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Stroll through the frozen foods section of the supermarket and you’ll find frozen corn, peas, and beans. A Moment of Science wonders, why isn’t there any frozen lettuce?
你在閑逛超市的冷凍食品區的時候，會看到有冷凍玉米、冷凍豌豆和冷凍大豆。《科學一刻》欄目很好奇，為什么看不到冷凍萵苣呢？
Freezing is a relatively easy and convenient way to preserve many vegetables because it slows down or destroys the bacteria and enzymes that cause spoilage.
冷凍是儲藏很多蔬菜的一種相對簡單、便捷的方法，因為它會減慢導致食物變質的細菌和酶的增長或者殺死它們。
But, the freezing process itself can cause changes in food that can spoil the appetite.
但是，冷凍過程本身就會改變食物，從而影響食物的口感。
During freezing, the water in every cell of the vegetable freezes and forms ice crystals. As we know from our ice cube trays, water expands in volume when it is frozen.
在冷凍過程中，蔬菜的每個細胞中的水都會結冰。從制冰格我們可以知道，水在凍冰時體積會膨脹。
In frozen vegetables, the ice crystals expand and damage the wall that surrounds each cell.
對于冷凍蔬菜而言，冰晶膨脹會破壞蔬菜細胞的細胞壁
When the cell walls are damaged, the vegetable’s structure is weakened, and its texture becomes softer.
細胞壁受損時，蔬菜的結構就會變得不穩定，質地就會變軟。
Some vegetables, like corn and peas, have a lot of starch in them but very little water. So they maintain their structure in spite of the cell damage.
像玉米和豌豆這樣的蔬菜含有大量的淀粉但含水量卻不高，因此就算是細胞壁受損，它們的結構也不會發生改變。
But, other vegetables, like lettuce and cucumbers, have a lot of water in them and more delicate cell walls.
但是像萵苣和黃瓜這類蔬菜本身水分較多，且細胞壁也更脆弱。
The ice crystals damage these vegetables so badly that they really can’t be frozen without turning into mush.
所以冰晶會對這類蔬菜造成很嚴重的影響，所以在沒被搗碎的情況下最好不要將它們冷凍起來。
Ice crystals can reduce almost any vegetable to mush if poor freezing technique is used. Slow freezing creates larger ice crystals than fast freezing and causes more damage.
如果冷凍方法運用不當，冰晶幾乎可以把任何蔬菜都變得軟綿綿。慢冷凍所形成的冰晶要比快冷凍大，因而造成的損害也更多。
Repeated thawing and freezing also creates larger crystals and can turn fresh, crunchy vegetables into unappetizing, mushy goo.
反復的解凍和冷凍也會形成較大的冰晶，能夠把新鮮的蔬菜變得黏黏糊糊，讓人沒了胃口。
Oddly enough, good freezing technique means boiling the raw vegetables for twenty seconds before quickly cooling and then freezing.
說來也奇怪，良好的冷凍方法竟然要把生蔬菜先煮沸20秒，然后快速冷卻，最后再冷凍起來。
The brief boiling makes the cell walls slightly more elastic.
短暫的煮沸可以使細胞壁變得更加有彈性。
