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What is milk?

2011, Nature, http://blogs.nature.com/soapbox_science/2011/03/09/what-is-milk

Peter Atkins, Durham University

What is milk may sound like a trivial question or an inappropriate one for a serious science blog.

Why should we take any interest at al l in a substance that is a matter of everyday consumption? Put

on the spot, most people would say that milk is a rather dull commodity and something they take for

granted. The Spanish have a saying: blanco y en botella, leche. Literally this is if its white and

in a bottle then its milk but slipped colloquially into conversation it means its obvious.

My purpose in this post is to show that a discussion of milk is far from obvious and indeed is

something that cannot be left to dairy science alone. We need to look beyond that to

understand why milk is as it is today and, ultimately, what is at stake is the quality of all of

the food that we consume.

The laboratory-based analysis of milk has its origins in the late eighteenth century. In the

1790s Parmentier and Deyeux were already estimating its constituents with simple

experiments and they were followed in the early nineteenth century by other French,

Swedish and German scientists. But milk, as a complex emulsion of fat globules and water,

and a fine dispersion or suspension of casein micelles, was very difficult to know given the

still emerging techniques of organic chemistry and physics. It was eventually realised that

milk is a highly variable substance according to mammal species and factors such as feed. Its

principal constituents, fat, protein and sugar, also vary from one breed of dairy cow to

another.

So what you might ask. Well, food in the nineteenth century was frequently adulterated,

and milk was the most notorious example because its dense whiteness enabled the addition

of small amounts of water without anyone noticing. The average pint in London in the

1870s, for instance, contained about 25% of added water. Consumers were outraged by the

unreliable quality of one of the most important of foods but there was a feeling of

helplessness because it was shown that a precise science of milk composition continued to

be elusive into the last decades of the century. One simple method of analysis used by the

milk trade was the lactometer, which measured the specific gravity of milk, but this had to be abandoned when it was realised that, by adding water and removing some of the

butterfat, it was possible to simulate the physical properties of genuine milk.

Gravimetric and volumetric chemistry eventually made progress and adulterators were

brought to book under a series of Sale of Food and Drugs Acts that started in 1860. The

irony was that many innocent farmers were prosecuted before anyone thought to establish

a legal definition of the real thing. This came in 1901 with the Sale of Milk Regulations,

which in effect claimed that science could determine natures intentions. Natural cow milk

was said to contain 3.0% of butterfat, for instance, and a milk that was more watery than

this was presumed to have been fraudulently manipulated.

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Problem solved? Well no, because what happened if cattle were fed on very watery grass or

silage? The milk they produced would be as it came from the cow, nothing added and

nothing taken away but it would still be of a low quality fat-wise. Legal challenges in the

early twentieth century proved that almost any milk coming from a healthy cow was

acceptable, as long as it was not modified later. Here science and the law combined and feltable to say definitively what was natural.

From 1901 to 1976 this whole milk idea remained the British consensus. Meanwhile on the

Continent a completely different approach prevailed. Countries such as the Netherlands had

butter industries, where it was in their economic interest to regard some extraction of fat as

normal. This led at first to fixed legal limits of quality and later to the standardization of the

constituents of milk. Britains entry into the European Community in the 1970s meant

accepting some legal definitions of foods that were from the Continental tradition. As a

result, it was possible for the first time to buy semi -skimmed milk from 1981 onwards, andmilks with standardized composition had to be allowed with the beginning of the Single

Market in 1993. But it has only been since the Drinking Milk Regulations of 2008 that, at

last, milk could be labelled with various fat levels.

When you next go to the supermarket, have a look at the dairy shelves. Youll find there an

astonishing range of milk. In addition to flavoured or filtered or fortified milk, you will find

milk with 0.1%, 1%, 2% and 4% fat, and the consumer in England and Wales (but not

Scotland) can also choose between raw milk and heated treated milks that have been

pasteurized, sterilized or ultra heat treated. There is also homogenized and organic co ws

milk, not to mention goats milk and soya milk.

Im not saying that these new Euro definitions of quality are better or worse, but they are

certainly different from the long history of milk in Britain. It is almost as if milk has had its

own life story and we can now write its biography. It seems that most milk drinkers are

oblivious to this story and are now content that it is technology that defines what is genuine

and natural, and we no longer feel any obligation for our diet to reflect the foibles and the

cycles of nature. We are now sure that we can improve upon nature by producing a

substance which has a substantial human imprint. Milk still resists us by turning sour and by

persisting in being an ideal medium for the spread of disease, but both of these problems

are susceptible to industrial processing.

Finally, I would point out that science meets food quality in another interesting way, and

once again attitudes have differed on either side of the Channel. In Britain regional foods

were annihilated or marginalized by cheap imports from around the world in the second

half of the nineteenth century. But free trade in other European countries was carefully

managed in order to prevent the destruction of domestic agriculture. As a result, food

quality in countries such as France and Italy has tended to be associated more with place

than with the British-style chemical vision. These place-based interpretations of food qualitywere enshrined in European law in the 1990s and since then it has been fascinating to see

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British food culture retro-fitting the notion of locality, without any appreciation that the

appeal ofterroir was often a defensive measure by French wine producers hoping to

protect their reputations and their trade in the early twentieth century.

Dont get me wrong, I love French and Italian food and wine but it is important to see

beneath our romantic vision of them at the hard-headed business sense that has been the

basis of the genealogy of their quality. Just because one vision has become so persuasive

that it is now hegemonic does not mean that we should shirk our duty to trace its roots.