英国学生科学读本 第91期:牛奶及用途(2)（在线收听） |
Soon all the little balls of cream have their skins or coats broken, and then the tiny pieces of milk-fat inside them stick together and make a lump of yellow butter. 很快, 奶油小球的外膜破碎, 里面的乳脂颗粒则会黏在一起成为一块黄油。 You can make a little butter for yourself by putting a few spoonfuls of cream into a bottle, 你也可以自己制作黄油：将几勺奶油倒入瓶中,
and shaking it as hard as you can for a while; but you will likely feel very tired before the butter appears. 然后竭尽全力地摇晃一阵瓶子；不过, 在黄油成型之前, 你一定会累得不行。
The "skim-milk" which remains after the cream has been taken away is of a bluish-white colour; 不包含奶油的“脱脂牛奶”是一种青白色物质；
and while new milk sells for, perhaps, threepence per quart, skim-milk fetches only a penny. 如果鲜牛奶的价格是每夸脱三便士, 那么脱脂牛奶就只能卖到一便士。
Yet there is good nourishment in skim-milk. 然而, 脱脂牛奶的营养价值同样很高。
Let us add a little acid—vinegar will do—to some skim-milk. 现在, 我们往脱脂牛奶中加一些酸性物质, 比如醋。
This makes it curdle , and we see little white jelly-like clots or "curds" forming. 这样的话, 牛奶就会凝固, 我们能够看到逐渐形成的胶状凝块或者“凝乳”。
We will strain off the curds by squeezing the curdled milk through a piece of muslin. 我们用一块棉布将凝固的牛奶包裹起来, 用力挤压, 过滤掉凝块。
The white and solid curds that remain only need pressing to turn them into "cheese. " 剩下这些白色的固体凝乳经过压制便可成为“奶酪”。
The watery liquid that runs through the muslin is called "whey. " 通过棉布流出的水质液体就是“乳清”。
Dissolved in the whey there is a little milk-sugar, the substance that makes new milk taste sweet, and also some lime. 而溶解在乳清中的物质就包括少量的乳糖以及石灰乳, 正是前者的存在才使得鲜牛奶有些甜味。
Now we know why new milk is such an excellent food. 现在我们就知道了, 鲜牛奶果然是一种营养丰富的食物。
The milk-fat and the milk-sugar which it contains warm our bodies and help us to do our work, 乳脂与乳糖能够给人体带来热量并且提供我们开展各类活动所需的能量；
the curd helps to form our flesh, and the lime helps to form our bones. 凝乳有助于人体的肌肉生长, 而石灰乳则可以促进骨骼发育。
You can now see how good it is for us to drink milk, and why we add milk to many other kinds of food, such as tea, coffee, and cocoa. 如此一来, 你应该就可以明白饮用牛奶能够带来的好处以及我们要在茶、咖啡与可可中添加牛奶的原因了。
Have you ever seen condensed milk ? 你见到过炼乳吗?
This kind of milk is made by boiling fresh milk for some time, so as to evaporate part of the water contained in it, and then adding some sugar. 它的做法就是：将鲜牛奶煮沸并保持其沸腾状态, 从而将牛奶中的一些水分蒸发出去, 然后加入糖。
The sweet, thick liquid thus made is then put into tins, which are carefully closed and sealed, so as to keep out the air. 随后, 人们把这种甜蜜、浓稠的液体放入罐子中, 小心地盖好并密封起来, 这样就能够阻隔空气。
If kept in those air-tight tins, condensed milk will remain good for years. 如果保存在密封性能较好的罐子中, 即便经过了好几年, 炼乳依旧能完美如初。 |
| 原文地址：http://www.tingroom.com/lesson/syysdw/mgxskxdb/447733.html |