop the kernel. Too much moisture and the kernels popinto dense spheres, rather than the light fluffy stuff popcorn fanciers love. Second, the kernelsmust not be cracked or damaged in any way. Even a small crack will let steam escape, keepingthe necessary pressure from building. Popcorn kernels with the right amount of moisture andunblemished hulls pop into the snack that just about everyone enjoys.

這類谷物只能被烤干，而不可能爆開。然而即使是有著特殊外殼的爆米花，也不總是能爆開。爆米花只有具備兩個條件才能很好得爆開。首先，玉米仁內(nèi)水蒸氣的含量必須非常接近13.5%。太干燥和太潮濕都不會使玉米仁發(fā)生爆炸。太多的水分會使玉米仁爆破成實心的球體，而不是爆米花愛好者所鐘愛的蓬松狀。第二，玉米仁不能有半點損傷或裂痕。即使是一丁點兒裂縫都會讓水蒸氣泄露，從而無法形成爆炸所需的壓力。總之，擁有合適濕度和完好外殼的玉米仁就能夠爆成大眾喜愛的小吃——爆米花。