Milk

• 1. Introduction

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  Milk is usually a white liquid, though it can shade into yellow, cream, pink, or brown. The mammary glands of lactating mammals produce it. For young mammals it is the primary source of nutrition before they can digest solid food. More than six billion people worldwide drink milk and eat milk products. Between 750 and 900 million people live in dairy-farming households. The first milk a newborn receives is called colostrum, carrying antibodies that strengthen the immune system against many diseases. Yet for most of human history, no adult could digest the stuff at all. Why can some adults drink milk and others cannot? Why did a liquid meant for infants become a global commodity? And how did a French chemist working on sour wine end up changing how the whole world stores it?

• 2. A Chance Mutation

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  Lactase is the enzyme needed to break down lactose, the sugar found only in milk and possibly in forsythia flowers and a few tropical shrubs. In the human small intestine, lactase reaches its highest levels immediately after birth, then begins a slow decline unless milk is consumed regularly. Originally, only children could digest milk, because adults stopped producing lactase. To cope, people converted milk to curd, cheese, and other products that reduce the levels of lactose. Thousands of years ago, a chance mutation spread in human populations in northwestern Europe. It allowed lactase production to continue into adulthood. This opened milk as a new source of nutrition that could sustain populations when other food sources failed. Adult digestion of milk relies on this lactase persistence, so lactose intolerant individuals have trouble with the sugar. The groups who kept tolerating milk grew inventive with the animals around them. They drew milk not only from cattle but from sheep, goats, yaks, water buffalo, horses, reindeer, and camels.

• 3. Out Of Southwest Asia

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  Humans first learned to consume the milk of other mammals after domesticating animals during the Neolithic Revolution. This happened independently in several places, from as early as 9000 to 7000 BC in Mesopotamia to 3500 to 3000 BC in the Americas. People domesticated the most important dairy animals, cattle, sheep, and goats, in Southwest Asia. Archaeologist Andrew Sherratt suggested dairying began much later, in a separate secondary products revolution in the fourth millennium BC. Recent findings do not support Sherratt's model. Analysis of lipid residue in prehistoric pottery shows dairying was practiced in the early phases of agriculture in Southwest Asia, by at least the seventh millennium BC. From there, domestic dairy animals spread to Europe beginning around 7000 BC, though they did not reach Britain and Scandinavia until after 4000 BC. They also spread to South Asia between 7000 and 5500 BC. Camels, domesticated in central Arabia in the fourth millennium BC, became dairy animals in North Africa and the Arabian Peninsula. In East and Southeast Asia, the Americas, and Australia, milk was historically not a large part of the diet. It became common there comparatively recently, a consequence of European colonialism over the last 500 years.

• 4. The Virtuous White Liquor

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  In the Middle Ages, milk was called the "virtuous white liquor," because alcoholic beverages were safer to drink than the water generally available. People incorrectly thought milk was blood diverted from the womb to the breast. So it was also known as "white blood," and treated like blood for religious dietary purposes and in humoral theory. James Rosier kept a record of the 1605 voyage that George Weymouth made to New England. It claimed the Wabanaki people Weymouth captured in Maine milked "Rain-Deere and Fallo-Deere." Journalist Avery Yale Kamila and food historians said Rosier "misinterpreted the evidence." Historians report the Wabanaki did not domesticate deer, and the tribes of the northern woodlands have historically made nut milk. Cows were imported to New England in 1624. The earliest Egyptian records of burn treatments describe burn dressings made from the milk of mothers of male babies.

• 5. Rails And Refrigeration

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  Mid-19th-century urban growth and the expanding railway network revolutionized milk supply. Individual railway firms began carrying milk from rural areas to London in the 1840s and 1850s. Possibly the first instance came in 1846, when St Thomas's Hospital in Southwark contracted with suppliers outside London to ship milk by rail. The Great Western Railway began moving milk into London from Maidenhead in 1860, despite much criticism. By 1900, that company was transporting over 25 million imperial gallons annually. Demand for milk in most parts of the country doubled or tripled over the last three decades of the 19th century. Legislation in 1875 made the adulteration of milk illegal. Marketing campaigns later reshaped its image, including the 1980s slogan "Milk: It does a body good" and the 1990s "got milk?" The proportion of London's milk arriving by rail grew from under 5% in the 1860s to over 96% by the early 20th century. Milk was also analyzed for tuberculosis. In 1907, 180 samples were tested in Birmingham, and 13.3% were found to be infected. Glass bottles for milk first appeared in the 1870s, and plastic-coated paper cartons arrived commercially in 1932.

• 6. Pasteur's Accident

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  In 1863, French chemist and biologist Louis Pasteur invented pasteurization, a method of killing harmful bacteria in beverages and food. He developed it while on summer vacation in Arbois, trying to remedy the frequent acidity of the local wines. He found it was enough to heat a young wine to only about 50 to 60 degrees Celsius for a brief time to kill the microbes. The wine could still age properly without losing quality. The process took his name in his honor. Commercial pasteurizing equipment was produced in Germany in the 1880s, and producers in Copenhagen and Stockholm adopted it by 1885. The standard high temperature short time process heats milk to 72 degrees Celsius for 15 seconds. This completely kills pathogenic bacteria, making the milk safe to drink for up to three weeks if continually refrigerated. Heating costs some nutrients. Soluble calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and vitamin C by 20% or greater. Ultra-heat treatment goes further, heating homogenized milk to 138 degrees Celsius for 2 to 4 seconds. That milk keeps for up to six months unopened and needs no refrigeration until the package is opened.

• 7. Inside The Drop

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  Milk is an emulsion of butterfat globules within a water-based fluid carrying dissolved carbohydrates, protein aggregates, and minerals. The pH of cow's milk ranges from 6.7 to 6.9. Full fat milk contains about 33 grams of fat per liter, including roughly 19 grams of saturated fat. Each fat globule is composed almost entirely of triacylglycerols and wrapped in a membrane of complex lipids and proteins, which keep the globules from coalescing. Normal bovine milk contains 30 to 35 grams of protein per liter, about 80% of it arranged in casein micelles. Each casein micelle is roughly spherical and about a tenth of a micrometer across, held together by nanometer-scale particles of calcium phosphate. Its outer layer is strands of kappa-casein, all carrying a negative charge that makes them repel each other and stay suspended. The proteins left in the whey, after caseins coagulate into curds, are the whey proteins, dominated by lactoglobulin. The ratio of caseins to whey proteins is 82:18 in cows and around 32:68 in humans. Lactose gives milk its sweet taste and contributes roughly 40% of the calories in whole cow's milk. Color comes from physics. Casein micelles scatter shorter-wavelength blue light more than red, giving fat-free skimmed milk a bluish tint.

• 8. Myth, Slang, And The Bath

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  In Greek mythology, the Milky Way formed after the trickster god Hermes suckled the infant Heracles at the breast of Hera, the queen of the gods, while she slept. When Hera awoke, she tore Heracles away and splattered her breast milk across the heavens. The Bible refers to the "Land of Milk and Honey" as a metaphor for the bounty of the Promised Land. The Qur'an asks readers to wonder at "pure milk palatable for the drinkers." A milksop once meant an "effeminate spiritless man," attested in the late 14th century. Milk toast, a dish of milk and toast, inspired the name of the timid comic strip character Caspar Milquetoast, drawn by H. T. Webster from 1924 to 1952. So "milquetoast" entered the language for a timid, apologetic person. In the 19th century, "milk" also named a cheap, poisonous drink of methylated spirits mixed with water. Beyond food, diluted milk solutions can prevent powdery mildew on grape vines without harming the plant. A milk bath uses lactic acid, an alpha hydroxy acid, to dissolve the proteins that hold skin together.