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什么是鲜奶油?!

所属:听力板块 来源:普特英语听力 阅读:3637 次 评论:0 条 [我要评论]  [+我要收藏]

小编摘要:它,点缀着冰激凌圣代,南瓜馅饼,姜饼和热巧。它,甜美的乳脂让人味蕾为之倾倒。它,让节食者只能对着体重计兴叹。你可曾想过为什么高脂奶油搅拌后会变得松软、轻柔?今天的科学一刻将会为你揭晓谜底。

 What Is Whipped Cream?



It adorns ice cream sundaes, pumpkin pie, gingerbread, and hot chocolate. Its sweet creaminess tantalizes taste buds and sends dieters running from the scale. Did you ever wonder why heavy cream whips into soft, light peaks? You can find out by listening today's moment of science!

When you whip heavy cream, air is forced into the liquid, and a stable mass of bubbles forms. Each bubble is a tiny pocket of air encircled by a thin film of water with proteins and other substances dissolved in it.

The protein molecules that are caught in the bubbles are pushed and pulled by different forces, so they lose their normal shape. Once they lose their normal shape, the protein molecules bond together into a thin film, which stabilizes the bubble walls.

The proteins that stabilize whipped cream are the same as milk proteins, so it would seem that milk would whip into soft shiny peaks as well. But you could whip a bowl of milk all day and never get anything more than a light froth that would disappear almost immediately.

The difference lies in whipping cream’s high fat content. Whipping cream is from thirty to forty percent fat, in contrast to the four percent fat found in whole milk.

The fat molecules in cream form a strong, stable network that keeps the bubble walls from collapsing. Small spheres of fat molecules gather together in the bubble walls, where surface forces break open the sphere. The exposed fat molecules stick to each other, and the network forms.

The fat molecules in milk act similarly, but there aren’t enough of them to stabilize the milk foam for more than a few seconds.

什么是鲜奶油?

它,点缀着冰激凌圣代,南瓜馅饼,姜饼和热巧。它,甜美的乳脂让人味蕾为之倾倒。它,让节食者只能对着体重计兴叹。你可曾想过为什么高脂奶油搅拌后会变得松软、轻柔?今天的科学一刻将会为你揭晓谜底。

当你搅拌奶油的时候,空气会被搅入液体中,大量结构稳定的泡沫会产生。每一个泡沫都像是充满了空气的小口袋,空气被一层水薄膜包裹,薄膜是由蛋白质和其他物质溶解在一起所形成的。

被泡沫所包裹的蛋白质分子被不同的力量牵引推拉,失去了其原本的形状。一旦形状发生改变,蛋白质分子就会结合在一起形成薄膜,使得泡沫的内壁更加稳定。

使得鲜奶油稳定下来的蛋白质与全脂牛奶中的蛋白质如出一辙,所以看起来似乎牛奶也能被搅拌成柔软轻盈的泡沫。但即便是你搅拌一碗牛奶一整天,也只能搅拌出一些转瞬即破的泡沫。

两者的不同之处在于鲜奶油的高脂肪含量。鲜奶油大概含有30%到40%的脂肪,同牛奶的4%相比,可见一斑。

奶油的脂肪分子形成了坚固而稳定的网状结构,能使泡沫壁不破碎。脂肪分子的一些小球体聚集在一起融入泡沫壁,其表面压力可以击破小球体。暴露在外面的脂肪分子互相结合,形成网状。

牛奶中的脂肪分子大同小异,但由于数量有限,所以不足以使奶泡稳固,只能存在几秒钟的时间。

标签:听力文摘
1
2012-04-19 21:34 编辑:pliny
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