The science of milk - Jonathan J. O'Sullivan

翻译人员: Di SUN 校对人员: Jenny Yang

Why do humans drink so much milk?

为什么人类喝那么多奶？

And given that all mammals lactate,

所有哺乳动物都会泌乳，

why do we favor certain types of milk over others?

但我们为什么喜欢某些奶 胜过其他种类？

Milk is the first thing we drink,

母乳是我们最先喝到的东西。

and thanks to developments in the production and variety of dairy products,

多亏了制造业的发展， 乳制品不断多样化，

it can take on countless forms for our dietary and sensory well-being.

乳制品可以呈现数不尽的形式 有益于我们的饮食及感官。

Milk's primary function is as a complete source of nutrition for newborns.

奶水最主要功能是 为新生儿提供全面的营养。

In fact, since it has all of the vital nutrients for development and growth,

实际上，奶含有生长发育所需 所有的重要营养，

proteins,

包括蛋白质、

carbohydrates,

碳水化合物、

fats,

脂肪、

vitamins and minerals,

维他命和矿物质，

and water,

以及水分。

milk is the only thing a baby even needs to ingest

奶水是新生儿6个月大之前

for the first six months of life.

唯一需要摄入的。

The unique makeup of milk can vary depending on factors like species,

奶水的成分取决于许多因素， 比如物种、

diet,

饮食习惯，

and location.

以及地理位置。

Reindeer of the Arctic Circle, for example,

比如，北极圈的驯鹿

make energy-dense milk that's about 20% fat,

拥有能量密集型的奶水， 含有20%的脂肪，

roughly five times more than human or cow's milk,

大概是母乳或牛奶的5倍多。

to help their young survive the harsh, freezing climate.

这些成分能够保证 小驯鹿在严寒中生存。

So how is milk made?

那么，奶水是如何形成的呢？

In the uniquely mammalian process of lactation,

在哺乳动物特有的泌乳过程中，

a special class of milk-secreting cells known as mammocytes

有一类泌乳细胞叫做乳腺细胞。

line up in a single layer around pear-shaped alveoli.

它们沿着梨型肺泡 排成单层的一排。

Those cells absorb all of the building blocks of milk,

这些细胞吸收所有 用于制乳的成分，

then synthesize tiny droplets of fat

然后形成小的脂肪滴，

on structures called smooth endoplasmic reticula.

依附在平滑的内质网上。

The droplets combine with each other and other molecules

脂肪滴与脂肪滴 以及其他分子结合，

and are then expelled and stored in spaces between cells.

然后排出并贮藏于细胞之间的间隙。

Mammary glands eventually secrete the milk through the breasts, udders,

乳腺最终分泌乳汁， 通过乳房、乳头，

or, in the rare case of the platypus, through ducts in the abdomen.

或是像鸭嘴兽这中罕见地 通过腹部的导管。

Although this process is typically reserved for females,

泌乳通常被视为是 雌性动物的行为，

in some species, like dayak fruit bats,

一些物种，比如棕榈果蝠、

goats,

山羊，

and even cats,

甚至是猫，

males can also lactate.

雄性动物也能泌乳。

Milk drinkers worldwide consume dairy from buffalo,

世界各地的乳制品消费者 享用的乳品来自于水牛、

goats,

山羊、

sheeps,

绵羊、

camels,

骆驼、

yaks,

horses,

牦牛、

马，

and cows.

和牛。

Almost all of these species are ruminants,

这些大多是反刍动物，

a type of mammal with four-chambered stomachs

这种哺乳动物有4个胃室，

that yield large quantities of milk.

能够形成大量乳汁。

Of these, cows were the most easily domesticated

这些动物中， 奶牛是最容易被驯化的，

and produce a milk that is both easily separated into cream and liquid

其乳汁也很容易分成乳脂和液体两部分，

and has a similar fat content to human milk.

与人类母乳的脂肪含量相似。

In their natural environment,

在自然环境中，

mammals secrete milk on call for immediate consumption by their young.

哺乳动物分泌乳汁 随时供他们的幼崽食用。

But with the demands of thirsty consumers,

但面对饥渴的消费者，

the dairy industry has enlisted methods to step up production,

乳品业也提升生产速度，

enhance shelf life,

延长产品保质期，

and provide a variety of milk products.

同时提供多样的乳制品。

In the dairy, centrifugation machines spin milk at high speeds,

在乳制品生产厂， 离心机高速旋转牛奶，

forcing less dense fats to separate from the liquid and float up.

使密度较低的脂肪成分与 其他液体分离而上浮。

After being skimmed off,

脱脂后，

this fat, known as butterfat, can be used in dairy products

这部分脂肪，也被称为乳脂， 可以被用来制成其他产品，

like butter,

比如黄油、

cream,

奶油，

and cheese.

和芝士。

Or it can be later added back to the liquid in varying proportions

乳脂也可以按照不同比例 加回到乳液中，

to yield different fat content milks.

从而形成脂肪含量不同的牛奶。

Full fat milk, sometimes referred to as whole milk, has 3.25% butterfat added

全脂牛奶，也被称为全脂奶， 含有3.25%的乳脂。

compared to 1-2% for low and reduced fat milk,

相较而言， 低脂和减脂牛奶则含1-2%，

and less than half a percent for skim milk.

脱脂奶含有低于0.5%的乳脂。

To stop reseparation of the fat from the water, or creaming,

为防止乳脂和水分再次分离， 形成乳状分离物，

the mixture undergoes the high-energy pressurized process of homogenization.

混合物会经历一个高能量加压的 均质化过程。

Before milk hits the shelves, it's also typically heat treated

在被摆上货架之前， 牛奶还经过了热加工，

to reduce its level of microbes,

以减少微生物数量。

a government-sanctioned process

这一过程经过政府批准的，

that raw milk enthusiasts argue may reduce milk's nutritional worth.

而生乳爱好者则认为 这会降低乳品的营养成分。

Milk spoilage is started by microbes,

奶的变质源于微生物，

which consume and break down the nutrients in milk.

消耗并分解奶中的营养成分。

That process causes butterfat to clump together,

这一过程中， 乳脂凝结成块，

leading to a visually unpleasant product.

形成很不好看的东西。

And the byproducts of the microbes' consumption

微生物消耗形成的副产品

are compounds that taste and smell nasty.

则是味道和气味恶心的化合物。

But there's a bigger problem.

这里还有一个更大的问题。

Raw milk can carry microbes that are the sources of deadly diseases,

生乳中可能有携带致命疾病的微生物。

so in order to kill as many of those microbes as possible,

为了杀死尽可能多的微生物，

and keep milk fresh longer,

同时延长奶的保鲜期，

we use a technique called pasteurization.

我们采用巴氏灭菌法。

One version of this process involves exposing milk

其中一种方式是把牛奶

to about 30 seconds of high heat.

在高温下加热30秒。

Another version, called ultra-high temperature processing,

另一种方式， 被称为极端高温处理（UHT），

or ultra pasteurization,

或是超高温灭菌法，

blasts the milk with considerably higher temperatures over just a few seconds.

是让牛奶在超高温下加热几秒。

UHT milk boasts a much longer shelf life,

极端高温处理的牛奶 拥有更长的保质期，

up to twelve months unrefrigerated,

不放冰箱可以保存12个月。

compared to pasteurized milk's two weeks in the fridge.

而普通的巴氏灭菌奶 只能在冰箱保存2周。

That's because the higher temperatures of UHT processing

这是因为超高温处理过程

inactivate far more microbes.

使更多微生物失去活性。

Yet the higher processing temperatures

但是高温处理

may adversely affect the nutritional and sensory properties of the milk.

可能造成营养成分流失 以及口感改变。

Ultimately, that choice lies in the consumer's taste

最终，这种选择在于消费者

and need for convenience.

对于口味和便利程度的偏好。

Fortunately, there are many choices available

所幸的是，

乳品业每年生产超过8.4亿吨产品， 我们有很多的选择。

in an industry that produces in excess of 840 million tons of products each year.