Ch.1: Milk and Dairy Products

Chapter 1 of the book "On Food and Cooking: The Science and Lore of the Kitchen" by Harold McGee (1984) Mammals and Milk Milk and Health Milk Biology and Chemistry Unfermented Dairy Products Fresh Fermented Milks and Creams Cheese

300 flashcards · Other · by lakesare

Part of Public › Books › On Food and Cooking (Harold McGee) · 16 courses

1. [Milk and Dairy Products] What does the word mammal literally mean?

   "Creature of the breast." Accordingly, the first food any mammal tastes is milk.

2. [Mammals and Milk] Besides milk, which features set mammals apart from reptiles?

   Warm blood, hair and skin glands. These features evolved together with milk.

3. [Mammals and Milk] How may milk have begun, about 300 million years ago?

   As a skin secretion that fed and protected hatchlings resting on the mother. Example: the platypus still feeds its young this way.

4. [Mammals and Milk] How did milk make the large human brain possible?

   Milk feeds the baby after birth, so the brain can keep growing outside the womb. A brain finished in the womb would be too big to pass through the birth canal. This is why human infants are helpless for months.

5. [Mammals and Milk] What is a ruminant?

   A grazing animal whose stomach holds fiber-digesting microbes, and which rechews its food. The stomach has several chambers and is about a fifth of the body weight; most of its trillions of microbes are in the first chamber, the rumen. The animal regurgitates partly digested food and chews it again.Example: cattle, sheep, goats, deer.

6. [Mammals and Milk] Which climate change, about 30 million years ago, favored the ruminants (cattle, sheep, goats, deer)?

   The climate turned dry for part of each year, and grasslands spread. In the dry season the grass is dry and fibrous; ruminants could live on it, while horses declined.

7. [Mammals and Milk] Why would there be no dairying without ruminants (cattle, sheep, goats)?

   Ruminants turn feed that humans can't eat (grass, straw) into plenty of milk. That feed can also be stored for winter.

8. [Mammals and Milk] Which wild animal is the ancestor of the dairy cow?

   The aurochs, a huge long-horned wild ox. The aurochs stood about 6 ft/180 cm at the shoulder and lived in Asia, Europe and North Africa.

9. [Mammals and Milk] Why are the main European dairy cows (Jersey, Holstein) smaller than their wild ancestor?

   They were bred to put their energy into milk, not muscle and bone. The breeding started about 5,000 years ago; the wild ancestor, the aurochs, stood about 180 cm at the shoulder.

10. [Mammals and Milk] Which animal's milk is true mozzarella made from?

    The water buffalo's. Buffalo milk has about 6.9% fat, cow's milk about 3.7%, so mozzarella made from cow's milk turns out quite different.

11. [Mammals and Milk] Which animal was probably the first, after the dog, to be domesticated?

    The goat, 9000 to 8000 BCE, in what is now Iran and Iraq.

12. [Mammals and Milk] Why is the goat such a useful dairy animal on poor farmland?

    A goat eats almost anything, even woody scrub, and gives the most milk for its size. No other dairy animal gives more milk per kilogram of body weight.

13. [Mammals and Milk] How rich is sheep's milk compared with cow's milk?

    About twice as fatty, and much richer in protein. Sheep 7.5% fat and 6.0% protein; cow 3.7% fat and 3.4% protein.

14. [Mammals and Milk] Which famous cheeses are made from sheep's milk?

    Roquefort, pecorino and feta.

15. [Mammals and Milk] Which dairy animal may have evolved rumination (rechewing fiber-rich food) independently of cattle, sheep and goats?

    The camel. Camel milk is roughly like cow's milk and is a staple food in northeast Africa.

16. [Mammals and Milk] Why was milking a big advance over keeping animals only for meat?

    A milked animal gives, every year for several years, at least as much food as its carcass would. And the food comes in small daily amounts. Dairying is the most efficient way to get food from land that is not farmed.

17. [Mammals and Milk] Which changes happen to milk simply kept in a container?

    Creaming Left to stand, milk forms a fat-rich layer of cream at the top. Churning Agitated cream turns into butter. Souring The rest of the milk turns acid and curdles into thick yogurt. Draining Draining the curdled milk separates solid curd from liquid whey. Salting Salted fresh curd is a simple cheese that keeps a long time.

18. [Mammals and Milk] What is koumiss?

    Mare's milk fermented into a lightly alcoholic drink. Made by the nomads of central Asia, who could not brew beer or make wine, since both need a settled life.

19. [Mammals and Milk] Why did cheese making flourish in northern Europe?

    Plenty of pasture for cattle, and a cool climate that allows long, slow fermentations.

20. [Mammals and Milk] Why may China never have taken up dairying?

    Where Chinese farming began, there were few grasses for grazing animals. The wild plants there were mostly relatives of wormwood and epazote, often toxic. This explanation is McGee's suggestion.

21. [Mammals and Milk] When did dairy animals first reach the Americas?

    In 1493, on Columbus's second voyage. Sheep, goats and Spanish longhorn cattle. The New World had no dairying before then.

22. [Mammals and Milk] Why was city milk in early Victorian times a major cause of child deaths?

    Cows were kept in city stalls on brewery waste, and the milk was watered down and dirty. It was also adulterated and sold from open containers. From about 1830, railroads brought fresh country milk and laws began regulating milk quality.

23. [Mammals and Milk] Which two big changes in dairying did Louis Pasteur inspire?

    Pasteurization A heat treatment that kills pathogens. Pure starter cultures Standard, purified microbial cultures for making cheese and other fermented foods.

24. [Mammals and Milk] Why does modern milk lack the color, flavor and seasonal changes of old-fashioned milk?

    Nearly all of it comes from one breed (Holstein) fed a uniform diet with little fresh grass. Holstein-Friesians are 90% of American and 85% of British dairy cattle.

25. [Milk and Health] Which nutrients is milk particularly rich in?

    Protein, sugar, fat, vitamin A, the B vitamins and calcium. Unlike most foods, milk is made to be a food: the calf's only food early in life.

26. [Milk and Health] What does the word lady have in common with dairy?

    Both come from a root meaning "to knead bread". Dairy was dey-ery, the room where the dey (woman servant) made butter and cheese; dey comes from that root.

27. [Milk and Health] Why does cow's milk contain more than twice the protein and minerals of human milk?

    Calves grow faster than babies, so they need more of both. A calf doubles its birth weight in 50 days, a human infant in 100.

28. [Milk and Health] In which two major nutrients is cow's milk poor?

    Iron and vitamin C.

29. [Milk and Health] Why is the milk fat of cows, sheep and goats so saturated?

    Microbes in their stomachs saturate the fats from grass and grain. They turn unsaturated fatty acids into saturated ones. Of common food fats, only coconut oil is more saturated.

30. [Milk and Health] How does human milk differ from cow's milk in protein and sugar?

    Human milk has a third of the protein and more sugar (lactose). Protein 1.1% vs. 3.4%; lactose 6.8% vs. 4.8%. Fat is similar (4.0% vs. 3.7%).

31. [Milk and Health] Which is the fattiest milk: cow, sheep, reindeer or fin whale?

    Fin whale milk: 42% fat. Reindeer 17%, sheep 7.5%, cow 3.7%. Fin whale milk is only 43% water.

32. [Milk and Health] Why do doctors advise against plain cow's milk for babies under one year?

    Too much protein, too little iron and unsaturated fat, and it can cause an allergy. Formula milks approximate breast milk better.

33. [Milk and Health] How does a baby develop an allergy to cow's milk protein?

    Protein fragments leak through the immature gut into the blood, and the immune system reacts to them. The reaction grows stronger with each feeding. 1% to 10% of American infants are affected; most children outgrow the allergy.

34. [Milk and Health] Which enzyme must split milk sugar (lactose) before the body can absorb it?

    Lactase, in the small intestine. Lactase splits lactose into its two simple sugars.

35. [Milk and Health] How does the activity of lactase (the enzyme that digests milk sugar) change with age?

    It peaks just after birth and falls to a low level by age 2 to 5. Most mammals never meet lactose again after weaning, so making the enzyme would waste resources.

36. [Milk and Health] What happens when an adult with little lactase (the enzyme that digests milk sugar) drinks a lot of milk?

    Bloating and diarrhea: gut bacteria ferment the sugar into gas. Undigested lactose reaches the large intestine, where bacteria make CO2\mathrm{CO_2}CO2​ , hydrogen and methane, and the sugar draws in water. This is lactose intolerance.

37. [Milk and Health] Is digesting milk sugar as an adult the rule or the exception among humans?

    The exception. It arose by a genetic change several thousand years ago, mainly in northern Europe.Example: lactose-tolerant adults are about 98% of Scandinavians, 90% of French and Germans, 40% of southern Europeans, 30% of African Americans.

38. [Milk and Health] What ways of eating dairy products work for lactose-intolerant adults?

    Small amounts of milk About a cup (250 ml) of milk a day usually causes no severe symptoms. Cheese Contains little or no lactose: most leaves with the whey, and bacteria and molds ferment the rest. Yogurt Its bacteria make lactose-digesting enzymes that stay active in the human small intestine. Added lactase Liquid lactase made from the fungus Aspergillus, a few drops added just before eating.

39. [Milk and Health] What two materials are bones built from?

    A protein framework, filled with hard calcium phosphate. Bone is constantly broken down and rebuilt throughout adult life, so it needs a steady supply of both.

40. [Milk and Health] What is osteoporosis?

    Loss of bone mass that makes fractures likely. Common in women after menopause. Dietary calcium helps prevent it.

41. [Milk and Health] Does drinking lots of milk clearly prevent osteoporosis (bone loss)?

    No: China and Japan drink little milk but have fewer fractures than the US. This is McGee's 2004 argument against the US advice of a quart (liter) of milk a day; he recommends a balanced diet and exercise.McGee: not "a single large white bullet".

42. [Milk and Health] Which two features of the modern diet make the body lose calcium in the urine?

    Much salt, and much animal protein. Sulfur-containing amino acids in animal protein make the urine acidic, and calcium salts are drawn from bone to neutralize it.

43. [Milk and Health] What does vitamin D do for bones?

    It lets the gut absorb calcium from food. It also influences bone building. Sources: fortified milk, eggs, fish, and our own skin in sunlight.

44. [Milk and Health] Name calcium-rich foods besides dairy products.

    Dried beans, nuts, tofu, corn tortillas, and greens such as kale. Tofu and tortillas are made with calcium salts.

45. [Milk and Health] Can fragments of digested milk protein act like hormones?

    Yes, some do. Example: one lowers breathing and heart rates, one triggers insulin release. Whether cow's-milk fragments matter for humans is unknown.

46. [Milk Biology and Chemistry] What is the usual yearly cycle of a dairy cow?

    Calve, milk for 10 months, rest 2 months, calve again. She is bred again 90 days after calving. A cow must give birth before giving much milk.

47. [Milk Biology and Chemistry] How much milk can a top modern dairy cow give per day?

    About 58 liters (15 gallons). The American average is about half that. Dairy sheep and goats give about 4 liters a day.

48. [Milk Biology and Chemistry] What is silage?

    Cattle feed made of chopped plants (often corn) fermented in an airtight silo.

49. [Milk Biology and Chemistry] What is colostrum?

    The first milk after birth: thick, yellow and rich in antibodies. It is also concentrated in fat, vitamins and other proteins.

50. [Milk Biology and Chemistry] Which milk components does the udder make itself, rather than take straight from the blood?

    The fat, the sugar (lactose) and the proteins. Secretory cells release proteins and fat globules into small compartments draining towards the teat; each fat globule leaves wrapped in part of the cell's outer membrane.

51. [Milk Biology and Chemistry] What is still alive or active in fresh raw milk?

    Living white blood cells and bacteria, and many working enzymes. Pasteurization stops most of this. Raw milk's activity helps ripen and flavor traditional cheeses.

52. [Milk Biology and Chemistry] What makes milk opaque white?

    Fat droplets and protein bundles just big enough to scatter light.

53. [Milk Biology and Chemistry] The pH of fresh milk is between 6.5 and 6.7, so milk is slightly acidic.

54. [Milk Biology and Chemistry] What gives milk and undyed butter their yellow color?

    Carotenes, yellow-orange pigments from fresh green feed. They dissolve in the milk fat.

55. [Milk Biology and Chemistry] Why is Jersey cow milk golden, while sheep and goat milk is white?

    Sheep and goats turn the yellow carotene from grass into colorless vitamin A; Jerseys don't. Jerseys convert only a little of it. Guernseys are like Jerseys; water buffalo are like sheep and goats.

56. [Milk Biology and Chemistry] Which vitamin sometimes gives skim milk or yogurt whey a greenish tint?

    Riboflavin.

57. [Milk Biology and Chemistry] What two sugars is lactose (milk sugar) made of?

    Glucose and galactose, joined together. The prefix lac- comes from the Greek word for milk.

58. [Milk Biology and Chemistry] Where in an animal's body is lactose (milk sugar) made?

    Only in the milk-making cells of the udder or breast.

59. [Milk Biology and Chemistry] What share of milk's calories comes from lactose (milk sugar)?

    Nearly half in human milk, 40% in cow's milk.

60. [Milk Biology and Chemistry] Why do lactic acid bacteria grow in milk faster than other microbes?

    They already have the enzymes to digest milk sugar. Most other microbes first have to make these enzymes. Examples: Lactobacillus, Lactococcus.

61. [Milk Biology and Chemistry] Why does soured milk resist spoiling?

    Its lactic acid is too sour for most other microbes. That includes many that would spoil the milk or cause disease.

62. [Milk Biology and Chemistry] How sweet is lactose (milk sugar) compared with table sugar?

    About one-fifth as sweet.

63. [Milk Biology and Chemistry] Why can condensed milk and ice cream turn sandy?

    Lactose (milk sugar) dissolves poorly, so it easily forms crystals. It is only a tenth as soluble in water as table sugar (200 vs. 2,000 g/l).

64. [Milk Biology and Chemistry] What share of the calories in whole milk comes from its fat?

    About half. The fat also carries the vitamins A, D, E and K. Cows make richer milk in winter; Jersey and Guernsey milk is especially rich.

65. [Milk Biology and Chemistry] What is the thin membrane around each fat droplet in milk made of?

    Phospholipids (emulsifiers) and proteins. The membrane is only a few molecules thick.

66. [Milk Biology and Chemistry] What does the membrane around each fat droplet in milk do?

    It keeps droplets from merging, and shields the fat from enzymes that would make it rancid. Fat globules (large spheres) among casein bundles and single whey protein molecules.

67. [Milk Biology and Chemistry] What is creaming?

    Fat droplets rising in standing milk to form a layer of cream on top. Homogenization prevents creaming.

68. [Milk Biology and Chemistry] Why does cream rise much faster than single fat droplets would?

    Some milk proteins glue the droplets into big clusters, which rise fast. A cluster holds about a million droplets. Heat damages these proteins, so pasteurized unhomogenized milk creams slowly. Goat, sheep and buffalo milk barely separate.

69. [Milk Biology and Chemistry] Why can cream be boiled down for hours without turning oily?

    Heat makes milk proteins stick to the fat droplets, thickening their protective coats. This makes cream sauces and reduced-milk sweets possible.

70. [Milk Biology and Chemistry] What happens when cream that was frozen and thawed is heated?

    It turns oily. Ice and fat crystals tear the droplet membranes; on thawing, droplets stick into butter grains, which melt into oil when heated.

71. [Milk Biology and Chemistry] What are the two main groups of milk proteins?

    Caseins, which clump in acid, and whey proteins, which stay dissolved. In cow's milk, caseins outweigh whey proteins 4 to 1.

72. [Milk Biology and Chemistry] Why doesn't boiling fresh milk curdle it, the way heat sets eggs?

    Milk proteins tolerate heat; milk curdles on heating only once it has turned sour.

73. [Milk Biology and Chemistry] What is a casein micelle?

    A tiny bundle of a few thousand casein (milk protein) molecules. Protein molecules (lines) held together by calcium phosphate particles (small spheres).About 1/10,000 mm across, 1/50 the size of a fat droplet; micelles take up about a tenth of milk's volume.

74. [Milk Biology and Chemistry] What holds a casein micelle (a bundle of milk proteins) together?

    Calcium, plus water-avoiding parts of the proteins sticking to each other. Calcium binds 15 to 25 casein molecules into a cluster, then several hundred clusters into a micelle.

75. [Milk Biology and Chemistry] How does kappa-casein keep casein micelles (bundles of milk proteins) apart?

    It covers each micelle with charged strands that repel other micelles. Kappa-casein caps the micelle at a certain size; its free end sticks out into the liquid as a negatively charged "hairy layer".

76. [Milk Biology and Chemistry] What happens to the casein micelles (bundles of milk proteins) as milk sours?

    Near pH 5.5 Kappa-casein's negative charge is neutralized, so micelles stop repelling each other and gather in loose clusters; the calcium holding them together dissolves and the micelles fall apart. From about pH 4.7 The scattered caseins lose their negative charge and bond into a continuous fine network: the milk curdles. Example: yogurt and sour cream are made this way, by acid-producing bacteria.

77. [Milk Biology and Chemistry] How does chymosin, the calf-stomach enzyme used in cheese making, curdle milk?

    It cuts off the repelling strands of the casein micelles, so they clump without acid. The strands are the protruding part of kappa-casein. McGee: chymosin gives the casein micelles "a haircut".

78. [Milk Biology and Chemistry] Which is by far the most abundant whey protein?

    Lactoglobulin. Its biological function is unknown. The other whey proteins include defensive proteins and enzymes.

79. [Milk Biology and Chemistry] Why does cooked milk smell slightly of sulfur?

    Heat unfolds the main whey protein, which then releases hydrogen sulfide. Lactoglobulin unfolds at 172°F/78°C, exposing sulfur atoms that form H2S\mathrm{H_2S}H2​S .

80. [Milk Biology and Chemistry] Why do whey proteins clot in hot acidic whey, but not in boiling milk?

    In milk they stick to the casein bundles; in whey, with little casein, they stick to each other. Example: true ricotta is made from these whey clots.

81. [Milk Biology and Chemistry] Why are milk and cream usually cooked before making milk foams or ice cream?

    Heat-unfolded whey proteins hold air bubbles and ice crystals better.

82. [Milk Biology and Chemistry] What gives fresh milk its taste?

    Sweetness from lactose, slight saltiness from minerals, and a trace of acidity.

83. [Milk Biology and Chemistry] What gives fresh milk its mild aroma?

    Mainly short-chain fatty acids, small enough to evaporate. Example: butyric and capric acid (4 to 12 carbons). These fatty acids also keep the very saturated milk fat fluid at body temperature.

84. [Milk Biology and Chemistry] What causes the distinctive smell of goat and sheep milk?

    Two branched fatty acids that cow's milk lacks. 4-ethyl-octanoic and 4-methyl-octanoic acid, each with 8 carbons.

85. [Milk Biology and Chemistry] How does the cow's feed change milk flavor?

    Hay and silage give a simple, mildly cheesy aroma; fresh pasture a richer, raspberry and barnyard one.

86. [Milk Biology and Chemistry] How does heating change the flavor of milk?

    Low-temperature pasteurization Some delicate aromas evaporate, and faint notes of sulfur and green leaves appear (dimethyl sulfide, hexanal). Above 170°F/76°C Traces of vanilla, almond and cultured-butter aromas, and eggy hydrogen sulfide. Prolonged boiling Maillard (browning) reactions between lactose and milk proteins give a butterscotch flavor.

87. [Milk Biology and Chemistry] What causes cardboard, metallic or fishy off-flavors in milk?

    Oxygen or strong light damaging the fats in the droplet membranes. The fats are phospholipids, which oxidize.

88. [Milk Biology and Chemistry] Why does milk in a clear bottle under shop lights develop a cabbage-like taste?

    Light makes the vitamin riboflavin react with an amino acid (methionine). Sunlight and fluorescent light both do it; opaque cartons prevent it.

89. [Unfermented Dairy Products] Why was raw milk so dangerous in 18th- and 19th-century cities?

    Germs from sick cows or dirty handling multiply fast in milk, and city milk came from far away. It was also often watered down or adulterated. Many children died of tuberculosis, undulant fever and food poisoning from tainted milk.McGee: "the udder hangs right next to the tail".

90. [Unfermented Dairy Products] For which foods was pasteurization originally developed, in the 1860s?

    Wine and beer, by Louis Pasteur. A moderate heat treatment that preserves the drink while changing its flavor little. Dairies adopted it only decades later.

91. [Unfermented Dairy Products] Why is pasteurization a necessity in industrial dairying?

    Milk pooled from many farms and pumped through machinery has many chances to pick up germs. One contaminated farm can spoil a whole batch.

92. [Unfermented Dairy Products] In which two ways does pasteurization make milk keep longer?

    It kills microbes, and it stops milk's own enzymes, which slowly make it taste bad. The most harmful enzymes split fats. Pasteurized milk kept below 40°F/5°C stays drinkable for 10 to 18 days.

93. [Unfermented Dairy Products] What are the three basic methods of pasteurizing milk, with their temperatures and times?

    Batch pasteurization Milk is stirred in a vat for 30 to 35 minutes at 145°F/62°C or more; flavor changes only a little. High-temperature, short-time (HTST) The industrial standard: milk flows without stopping through a heat exchanger and stays at 162°F/72°C or above for 15 seconds. Ultra-high temperature (UHT) 265 to 300°F/130 to 150°C, instantaneously or for 1 to 3 seconds; with sterile packaging the milk keeps for months unrefrigerated.

94. [Unfermented Dairy Products] Why do U.S. dairies often pasteurize milk hotter than needed?

    American drinkers have come to expect the slightly cooked flavor that extra heat gives. Often 171°F/77°C instead of the minimum 162°F/72°C. The heat unfolds some whey proteins, which release smelly hydrogen sulfide; this was once seen as a defect.

95. [Unfermented Dairy Products] Why does UHT heating (very hot, very brief) change cream less than milk?

    Cream has less of the sugar and protein that react to give a cooked flavor and brown color. For comparison, sterilized milk (230 to 250°F/110 to 121°C for 8 to 30 minutes) is darker and stronger-flavored than UHT milk, and keeps indefinitely at room temperature.

96. [Unfermented Dairy Products] What does homogenization of milk prevent?

    The cream rising to the top. Homogenization was developed in France around 1900.

97. [Unfermented Dairy Products] How is milk homogenized?

    Hot milk is forced at high pressure through tiny nozzles, which tears its fat droplets apart. Average droplet diameter falls from about 4 micrometers to about 1.Example: one 4 μm droplet has the volume of 43=644^3 = 6443=64 droplets of 1 μm, close to the roughly sixty-fold increase in droplet number.

98. [Unfermented Dairy Products] Why does the fat in homogenized milk no longer rise as cream?

    Casein particles coat the new small fat droplets, weighing them down and keeping them apart. The original droplet membranes are too little to cover the much larger total surface. The droplets end up carrying roughly one third of all the casein.

99. [Unfermented Dairy Products] Why is milk always pasteurized just before or during homogenization?

    Otherwise milk enzymes would attack the briefly unprotected fat and make it rancid.

100. [Unfermented Dairy Products] How does homogenization change the taste and look of milk?

     Blander Probably because flavor molecules stick to the new fat-globule surfaces. More resistant to off-flavors It develops most off-flavors less readily. Creamier in the mouth It has around sixty times as many fat globules. Whiter The carotenoid pigments in the fat are spread over smaller, more numerous particles.