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Popcorn, like all grains, contains water. About thirteen and a half to fourteen percent of each kernel is made up of water. So when a popcorn kernel is heated above the boiling point of 212 degrees Fahrenheit, this water turns to steam. This steam creates pressure within the kernel, causing the kernel to explode and turn itself inside out. But, if the water inside a piece of popcorn is what makes it pop, why don't other grains pop as well?
与其他谷物一样，爆米花也含有水分。每粒玉米仁大约13.5%至14%的成分是水。因此当爆米花玉米仁被加热到超过沸点华氏212度时，水分会蒸发成水蒸气。水蒸气在玉米仁内产生气压，导致玉米仁外翻发生爆炸。如果玉米仁因为含有水分才能爆开，那为什么其他的谷粒不会爆开呢？
Wheat and rice contain water, so why don't we sit down to watch a movie with a bucket of popped 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, steam easily passes through, so no significant pressure is produced.
小麦和大米内也含有水分，那么我们为什么不手拿一包爆稻谷花或是爆小麦花坐下来观看电影呢？答案就在于爆米花跟其他谷物的外表（被称做外壳）不同。与大米、小麦不同，与一般的玉米也不同的是，爆米花的外壳没有可以渗透蒸气的小孔。其他谷物的外壳多孔，水蒸气能穿透这层外壳，因此不能形成显著的压力。
These grains may parch, but they will not pop. But even popcorn, with its special hull, doesn't always pop. Popcorn must have two important properties to pop well. First, the amount of moisture in the kernel must be very close to thirteen and a half percent. Too little moisture and enough steam won't build up to pop the kernel. Too much moisture and the kernels pop into dense spheres, rather than the light fluffy stuff popcorn fanciers love. Second, the kernels must not be cracked or damaged in any way. Even a small crack will let steam escape, keeping the necessary pressure from building. Popcorn kernels with the right amount of moisture and unblemished hulls pop into the snack that just about everyone enjoys.
这类谷物只能被烤干，而不可能爆开。然而即使是有着特殊外壳的爆米花，也不总是能爆开。爆米花只有具备两个条件才能很好得爆开。首先，玉米仁内水蒸气的含量必须非常接近13.5%。太干燥和太潮湿都不会使玉米仁发生爆炸。太多的水分会使玉米仁爆破成实心的球体，而不是爆米花爱好者所钟爱的蓬松状。第二，玉米仁不能有半点损伤或裂痕。即使是一丁点儿裂缝都会让水蒸气泄露，从而无法形成爆炸所需的压力。总之，拥有合适湿度和完好外壳的玉米仁就能够爆成大众喜爱的小吃——爆米花。
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