On Food And Cooking Part 8

But these rules wouldn't work for young goat cheeses (white and coatless), Roquefort (with its pockets of whey), Emmental (eyefull and light), or Camembert (which should give when thumbed). As always, the proof is in the tasting.

These days, the most important thing is to understand that bulk supermarket cheeses are only pale (or dyed) imitations of their more flavorful, distinctive originals. The way to find good cheeses is to buy from a specialist who loves and knows them, chooses the best and takes good care of them, and offers samples for tasting.

Cut to Order Whenever possible, buy portions that are cut while you watch. Precut portions may be days or weeks old, and their large exposed surfaces inevitably develop rancid flavors from contact with air and plastic wrap. Exposure to light in the dairy case also damages lipids and causes off-flavors in as little as two days; in addition it bleaches the annatto in orange-dyed cheeses, turning it pink. Pregrated cheese has a tremendous surface area, and while it is often carefully wrapped, it loses much of its aroma and its carbon dioxide, which also contributes the impression of staleness. Whenever possible, buy portions that are cut while you watch. Precut portions may be days or weeks old, and their large exposed surfaces inevitably develop rancid flavors from contact with air and plastic wrap. Exposure to light in the dairy case also damages lipids and causes off-flavors in as little as two days; in addition it bleaches the annatto in orange-dyed cheeses, turning it pink. Pregrated cheese has a tremendous surface area, and while it is often carefully wrapped, it loses much of its aroma and its carbon dioxide, which also contributes the impression of staleness.

Cool, Not Cold If cheese must be kept for more than a few days, it's usually easiest to refrigerate it. Unfortunately, the ideal conditions for holding cheese - a humid 5560F/1215C, simply a continuation of its ripening conditions - is warmer than most refrigerators, and cooler and moister than most rooms. Refrigeration essentially puts cheese into suspended animation, so if you want an immature soft cheese to ripen further, you'll need to keep it warmer. If cheese must be kept for more than a few days, it's usually easiest to refrigerate it. Unfortunately, the ideal conditions for holding cheese - a humid 5560F/1215C, simply a continuation of its ripening conditions - is warmer than most refrigerators, and cooler and moister than most rooms. Refrigeration essentially puts cheese into suspended animation, so if you want an immature soft cheese to ripen further, you'll need to keep it warmer.

Cheeses should never be served direct from the refrigerator. At such low temperatures the milk fat is congealed and as hard as refrigerated b.u.t.ter, the protein network unnaturally stiff, the flavor molecules imprisoned, and the cheese will seem rubbery and flavorless. Room temperature is best, unless it's so warm (above about 80F/26C) that the milk fat will melt and sweat out of the cheese.

Cheese CrystalsCheeses usually have such a smooth, luscious texture, either from the beginning or as a hard cheese melts in the mouth, that an occasional crunch comes as a surprise. In fact a number of cheeses develop hard, salt-like crystals of various kinds. The white crystals often visible against the blue mold of a Roquefort, or detectable in the rind of a Camembert, are calcium phosphate, deposited because the Penicillium Penicillium molds have made the cheese less acid and calcium salts less soluble. In aged Cheddar there are often crystals of calcium lactate, formed when ripening bacteria convert the usual form of lactic acid into its less soluble mirror ("D") image. In Parmesan, Gruyere, and aged Gouda, the crystals may be calcium lactate or else tyrosine, an amino acid produced by protein breakdown that has limited solubility in these low-moisture cheeses. molds have made the cheese less acid and calcium salts less soluble. In aged Cheddar there are often crystals of calcium lactate, formed when ripening bacteria convert the usual form of lactic acid into its less soluble mirror ("D") image. In Parmesan, Gruyere, and aged Gouda, the crystals may be calcium lactate or else tyrosine, an amino acid produced by protein breakdown that has limited solubility in these low-moisture cheeses.

Loose Wrapping Tight wrapping in plastic film is inadvisable for three reasons: trapped moisture and restricted oxygen encourages the growth of bacteria and molds, not always the cheese's own; strong volatiles such as ammonia that would otherwise diffuse from the cheese instead impregnate it; and trace volatile compounds and plastic chemicals migrate into the cheese. Whole, still-developing cheeses should be stored unwrapped or very loosely wrapped, other cheeses loosely wrapped in wax paper. Stand them on a wire rack or turn them frequently to prevent the bottom from getting soggy. It can be fun to play the role of Tight wrapping in plastic film is inadvisable for three reasons: trapped moisture and restricted oxygen encourages the growth of bacteria and molds, not always the cheese's own; strong volatiles such as ammonia that would otherwise diffuse from the cheese instead impregnate it; and trace volatile compounds and plastic chemicals migrate into the cheese. Whole, still-developing cheeses should be stored unwrapped or very loosely wrapped, other cheeses loosely wrapped in wax paper. Stand them on a wire rack or turn them frequently to prevent the bottom from getting soggy. It can be fun to play the role of affineur affineur and encourage surface or blue mold from a good Camembert or Roquefort to grow on a fresh goat cheese or in a piece of standard Cheddar. But there's some risk that other microbes will join in. If a piece of cheese develops an unusual surface mold or sliminess or an unusual odor, the safest thing is to discard it. Simply tr.i.m.m.i.n.g the surface will not remove mold filaments, which can penetrate some distance and may carry toxins (p. 67). and encourage surface or blue mold from a good Camembert or Roquefort to grow on a fresh goat cheese or in a piece of standard Cheddar. But there's some risk that other microbes will join in. If a piece of cheese develops an unusual surface mold or sliminess or an unusual odor, the safest thing is to discard it. Simply tr.i.m.m.i.n.g the surface will not remove mold filaments, which can penetrate some distance and may carry toxins (p. 67).

Rinds Should cheese rinds be eaten? It depends on the cheese and the eater. The rinds of long-aged cheeses are generally tough and slightly rancid, and are best avoided. With softer cheeses it's largely a matter of taste. The rind can offer an interesting contrast to the interior in both flavor and texture. But if safety is a concern, then consider the rind a protective coating and trim it off. Should cheese rinds be eaten? It depends on the cheese and the eater. The rinds of long-aged cheeses are generally tough and slightly rancid, and are best avoided. With softer cheeses it's largely a matter of taste. The rind can offer an interesting contrast to the interior in both flavor and texture. But if safety is a concern, then consider the rind a protective coating and trim it off.

Cooking with Cheese When used as an ingredient in cooking, cheese can add both flavor and texture: either unctuousness or crispness, depending on circ.u.mstances. In most cases, we want the cheese to melt and either mix evenly with other ingredients or spread over a surface. A certain giving cohesiveness is part of the pleasure of melted cheese. Stringy cheese can be enjoyable on pizzas, but a nuisance in more formal dishes. To understand cheese cooking, we need to understand the chemistry of melting.

Cheese Melting What is going on when we melt a piece of cheese? Essentially two things. First, at around 90F, the milk fat melts, which makes the cheese more supple, and often brings little beads of melted fat to the surface. Then at higher temperatures - around 130F/55C for soft cheeses, 150F/65C for Cheddar and Swiss types, 180F/82C for Parmesan and pecorino - enough of the bonds holding the casein proteins together are broken that the protein matrix collapses, and the piece sags and flows as a thick liquid. Melting behavior is largely determined by water content. Low-moisture hard cheeses require more heat to melt because their protein molecules are more concentrated and so more intimately bonded to each other; and when melted, they flow relatively little. Separate pieces of grated moist mozzarella will melt together, while flecks of Parmesan remain separate. With continued exposure to high heat, moisture will evaporate from the liquefied cheese, which gets progressively stiffer and eventually resolidifies. Most cheeses will leak some melted fat, and extensive breakdown of the protein fabric accentuates this in high-fat cheeses. The ratio of fat to surrounding protein is just 0.7 in part-skim Parmesan, around 1 in mozzarella and the alpine cheeses, but 1.3 in Roquefort and Cheddar, which are especially p.r.o.ne to exuding fat when melted. What is going on when we melt a piece of cheese? Essentially two things. First, at around 90F, the milk fat melts, which makes the cheese more supple, and often brings little beads of melted fat to the surface. Then at higher temperatures - around 130F/55C for soft cheeses, 150F/65C for Cheddar and Swiss types, 180F/82C for Parmesan and pecorino - enough of the bonds holding the casein proteins together are broken that the protein matrix collapses, and the piece sags and flows as a thick liquid. Melting behavior is largely determined by water content. Low-moisture hard cheeses require more heat to melt because their protein molecules are more concentrated and so more intimately bonded to each other; and when melted, they flow relatively little. Separate pieces of grated moist mozzarella will melt together, while flecks of Parmesan remain separate. With continued exposure to high heat, moisture will evaporate from the liquefied cheese, which gets progressively stiffer and eventually resolidifies. Most cheeses will leak some melted fat, and extensive breakdown of the protein fabric accentuates this in high-fat cheeses. The ratio of fat to surrounding protein is just 0.7 in part-skim Parmesan, around 1 in mozzarella and the alpine cheeses, but 1.3 in Roquefort and Cheddar, which are especially p.r.o.ne to exuding fat when melted.

Nonmelting Cheeses There are several kinds of cheese that do not melt on heating: they simply get drier and stiffer. These include Indian paneer and Latin queso blanco, Italian ricotta, and most fresh goat cheeses; all of them are curdled exclusively or primarily by means of acid, not rennet. Rennet creates a malleable structure of large casein micelles held together by relatively few calcium atoms and hydrophobic bonds, so this structure is readily weakened by heat. Acid, on the other hand, dissolves the calcium glue that holds the casein proteins together in micelles (p. 20), and it eliminates each protein's negative electrical charge, which would otherwise cause the proteins to repel each other. The proteins are free to flock together and bond extensively into microscopic clumps. So when an acid curd is heated, the first thing to be shaken loose is not the proteins, but water: the water boils away, and this simply dries out and concentrates the protein even further. This is why firm paneer and queso blanco can be simmered or fried like meat, and goat cheeses and ricotta maintain their shape on pizzas or in pasta stuffings. There are several kinds of cheese that do not melt on heating: they simply get drier and stiffer. These include Indian paneer and Latin queso blanco, Italian ricotta, and most fresh goat cheeses; all of them are curdled exclusively or primarily by means of acid, not rennet. Rennet creates a malleable structure of large casein micelles held together by relatively few calcium atoms and hydrophobic bonds, so this structure is readily weakened by heat. Acid, on the other hand, dissolves the calcium glue that holds the casein proteins together in micelles (p. 20), and it eliminates each protein's negative electrical charge, which would otherwise cause the proteins to repel each other. The proteins are free to flock together and bond extensively into microscopic clumps. So when an acid curd is heated, the first thing to be shaken loose is not the proteins, but water: the water boils away, and this simply dries out and concentrates the protein even further. This is why firm paneer and queso blanco can be simmered or fried like meat, and goat cheeses and ricotta maintain their shape on pizzas or in pasta stuffings.

Stringiness Melted cheese becomes stringy when mostly intact casein molecules are cross-linked together by calcium into long, rope-like fibers that can stretch but get stuck to each other. If the casein has been attacked extensively by ripening enzymes, then the pieces are too small to form fibers; so well-aged grating cheeses don't get stringy. The degree of cross-linking also matters: a lot and the casein molecules are so tightly bound to each other that they can't give with pulling, and simply snap apart; a little and they pull apart right away. The cross-linking is determined by how the cheese was made: high acidity removes calcium from the curd, and high moisture, high fat, and high salt help separate casein molecules from each other. So the stringiest cheeses are moderate in acidity, moisture, salt, and age. The most common stringy cheeses are intentionally fibrous mozzarella, elastic Emmental, and Cheddar. Crumbly cheeses like Ches.h.i.+re and Leicester, and moist ones like Caerphilly, Colby, and Jack are preferred for making such melted preparations as Welsh rarebit, stewed cheese, and grilled-cheese sandwiches. Similarly, Emmental's alpine cousin Gruyere is preferred in fondues because it's moister, fatter, and saltier. And the Italian grating cheeses - Parmesan, grana Padano, the pecorinos - have had their protein fabric sufficiently broken that its pieces readily disperse in sauces, soups, risottos, polenta, and pasta dishes. Melted cheese becomes stringy when mostly intact casein molecules are cross-linked together by calcium into long, rope-like fibers that can stretch but get stuck to each other. If the casein has been attacked extensively by ripening enzymes, then the pieces are too small to form fibers; so well-aged grating cheeses don't get stringy. The degree of cross-linking also matters: a lot and the casein molecules are so tightly bound to each other that they can't give with pulling, and simply snap apart; a little and they pull apart right away. The cross-linking is determined by how the cheese was made: high acidity removes calcium from the curd, and high moisture, high fat, and high salt help separate casein molecules from each other. So the stringiest cheeses are moderate in acidity, moisture, salt, and age. The most common stringy cheeses are intentionally fibrous mozzarella, elastic Emmental, and Cheddar. Crumbly cheeses like Ches.h.i.+re and Leicester, and moist ones like Caerphilly, Colby, and Jack are preferred for making such melted preparations as Welsh rarebit, stewed cheese, and grilled-cheese sandwiches. Similarly, Emmental's alpine cousin Gruyere is preferred in fondues because it's moister, fatter, and saltier. And the Italian grating cheeses - Parmesan, grana Padano, the pecorinos - have had their protein fabric sufficiently broken that its pieces readily disperse in sauces, soups, risottos, polenta, and pasta dishes.

Cheeses are at their stringiest right around their melting point - which usually means right about the point that a piping hot dish gets cool enough to eat - and get more so the more they are stirred and stretched. One French country dish, aligot aligot from the Auvergne, calls for unripened Cantal cheese to be sliced, mixed with just-boiled potatoes, and sweepingly stirred until it forms an elastic cord that can stretch for 6 to 10 feet/23 meters! from the Auvergne, calls for unripened Cantal cheese to be sliced, mixed with just-boiled potatoes, and sweepingly stirred until it forms an elastic cord that can stretch for 6 to 10 feet/23 meters!

Cheese Sauces and Soups When cheese is used to bring flavor and richness to a sauce (Gruyere or Parmesan in French When cheese is used to bring flavor and richness to a sauce (Gruyere or Parmesan in French sauce Mornay, sauce Mornay, Fontina in Italian Fontina in Italian fonduta fonduta) or a soup, the aim is to integrate the cheese evenly into the liquid. There are several ways to avoid the stringiness, lumps, and fat separation that result when the cheese proteins are allowed to coagulate.

Avoid using a cheese that is p.r.o.ne to stringiness in the first place. Moist or well-aged grating cheeses blend better.

Grate the cheese finely so that you can disperse it evenly throughout the dish from the beginning.

Heat the dish as little as possible after the cheese has been added. Simmer the other ingredients together first, let the pot cool a bit, and then then add the cheese. Remember that temperatures above the cheese's melting point will tend to tighten the protein patches into hard clumps and squeeze out their fat. On the other hand, don't let the dish cool down too much before serving. Cheese gets stringier and tougher as it cools down and congeals. add the cheese. Remember that temperatures above the cheese's melting point will tend to tighten the protein patches into hard clumps and squeeze out their fat. On the other hand, don't let the dish cool down too much before serving. Cheese gets stringier and tougher as it cools down and congeals.

Minimize stirring, which can push the dispersed patches of cheese protein back together into a big sticky ma.s.s.

Include starchy ingredients that will coat the protein patches and fat pockets and keep them apart. These stabilizing ingredients include flour, cornstarch, and arrowroot.

If the flavor of the dish permits, include some wine or lemon juice - a preventive or emergency measure well known to fans of the ultimate cheese sauce, fondue. fondue.

Cheese Fondue In the Swiss Alps, where for centuries cheese has been melted in a communal pot at the table and kept hot over a flame for dipping bread, it's well known that wine can help keep melted cheese from getting stringy or seizing up. The ingredients in a cla.s.sic fondue, in fact, are just alpine cheese - usually Gruyere - a In the Swiss Alps, where for centuries cheese has been melted in a communal pot at the table and kept hot over a flame for dipping bread, it's well known that wine can help keep melted cheese from getting stringy or seizing up. The ingredients in a cla.s.sic fondue, in fact, are just alpine cheese - usually Gruyere - a tart tart white wine, some kirsch, and sometimes (for added insurance) starch. The combination of cheese and wine is delicious but also savvy. The wine contributes two essential ingredients for a smooth sauce: water, which keeps the casein proteins moist and dilute, and tartaric acid, which pulls the cross-linking calcium off of the casein proteins and binds tightly to it, leaving them glueless and happily separate. (Alcohol has nothing to do with fondue stability.) The citric acid in lemon juice will do the same thing. If it's not too far gone, you can sometimes rescue a tightening cheese sauce with a squeeze of lemon juice or a splash of white wine. white wine, some kirsch, and sometimes (for added insurance) starch. The combination of cheese and wine is delicious but also savvy. The wine contributes two essential ingredients for a smooth sauce: water, which keeps the casein proteins moist and dilute, and tartaric acid, which pulls the cross-linking calcium off of the casein proteins and binds tightly to it, leaving them glueless and happily separate. (Alcohol has nothing to do with fondue stability.) The citric acid in lemon juice will do the same thing. If it's not too far gone, you can sometimes rescue a tightening cheese sauce with a squeeze of lemon juice or a splash of white wine.

Toppings, Gratins When a thin layer of cheese is heated in the oven or under a broiler - on a gratin, a pizza, or bruschetta - the intense heat can quickly dehydrate the casein fabric, toughen it, and cause its fat to separate. To avoid this, watch the dish carefully and remove it as soon as the cheese melts. On the other hand, browned, crisp cheese is quite delicious: the When a thin layer of cheese is heated in the oven or under a broiler - on a gratin, a pizza, or bruschetta - the intense heat can quickly dehydrate the casein fabric, toughen it, and cause its fat to separate. To avoid this, watch the dish carefully and remove it as soon as the cheese melts. On the other hand, browned, crisp cheese is quite delicious: the religieuse religieuse at the bottom of the fondue pot crowns the meal. If you want a cheese topping to brown, then pick a robust cheese that resists fat loss and stringiness. The grating cheeses are especially versatile; Parmesan can be formed into a thin disk and melted and lightly browned in a frying pan or the oven, then molded into cups or other shapes. at the bottom of the fondue pot crowns the meal. If you want a cheese topping to brown, then pick a robust cheese that resists fat loss and stringiness. The grating cheeses are especially versatile; Parmesan can be formed into a thin disk and melted and lightly browned in a frying pan or the oven, then molded into cups or other shapes.

Process and Low-Fat Cheeses Process cheese is an industrial version of cheese that makes use of surplus, sc.r.a.p, and unripened materials. It began as a kind of resolidified, long-keeping fondue made from tr.i.m.m.i.n.gs of genuine cheeses that were unsaleable due to partial defects or damage. The first industrial attempts to melt together a blend of shredded cheeses were made at the end of the 19th century. The key insight - the necessity of "melting salts" a.n.a.logous to the tartaric acid and citric acid in a fondue's wine or lemon juice - came in Switzerland in 1912. Five years later, the American company Kraft patented a combination of citric acid and phosphates, and a decade after that it brought out the popular cheddar look-alike Velveeta. is an industrial version of cheese that makes use of surplus, sc.r.a.p, and unripened materials. It began as a kind of resolidified, long-keeping fondue made from tr.i.m.m.i.n.gs of genuine cheeses that were unsaleable due to partial defects or damage. The first industrial attempts to melt together a blend of shredded cheeses were made at the end of the 19th century. The key insight - the necessity of "melting salts" a.n.a.logous to the tartaric acid and citric acid in a fondue's wine or lemon juice - came in Switzerland in 1912. Five years later, the American company Kraft patented a combination of citric acid and phosphates, and a decade after that it brought out the popular cheddar look-alike Velveeta.

Today, manufacturers use a mixture of sodium citrate, sodium phosphates, and sodium polyphosphates, and a blend of new, partly ripened, and fully ripened cheeses. The polyphosphates (negatively charged chains of phosphorus and oxygen atoms that attract a cloud of water molecules) not only remove calcium from the casein matrix, but also bind to the casein themselves, bringing moisture with them and thus further loosening the protein matrix. The same salts that melt the component cheeses into a h.o.m.ogeneous ma.s.s also help the resulting blended cheese melt nicely when cooked. This characteristic, together with its low cost, has made process cheese a popular ingredient in fast-food sandwiches.

Low- and no-fat "cheese products" replace fat with various carbohydrates or proteins. When heated, such products don't melt; they soften and then dry out.

Cheese and Health Cheese and the Heart As a food that is essentially a concentrated version of milk, cheese shares many of milk's nutritional advantages and disadvantages. It's a rich source of protein, calcium, and energy. Its abundant fat is highly saturated and therefore tends to raise blood cholesterol levels. However, France and Greece lead the world in per capita cheese consumption, at better than 2 oz/60 gm per day, about double the U.S. figures, yet they're remarkable among Western countries for their relatively low rates of heart disease, probably thanks to their high consumption of heart-protective vegetables, fruits, and wine (p. 253). Eating cheese as part of a balanced diet is fully compatible with good health. As a food that is essentially a concentrated version of milk, cheese shares many of milk's nutritional advantages and disadvantages. It's a rich source of protein, calcium, and energy. Its abundant fat is highly saturated and therefore tends to raise blood cholesterol levels. However, France and Greece lead the world in per capita cheese consumption, at better than 2 oz/60 gm per day, about double the U.S. figures, yet they're remarkable among Western countries for their relatively low rates of heart disease, probably thanks to their high consumption of heart-protective vegetables, fruits, and wine (p. 253). Eating cheese as part of a balanced diet is fully compatible with good health.

Food Poisoning Cheeses Made from Raw and Pasteurized Milks Government concerns about the danger of the various pathogens that can grow in milk led to the U.S. requirement (originating in 1944, reaffirmed in 1949, and extended to imports in 1951) that all cheeses aged less than 60 days be made with pasteurized milk. Since 1948 there have been only a handful of outbreaks of food poisoning in the United States caused by cheese, nearly all involving contamination of the milk or cheese after pasteurization. In Europe, where young raw-milk cheeses are still legal in some countries, most outbreaks have also been caused by pasteurized cheeses. Cheeses in general present a relatively low risk of food poisoning. Because any soft cheese contains enough moisture to permit the survival of various human pathogens, both pasteurized and unpasteurized versions are probably best avoided by people who may be especially vulnerable to infection (pregnant women, the elderly and chronically ill). Hard cheeses are inhospitable to disease microbes and very seldom cause food poisoning. Government concerns about the danger of the various pathogens that can grow in milk led to the U.S. requirement (originating in 1944, reaffirmed in 1949, and extended to imports in 1951) that all cheeses aged less than 60 days be made with pasteurized milk. Since 1948 there have been only a handful of outbreaks of food poisoning in the United States caused by cheese, nearly all involving contamination of the milk or cheese after pasteurization. In Europe, where young raw-milk cheeses are still legal in some countries, most outbreaks have also been caused by pasteurized cheeses. Cheeses in general present a relatively low risk of food poisoning. Because any soft cheese contains enough moisture to permit the survival of various human pathogens, both pasteurized and unpasteurized versions are probably best avoided by people who may be especially vulnerable to infection (pregnant women, the elderly and chronically ill). Hard cheeses are inhospitable to disease microbes and very seldom cause food poisoning.

Storage Molds In addition to the usual disease microbes, the molds that can grow on cheese are of some concern. When cheeses are held in storage for some time, toxin-producing foreign molds ( In addition to the usual disease microbes, the molds that can grow on cheese are of some concern. When cheeses are held in storage for some time, toxin-producing foreign molds (Aspergillus versicolor, Penicillium viridicatum and and P. cyclopium P. cyclopium) may occasionally develop on their rinds and contaminate them to the depth of up to an inch/2 cm. This problem appears to be very rare, but does make it advisable to discard cheeses overgrown with unusual mold.

Amines There is one normal microbial product that can cause discomfort to some people. In a strongly ripened cheese, the casein proteins are broken down to amino acids, and the amino acids can be broken down into amines, small molecules that can serve as chemical signals in the human body. Histamine and tyramine are found in large quant.i.ties in Cheddar, blue, Swiss, and Dutch-style cheeses, and can cause a rise in blood pressure, headaches, and rashes in people who are especially sensitive to them. There is one normal microbial product that can cause discomfort to some people. In a strongly ripened cheese, the casein proteins are broken down to amino acids, and the amino acids can be broken down into amines, small molecules that can serve as chemical signals in the human body. Histamine and tyramine are found in large quant.i.ties in Cheddar, blue, Swiss, and Dutch-style cheeses, and can cause a rise in blood pressure, headaches, and rashes in people who are especially sensitive to them.

Tooth Decay Finally, it has been recognized for decades that eating cheese slows tooth decay, which is caused by acid secretion from relatives of a yogurt bacterium (especially Finally, it has been recognized for decades that eating cheese slows tooth decay, which is caused by acid secretion from relatives of a yogurt bacterium (especially Streptococcus mutans Streptococcus mutans) that adhere to the teeth. Just why is still not entirely clear, but it appears that eaten at the end of a meal, when streptococcal acid production is on the rise, calcium and phosphate from the cheese diffuse into the bacterial colonies and blunt the acid rise.

Chapter 2.

Eggs

The Chicken and the Egg The Evolution of the EggThe Chicken, from Jungle to BarnyardThe Industrial Egg Egg Biology and Chemistry How the Hen Makes an EggThe YolkThe WhiteThe Nutritional Value of Eggs Egg Quality, Handling, and Safety Egg GradesDeterioration in Egg QualityHandling and Storing EggsEgg Safety: The Salmonella Problem The Chemistry of Egg Cooking: How Eggs Get Hard and Custards Thicken Protein CoagulationThe Chemistry of Egg Flavor Basic Egg Dishes Eggs Cooked In the Sh.e.l.lEggs Cooked Out of the Sh.e.l.l Egg-Liquid Mixtures: Custards and Creams DefinitionsDilution Demands DelicacyCustard Theory and PracticeCream Theory and Practice Egg Foams: Cooking with the Wrist How the Egg Proteins Stabilize FoamsHow Proteins Destabilize Destabilize Foams FoamsThe Enemies of Egg FoamsThe Effects of Other IngredientsBasic Egg-Beating TechniquesMeringues: Sweet Foams on Their OwnSouffles: A Breath of Hot AirYolk Foams: Zabaglione and Sabayons Pickled and Preserved Eggs Pickled EggsChinese Preserved Eggs The egg is one of the kitchen's marvels, and one of nature's. Its simple, placid shape houses an everyday miracle: the transformation of a bland bag of nutrients into a living, breathing, vigorous creature. The egg has loomed large as a symbol for the enigmatic origins of animals, of humans, of G.o.ds, of the earth, of the entire cosmos. The Egyptian Book of the Dead, the Indian Rg Veda, Greek Orphic mysteries, and creation myths throughout the world have been inspired by the eruption of life from within a lifeless, blank sh.e.l.l.

Humpty Dumpty has had a great fall! If eggs inspire any notable feeling today, it's boredom tinged by wariness. The chicken egg is now an industrial product, so familiar that it would be almost invisible - except that it was stigmatized by the cholesterol phobia of the 1970s and 1980s.

Neither familiarity nor fear should obscure eggs' great versatility. Their contents are primal, the unstructured stuff of life. This is why they are protean, why the cook can use them to generate such a variety of structures, from a light, insubstantial meringue to a dense, lingeringly rich custard. Eggs reconcile oil and water in a host of smooth sauces; they refine the texture of candies and ice creams; they give flavor, substance, and nutritiousness to soups, drinks, breads, pastas, and cakes; they put a s.h.i.+ne on pastries; they clarify meat stocks and wines. On their own, they're amenable to being boiled, fried, deep-fried, baked, roasted, pickled, and fermented.

Meanwhile modern science has only deepened the egg's aptness as an emblem of creation. The yolk is a stockpile of fuel obtained by the hen from seeds and leaves, which are in turn stockpiles of the sun's radiant energy. The yellow pigments that gave the yolk its name also come directly from plants, where they protect the chemical machinery of photosynthesis from being overwhelmed by the sun. So the egg does embody the chain of creation, from the developing chick back through the hen to the plants that fed her, and then to the ultimate source of life's fire, the yellow sphere of the sky. An egg is the sun's light refracted into life.

Many animals lay eggs, and humans exploit a number of them, from pigeons and turkeys to wild birds, penguins, turtles, and crocodiles. The chicken egg is by far the most commonly eaten in most countries, so I'll concentrate on it, with occasional asides on duck eggs.

The Chicken and the Egg Over the centuries there have been several clever answers to the conundrum, Which came first: the chicken or the egg? The Church Fathers sided with the chicken, pointing out that according to Genesis, G.o.d first created the creatures, not their reproductive apparatus. The Victorian Samuel Butler awarded the egg overall priority when he said that a chicken is just an egg's way of making another egg. About one point, however, there is no dispute: eggs existed long before chickens did. Ultimately, we owe our souffles and sunny-sides-up to the invention of s.e.x.

The Evolution of the Egg Sharing DNA Defined broadly, the egg is a kind of cell that is specialized for the process of s.e.xual reproduction, in which two parents contribute genes to the making of a new individual. The first living things were single cells and reproduced on their own, each cell simply making a copy of its DNA and then dividing itself into two cells. The first s.e.xual organisms, probably single-celled algae, paired up and exchanged DNA with each other before dividing - a mixing that greatly facilitated genetic change. Specialized egg and sperm cells became necessary around a billion years ago, when many-celled organisms evolved and this simple transfer of DNA was no longer possible. Defined broadly, the egg is a kind of cell that is specialized for the process of s.e.xual reproduction, in which two parents contribute genes to the making of a new individual. The first living things were single cells and reproduced on their own, each cell simply making a copy of its DNA and then dividing itself into two cells. The first s.e.xual organisms, probably single-celled algae, paired up and exchanged DNA with each other before dividing - a mixing that greatly facilitated genetic change. Specialized egg and sperm cells became necessary around a billion years ago, when many-celled organisms evolved and this simple transfer of DNA was no longer possible.

The World EggIn the beginning this world was nonexistent. It became existent. It developed. It turned into an egg. It lay for the period of a year. It split apart. One of the parts became silver, one gold.That which was silver is this earth. That which was gold is the sky. That which was the outer membrane is the mountains. That which was the inner membrane is clouds and mist. What were the veins are the rivers. What was the fluid within is the ocean.What was born from the egg is the sun. When it was born, shouts and hurrahs and all beings and all desires rose up toward it. Therefore at its rise and at its every return, shouts and hurrahs and all beings and all desires rise up toward it.- Chandogya Upanishad Chandogya Upanishad, ca. 800 BCE BCE What makes an egg an egg? Of the two reproductive cells, it's the larger, less mobile one. It receives the sperm cell, accommodates the joining of the two gene sets, and then divides and differentiates into the embryonic organism. It also provides food for at least the initial stages of this growth. This is why eggs are so nutritious: Like milk and like plant seeds, they are actually designed to be foods, to support new creatures until they are able to fend for themselves.

Improving the Package The first animal eggs were released into the equable oceans, where their outer membrane could be simple and their food supply minimal. Some 300 million years ago, the earliest fully landdwelling animals, the reptiles, developed a self-contained egg with a leathery skin that slowed fatal water loss, and with enough food to support prolonged embryonic development into a fully formed animal. The eggs of birds, animals that arose some 100 million years later, are a refined version of the primitive reptile egg. Their hard, mineralized sh.e.l.l is impermeable enough that the embryo can develop in the driest habitats; and they contain an array of antimicrobial defenses. These developments made the bird egg into an ideal human food. It contains a sizeable and balanced portion of animal nutrients; and it's so well packaged that it keeps for weeks with little or no care. The first animal eggs were released into the equable oceans, where their outer membrane could be simple and their food supply minimal. Some 300 million years ago, the earliest fully landdwelling animals, the reptiles, developed a self-contained egg with a leathery skin that slowed fatal water loss, and with enough food to support prolonged embryonic development into a fully formed animal. The eggs of birds, animals that arose some 100 million years later, are a refined version of the primitive reptile egg. Their hard, mineralized sh.e.l.l is impermeable enough that the embryo can develop in the driest habitats; and they contain an array of antimicrobial defenses. These developments made the bird egg into an ideal human food. It contains a sizeable and balanced portion of animal nutrients; and it's so well packaged that it keeps for weeks with little or no care.

The Chicken, from Jungle to Barnyard Eggs, then, are nearly a billion years older than the oldest birds. The genus Gallus, Gallus, to which the chicken belongs, is a mere 8 million years old, and to which the chicken belongs, is a mere 8 million years old, and Gallus gallus, Gallus gallus, the chicken species, has been around only for the last 3 to 4 million years. the chicken species, has been around only for the last 3 to 4 million years.

For a barnyard commoner, the chicken has a surprisingly exotic background. Its immediate ancestors were jungle fowl native to tropical and subtropical Southeast Asia and India. The chicken more or less as we know it was probably domesticated in Southeast Asia before 7500 BCE BCE, which is when larger-than-wild bones date from in Chinese finds far north of the jungle fowl's current range. By 1500 BCE BCE chickens had found their way to Sumer and Egypt, and they arrived around 800 chickens had found their way to Sumer and Egypt, and they arrived around 800 BCE BCE in Greece, where they became known as "Persian birds," and where quail were the primary source of eggs. in Greece, where they became known as "Persian birds," and where quail were the primary source of eggs.

The Domestic Egg We'll never know exactly why chickens were domesticated, but they may well have been valued more for their prolific egg production than for their meat. Some birds will lay only a set number of eggs at a time, no matter what happens to the eggs. Others, including the chicken, will lay until they acc.u.mulate a certain number in the nest. If an egg is taken by a predator, the hen will lay another to replace it - and may do so indefinitely. Over a lifetime, these "indeterminate layers" will produce many more eggs than the "determinate" layers. Wild Indian jungle fowl lay clutches of about twelve glossy, brown eggs a few times each year. In industrial production - the ecological equivalent of unlimited food resources combined with unrelenting predation - their domesticated cousins will lay an egg a day for a year or more. We'll never know exactly why chickens were domesticated, but they may well have been valued more for their prolific egg production than for their meat. Some birds will lay only a set number of eggs at a time, no matter what happens to the eggs. Others, including the chicken, will lay until they acc.u.mulate a certain number in the nest. If an egg is taken by a predator, the hen will lay another to replace it - and may do so indefinitely. Over a lifetime, these "indeterminate layers" will produce many more eggs than the "determinate" layers. Wild Indian jungle fowl lay clutches of about twelve glossy, brown eggs a few times each year. In industrial production - the ecological equivalent of unlimited food resources combined with unrelenting predation - their domesticated cousins will lay an egg a day for a year or more.

Food Words: Egg Egg and and Yolk YolkEgg comes from an Indo-European root meaning "bird." comes from an Indo-European root meaning "bird."The brusque-sounding yolk yolk is rich in overtones of light and life. It comes from the Old English for "yellow," whose Greek cousin meant "yellow-green," the color of new plant growth. Both the Old English and the Greek derive ultimately from an Indo-European root meaning "to gleam, to glimmer." The same root gave us is rich in overtones of light and life. It comes from the Old English for "yellow," whose Greek cousin meant "yellow-green," the color of new plant growth. Both the Old English and the Greek derive ultimately from an Indo-European root meaning "to gleam, to glimmer." The same root gave us glow glow and and gold. gold.

Cooked Eggs Doubtless bird eggs have been roasted ever since humans mastered fire; in Doubtless bird eggs have been roasted ever since humans mastered fire; in As You Like It As You Like It Shakespeare has Touchstone call Corin "d.a.m.ned, like an ill-roasted egg, all on one side." Salting and pickling eggs are ancient treatments that preserved the spring's bounty for use throughout the year. We know from the recipes of Apicius that the Romans ate Shakespeare has Touchstone call Corin "d.a.m.ned, like an ill-roasted egg, all on one side." Salting and pickling eggs are ancient treatments that preserved the spring's bounty for use throughout the year. We know from the recipes of Apicius that the Romans ate ova frixa, elixa, et hapala ova frixa, elixa, et hapala - fried, boiled, and "soft" eggs - and the - fried, boiled, and "soft" eggs - and the patina, patina, which could be a savory quiche or a sweet custard. By medieval times, the French were sophisticated omelet makers and the English were dressing poached eggs with the sauce that would come to be called which could be a savory quiche or a sweet custard. By medieval times, the French were sophisticated omelet makers and the English were dressing poached eggs with the sauce that would come to be called creme anglaise. creme anglaise. Savory yolk-based sauces and egg-white foams developed over the next three centuries. By around 1900, Escoffier had a repertoire of more than 300 egg dishes, and in his Savory yolk-based sauces and egg-white foams developed over the next three centuries. By around 1900, Escoffier had a repertoire of more than 300 egg dishes, and in his Gastronomie Pratique, Gastronomie Pratique, Ali Bab gave a playful recipe for a "Symphony of Eggs" - a four-egg omelet containing two chopped hard-cooked and six whole poached eggs. Ali Bab gave a playful recipe for a "Symphony of Eggs" - a four-egg omelet containing two chopped hard-cooked and six whole poached eggs.

The Industrial Egg Hen Fever The chicken underwent more evolutionary change between 1850 and 1900 than it had in its entire lifetime as a species, and under an unusual selection pressure: the fascination of Europeans and Americans with the exotic East. A political opening between England and China brought specimens of previously unknown Chinese breeds, the large, showy Cochins, to the West. These spectacular birds, so different from the run of the barnyard, touched off a chicken-breeding craze comparable to the Dutch tulip mania of the 17th century. During this "hen fever," as one observer of the American scene called it, poultry shows were very popular and hundreds of new breeds were developed. The chicken underwent more evolutionary change between 1850 and 1900 than it had in its entire lifetime as a species, and under an unusual selection pressure: the fascination of Europeans and Americans with the exotic East. A political opening between England and China brought specimens of previously unknown Chinese breeds, the large, showy Cochins, to the West. These spectacular birds, so different from the run of the barnyard, touched off a chicken-breeding craze comparable to the Dutch tulip mania of the 17th century. During this "hen fever," as one observer of the American scene called it, poultry shows were very popular and hundreds of new breeds were developed.

Roman Custards, Savory and SweetPatina of SolesBeat and clean the soles and put in patina [a shallow pan]. Throw in oil, liquamen [fish sauce], wine. While the dish cooks, pound and rub pepper, lovage, oregano; pour in some of the cooking liquid, add raw eggs, and make into one ma.s.s. Pour over the soles and cook on a slow fire. When the dish has come together, sprinkle with pepper and serve."Cheese" PatinaMeasure out enough milk for your pan, mix with honey as for other milk dishes, add five eggs for [a pint], three for [a half-pint]. Mix them in the milk until they make one ma.s.s, strain into a dish from c.u.ma, and cook over a slow fire. When it is ready, sprinkle with pepper and serve.- from Apicius, first few centuries CE CE Ordinary farm stock was also improved. Just a few decades after its arrival in the United States from Tuscany around 1830, descendents of the White Leghorn emerged as the champion layers. Versions of the Cornish, itself the offshoot of Asiatic fighting breeds, were deemed the best meat birds; and the Plymouth Rock and Rhode Island Red, whose eggs are brown, were bred as dual-purpose chickens. As interest in the show birds faded, the egg and meat breeds became ever more dominant. Today, an egg or meat chicken is usually the product of four purebred grandparents. Nearly all of the diversity generated in the 1800s has disappeared. Among industrialized countries, only France and Australia have remained independent of the handful of multinational corporations that provide laying stock to the egg industry.

Ma.s.s Production The 20th century saw the general farm lose its poultry shed to the poultry farm or ranch, which has in turn been split up into separate hatcheries and meat and egg factories. Economies of scale dictate that production units be as large as possible - one caretaker can manage a flock of 100,000, and many ranches now have a million or more laying hens. Today's typical layer is born in an incubator, eats a diet that originates largely in the laboratory, lives and lays on wire and under lights for about a year, and produces between 250 and 290 eggs. As Page Smith and Charles Daniel put it in their The 20th century saw the general farm lose its poultry shed to the poultry farm or ranch, which has in turn been split up into separate hatcheries and meat and egg factories. Economies of scale dictate that production units be as large as possible - one caretaker can manage a flock of 100,000, and many ranches now have a million or more laying hens. Today's typical layer is born in an incubator, eats a diet that originates largely in the laboratory, lives and lays on wire and under lights for about a year, and produces between 250 and 290 eggs. As Page Smith and Charles Daniel put it in their Chicken Book, Chicken Book, the chicken is no longer "a lively creature but merely an element in an industrial process whose product [is] the egg." the chicken is no longer "a lively creature but merely an element in an industrial process whose product [is] the egg."

A Medieval Omelet and English CreamArboulastre (An Omelet) (An Omelet)[First prepare mixed herbs, including rue, tansy, mint, sage, marjoram, fennel, parsley, violet leaves, spinach, lettuce, clary, ginger.] Then have seven eggs well beaten together, yolks and whites, and mix with the herbs. Then divide in two and make two allumelles, allumelles, which are fried in the following manner. First you heat your frying pan well with oil, b.u.t.ter, or whatever fat you like. When it is well heated, especially toward the handle, mix and cast your eggs upon the pan, and turn frequently with a paddle over and under; then throw some good grated cheese on top. Know that it is done thus because if you mix the cheese with the eggs and herbs, when you fry the which are fried in the following manner. First you heat your frying pan well with oil, b.u.t.ter, or whatever fat you like. When it is well heated, especially toward the handle, mix and cast your eggs upon the pan, and turn frequently with a paddle over and under; then throw some good grated cheese on top. Know that it is done thus because if you mix the cheese with the eggs and herbs, when you fry the allumelle, allumelle, the cheese that is underneath sticks to the pan.... And when your herbs are fried in the pan, shape your the cheese that is underneath sticks to the pan.... And when your herbs are fried in the pan, shape your arboulastre arboulastre into a square or round form, and eat it neither too hot nor too cold. into a square or round form, and eat it neither too hot nor too cold.- Le Menagier de Paris Le Menagier de Paris, ca. 1390Poche to Potage (Poached Eggs in Creme Anglaise)Take eggs and break them into boiling water, and let them seethe, and when they are done take them out, and take milk and yolks of eggs, and beat them well together, and put them in a pot; and add sugar or honey, and color it with saffron, and let it seethe; and at the first boil take it off, and cast therein powder of ginger, and dress the cooked eggs in dishes, and pour the pottage above, and serve it forth.- from a ma.n.u.script published in Antiquitates Culinariae, Antiquitates Culinariae, 1791 (ca. 1400) 1791 (ca. 1400) Benefits and Costs The industrialization of the chicken has brought benefits, and these shouldn't be underestimated. A pound of broiler can now be produced from less than two pounds of feed, a pound of eggs from less than three, so both chickens and eggs are bargains among animal foods. Egg quality has also improved. City and country dwellers alike enjoy fresher, more uniform eggs than formerly, when small-farm hens ran free and laid in odd places, and when spring eggs were stored until winter in limewater or watergla.s.s (see p. 115). Refrigeration alone has made a tremendous difference. Year-round laying (made possible by controlled lighting and temperature), prompt gathering and cooling, and daily s.h.i.+pping by rapid, refrigerated transport mean that good eggs deteriorate much less between hen and cook than they did in the more relaxed, more humane past. The industrialization of the chicken has brought benefits, and these shouldn't be underestimated. A pound of broiler can now be produced from less than two pounds of feed, a pound of eggs from less than three, so both chickens and eggs are bargains among animal foods. Egg quality has also improved. City and country dwellers alike enjoy fresher, more uniform eggs than formerly, when small-farm hens ran free and laid in odd places, and when spring eggs were stored until winter in limewater or watergla.s.s (see p. 115). Refrigeration alone has made a tremendous difference. Year-round laying (made possible by controlled lighting and temperature), prompt gathering and cooling, and daily s.h.i.+pping by rapid, refrigerated transport mean that good eggs deteriorate much less between hen and cook than they did in the more relaxed, more humane past.

There are drawbacks to the industrial egg. While average quality has improved, people who pay close attention to eggs say that flavor has suffered: that the chicken's natural, varied diet of grains, leaves, and bugs provides a richness that the commercial soy and fish meals don't. (This difference has proven hard to doc.u.ment in taste tests; see p. 87.) In addition, ma.s.s husbandry has played a role in the rising incidence of salmonella contamination. "Spent" hens are often recycled into feed for the next generation of layers, so that salmonella infection is readily spread by careless processing. Finally, there is a more difficult question: whether we can enjoy good, cheap eggs more humanely, without reducing descendents of the spirited jungle fowl to biological machines that never see the sun, scratch in the dust, or have more than an inch or two to move.

Freer Range? Enough people have become uncomfortable with the excesses of industrialization, and willing to pay a substantial premium for their eggs, that smaller-scale, "free-range" and "organically fed" laying flocks have made a comeback in the United States and Europe. Swiss law now requires that all hens in that country have free access to the outdoors. The term "free-range" can be misleading; it sometimes means only that the chickens live in a slightly larger cage than usual, or have brief access to the outdoors. Still, with people eating fewer eggs in the home, spending so little on those eggs, and paying more attention to what they eat, the odds are good that this modest de-industrialization of the egg will continue. Enough people have become uncomfortable with the excesses of industrialization, and willing to pay a substantial premium for their eggs, that smaller-scale, "free-range" and "organically fed" laying flocks have made a comeback in the United States and Europe. Swiss law now requires that all hens in that country have free access to the outdoors. The term "free-range" can be misleading; it sometimes means only that the chickens live in a slightly larger cage than usual, or have brief access to the outdoors. Still, with people eating fewer eggs in the home, spending so little on those eggs, and paying more attention to what they eat, the odds are good that this modest de-industrialization of the egg will continue.

Egg Biology and Chemistry How the Hen Makes an Egg The egg is so familiar that we seldom remember to marvel at its making. All animals work hard at the business of reproduction, but the hen does more than most. Her "reproductive effort," defined as the fraction of body weight that an animal deposits daily in her potential offspring, is 100 times greater than a human's. Each egg is about 3% of the hen's weight, so in a year of laying, she converts about eight times her body weight into eggs. A quarter of her daily energy expenditure goes toward egg-making; a duck puts in half.

The chicken egg begins with the pinhead-sized white disc that we see riding atop the yellow yolk. This is the business end of the egg, the living germ cell that contains the hen's chromosomes. A hen is born with several thousand microscopic germ cells in her single ovary.

Making the Yolk As the hen grows, her germ cells gradually reach a few millimeters in diameter, and after two or three months acc.u.mulate a white, primordial form of yolk inside their thin surrounding membrane. (The white yolk can be seen in a hard-cooked egg; see box, p. 74.) When the hen reaches laying age at between four and six months, the egg cells begin to mature, with different cells at different stages at any given time. Full maturation takes about ten weeks. During the tenth, the germ cell rapidly acc.u.mulates yellow yolk, mostly fats and proteins, which is synthesized in the hen's liver. Its color depends on the pigments in the hen's feed; a diet rich in corn or alfalfa makes a deeper yellow. If the hen feeds only once or twice a day, her yolk will show distinct layers of dark and light. In the end, the yolk comes to dwarf the germ cell, containing as it must the provisions for 21 days during which the chick will develop on its own. As the hen grows, her germ cells gradually reach a few millimeters in diameter, and after two or three months acc.u.mulate a white, primordial form of yolk inside their thin surrounding membrane. (The white yolk can be seen in a hard-cooked egg; see box, p. 74.) When the hen reaches laying age at between four and six months, the egg cells begin to mature, with different cells at different stages at any given time. Full maturation takes about ten weeks. During the tenth, the germ cell rapidly acc.u.mulates yellow yolk, mostly fats and proteins, which is synthesized in the hen's liver. Its color depends on the pigments in the hen's feed; a diet rich in corn or alfalfa makes a deeper yellow. If the hen feeds only once or twice a day, her yolk will show distinct layers of dark and light. In the end, the yolk comes to dwarf the germ cell, containing as it must the provisions for 21 days during which the chick will develop on its own.

Making the White The rest of the egg provides both nourishment and protective housing for the germ cell. Its construction takes about 25 hours and begins when the ovary releases the completed yolk. The yolk is then gripped by the funnel-shaped opening of the oviduct, a tube 23 feet/0.60.9 meter long. If the hen has mated in recent days, there will be sperm stored in a "nest" at the upper end of the oviduct, and one will fuse with the egg cell. Fertilized or not - and most eggs are not - the yolk spends two to three hours slowly pa.s.sing down the upper end of the oviduct. Protein-secreting cells in the oviduct lining add a thickening layer to its membrane, and then coat it with about half the final volume of the egg white, or The rest of the egg provides both nourishment and protective housing for the germ cell. Its construction takes about 25 hours and begins when the ovary releases the completed yolk. The yolk is then gripped by the funnel-shaped opening of the oviduct, a tube 23 feet/0.60.9 meter long. If the hen has mated in recent days, there will be sperm stored in a "nest" at the upper end of the oviduct, and one will fuse with the egg cell. Fertilized or not - and most eggs are not - the yolk spends two to three hours slowly pa.s.sing down the upper end of the oviduct. Protein-secreting cells in the oviduct lining add a thickening layer to its membrane, and then coat it with about half the final volume of the egg white, or alb.u.men alb.u.men (from the Latin (from the Latin albus, albus, meaning "white"). They apply this portion of alb.u.men in four layers that are alternately thick and thin in consistency. meaning "white"). They apply this portion of alb.u.men in four layers that are alternately thick and thin in consistency.

The first thick layer of alb.u.men protein is twisted by spiraling grooves in the oviduct wall to form the chalazae chalazae (from the Greek for "small lump," "hailstone"), two dense, slightly elastic cords which anchor the yolk to the ends of the sh.e.l.l and allow it to rotate while suspending it in the middle of the egg. This system keeps as much cus.h.i.+oning alb.u.men as possible between the embryo and the sh.e.l.l, and prevents premature contact between sh.e.l.l and embryo, which could distort the embryo's development. (from the Greek for "small lump," "hailstone"), two dense, slightly elastic cords which anchor the yolk to the ends of the sh.e.l.l and allow it to rotate while suspending it in the middle of the egg. This system keeps as much cus.h.i.+oning alb.u.men as possible between the embryo and the sh.e.l.l, and prevents premature contact between sh.e.l.l and embryo, which could distort the embryo's development.

Membranes, Water, and Sh.e.l.l Once the alb.u.men proteins have been applied to the yolk, it spends an hour in the next section of the oviduct being loosely enclosed in two tough, antimicrobial protein membranes that are attached to each other everywhere except for one end, where the air pocket will later develop to supply the hatching chick with its first gulps of air. Then comes a long stretch - 19 or 20 hours - in the 2-inch-/5-cm-long uterus, or sh.e.l.l gland. For five hours, cells in the uterus wall pump water and salts through the membranes and into the alb.u.men and "plump" the egg to its full volume. When the membranes are taut, the uterine lining secretes calcium carbonate and protein to form the sh.e.l.l, a process that takes about 14 hours. Since the embryo needs air, the sh.e.l.l is riddled (especially at the blunt end) with some 10,000 pores that add up to a hole about 2 mm in diameter. Once the alb.u.men proteins have been applied to the yolk, it spends an hour in the next section of the oviduct being loosely enclosed in two tough, antimicrobial protein membranes that are attached to each other everywhere except for one end, where the air pocket will later develop to supply the hatching chick with its first gulps of air. Then comes a long stretch - 19 or 20 hours - in the 2-inch-/5-cm-long uterus, or sh.e.l.l gland. For five hours, cells in the uterus wall pump water and salts through the membranes and into the alb.u.men and "plump" the egg to its full volume. When the membranes are taut, the uterine lining secretes calcium carbonate and protein to form the sh.e.l.l, a process that takes about 14 hours. Since the embryo needs air, the sh.e.l.l is riddled (especially at the blunt end) with some 10,000 pores that add up to a hole about 2 mm in diameter.

Germ-Side Up: Primordial YolkHave you ever noticed that when you crack open a raw egg, the germ cell - the pinhead-sized white disc that carries the hen's DNA - usually comes to the top of the yolk? It does so because the channel of primordial white yolk below it is less dense than the yellow yolk - so the egg cell's side of the yolk is lighter, and rises. In the intact egg, the chalazae allow the germ cell to return to the top whenever the hen rearranges her eggs.That persistent bit of uncoagulated yolk at the center of a hard-cooked egg is primordial white yolk, especially rich in iron, which the hen deposits in its eggs when they're barely a quarter-inch/6 mm in diameter.

Cuticle and Color The hen's finis.h.i.+ng touch on her egg is a thin proteinaceous cuticle. This coating initially plugs up the pores to slow water loss and block the entry of bacteria, but gradually fractures to allow the chick to get enough oxygen. Along with the cuticle comes color, in the form of chemical relatives of hemoglobin. Egg color is determined by the hen's genetic background, and has no relation to the egg's taste or nutritional value. Leghorns lay very lightly pigmented "white" eggs. Brown eggs are produced by breeds that were originally dual-purpose egg and meat birds, including Rhode Island Reds and Plymouth Rocks; New Hamps.h.i.+re and Australorps hens were bred for intensive brown-egg production. Chinese Cochin hens paint their eggs with fine yellow dots. Thanks to a dominant trait unknown in any other wild or domestic chickens, the rare Chilean Araucana lays blue eggs. Crosses between Araucanas and brown-egg breeds make both blue and brown pigments and thus green sh.e.l.ls. The hen's finis.h.i.+ng touch on her egg is a thin proteinaceous cuticle. This coating initially plugs up the pores to slow water loss and block the entry of bacteria, but gradually fractures to allow the chick to get enough oxygen. Along with the cuticle comes color, in the form of chemical relatives of hemoglobin. Egg color is determined by the hen's genetic background, and has no relation to the egg's taste or nutritional value. Leghorns lay very lightly pigmented "white" eggs. Brown eggs are produced by breeds that were originally dual-purpose egg and meat birds, including Rhode Island Reds and Plymouth Rocks; New Hamps.h.i.+re and Australorps hens were bred for intensive brown-egg production. Chinese Cochin hens paint their eggs with fine yellow dots. Thanks to a dominant trait unknown in any other wild or domestic chickens, the rare Chilean Araucana lays blue eggs. Crosses between Araucanas and brown-egg breeds make both blue and brown pigments and thus green sh.e.l.ls.

The completed egg is expelled blunt end first about 25 hours after leaving the ovary. As the egg cools down from the hen's high body temperature (106F/41C), its contents shrink slightly. This contraction pulls the inner sh.e.l.l membrane away from its outer partner at the blunt end and thereby forms the air s.p.a.ce, whose size is an indicator of egg freshness (p. 81).

The Yolk The yolk accounts for just over a third of a sh.e.l.led egg's weight, and its biological purpose is almost exclusively nutritive. It carries three-quarters of the calories and most of the iron, thiamin, and vitamin A of the egg as a whole. The yolk's yellow color comes not from the vitamin-A precursor beta-carotene, the orange pigment in carrots and other plant foods, but from plant pigments called xanthophylls (p. 267), which the hen obtains mainly from alfalfa and corn feeds. Producers may supplement the feeds with marigold petals and