Characteristics Characteristics

Yogurt

Tart, semisolid, smooth; green aroma Tart, semisolid, smooth; green aroma

b.u.t.termilk

Tart, thickened liquid; b.u.t.tery aroma Tart, thickened liquid; b.u.t.tery aroma

Creme fraiche

Mildly tart and thickened; b.u.t.tery aroma Mildly tart and thickened; b.u.t.tery aroma

Sour cream

Mildly tart, semisolid; b.u.t.tery aroma Mildly tart, semisolid; b.u.t.tery aroma

Ropy milks

Mildly tart, semisolid, slimy; b.u.t.tery aroma Mildly tart, semisolid, slimy; b.u.t.tery aroma

Koumiss

Mildly tart, thickened liquid; effervescent, 0.72.5% alcohol Mildly tart, thickened liquid; effervescent, 0.72.5% alcohol

Kefir

Tart, thickened liquid; effervescent, 0.1% alcohol Tart, thickened liquid; effervescent, 0.1% alcohol

Sour cream, creme fraiche, and b.u.t.termilk are indigenous to relatively cool western and northern Europe, where milk spoils more slowly and was often left overnight to separate into cream for b.u.t.termaking. The lactococci and are indigenous to relatively cool western and northern Europe, where milk spoils more slowly and was often left overnight to separate into cream for b.u.t.termaking. The lactococci and Leuconostoc Leuconostoc species that produce them are "mesophilic," or moderate-temperature lovers that probably first got into milk from particles of pasturage on the cows' udders. They prefer temperatures around 85F/30C but will work well below that range, and develop moderate levels of lactic acid during a slow fermentation lasting 12 to 24 hours. species that produce them are "mesophilic," or moderate-temperature lovers that probably first got into milk from particles of pasturage on the cows' udders. They prefer temperatures around 85F/30C but will work well below that range, and develop moderate levels of lactic acid during a slow fermentation lasting 12 to 24 hours.

Yogurt Yogurt is the Turkish word for milk that has been fermented into a tart, semisolid ma.s.s; it comes from a root meaning "thick." Essentially the same product has been made for millennia from eastern Europe and North Africa across central Asia to India, where it goes by a variety of names and is used for a variety of purposes: it's eaten on its own, diluted into drinks, mixed into dressings, and used as an ingredient in soups, baked goods, and sweets. is the Turkish word for milk that has been fermented into a tart, semisolid ma.s.s; it comes from a root meaning "thick." Essentially the same product has been made for millennia from eastern Europe and North Africa across central Asia to India, where it goes by a variety of names and is used for a variety of purposes: it's eaten on its own, diluted into drinks, mixed into dressings, and used as an ingredient in soups, baked goods, and sweets.

The Health Benefits of Fermented MilksThe bacteria in dairy products may do more for us than just predigest lactose and create flavor. Recent research findings lend some support to the ancient and widespread belief that yogurt and other cultured milks can actively promote good health. Early in the 20th century, the Russian n.o.belist Ilya Metchnikov (who discovered that white blood cells fight bacterial infection) gave a scientific rationale to this belief, when he proposed that the lactic acid bacteria in fermented milks eliminate toxic microbes in our digestive system that otherwise shorten our lives. Hence Dr. James Empringham's charming t.i.tle of 1926: Intestinal Gardening for the Prolongation of Youth. Intestinal Gardening for the Prolongation of Youth.Metchnikov was prescient. Research over the last couple of decades has established that certain lactic acid bacteria, the Bifidobacteria, are fostered by breast milk, do colonize the infant intestine, and help keep it healthy by acidifying it and by producing various antibacterial substances. Once we're weaned onto a mixed diet, the Bifidobacterial majority in the intestine recedes in favor of a mixed population of Streptococcus, Staphylococcus, E. coli, Streptococcus, Staphylococcus, E. coli, and yeasts. The standard industrial yogurt and b.u.t.termilk bacteria are specialized to grow well in milk and can't survive inside the human body. But other bacteria found in traditional, spontaneously fermented milks - and yeasts. The standard industrial yogurt and b.u.t.termilk bacteria are specialized to grow well in milk and can't survive inside the human body. But other bacteria found in traditional, spontaneously fermented milks - Lactobacillus fermentum, L. casei, Lactobacillus fermentum, L. casei, and and L. brevis, L. brevis, for example - as well as for example - as well as L. plantarum L. plantarum from pickled vegetables, and the intestinal native from pickled vegetables, and the intestinal native L. acidophilus, L. acidophilus, do take up residence in us. Particular strains of these bacteria variously adhere to and shield the intestinal wall, secrete antibacterial compounds, boost the body's immune response to particular disease microbes, dismantle cholesterol and cholesterol-consuming bile acids, and reduce the production of potential carcinogens. do take up residence in us. Particular strains of these bacteria variously adhere to and shield the intestinal wall, secrete antibacterial compounds, boost the body's immune response to particular disease microbes, dismantle cholesterol and cholesterol-consuming bile acids, and reduce the production of potential carcinogens.These activities may not amount to prolonging our youth, but they're certainly desirable! Increasingly, manufacturers are adding "probiotic" Lactobacilli and even Bifidobacteria to their cultured milk products, and note that fact on the label. Such products, approximations of the original fermented milks that contained an even more diverse bacterial flora, allow us to plant our inner gardens with the most companionable microbes we're currently aware of.

Yogurt remained an exotic curiosity in Europe until early in the 20th century, when the n.o.bel Prizewinning immunologist Ilya Metchnikov connected the longevity of certain groups in Bulgaria, Russia, France, and the United States with their consumption of fermented milks, which he theorized would acidify the digestive tract and prevent pathogenic bacteria from growing (see box, p. 47). Factory-scale production and milder yogurts flavored with fruit were developed in the late 1920s, and broader popularity came in the 1960s with Swiss improvements in the inclusion of flavors and fruits and the French development of a stable, creamy stirred version.

The Yogurt Symbiosis By contrast to the complex and variable flora of traditional yogurts, the industrial version is reduced to the essentials. Standard yogurt contains just two kinds of bacteria, By contrast to the complex and variable flora of traditional yogurts, the industrial version is reduced to the essentials. Standard yogurt contains just two kinds of bacteria, Lactobacillus delbrueckii Lactobacillus delbrueckii subspecies subspecies bulgaricus, bulgaricus, and and Streptococcus salivarius Streptococcus salivarius subspecies subspecies thermophilus. thermophilus. Each bacterium stimulates the growth of the other, and the combination acidifies the milk more rapidly than either partner on its own. Initially the streptococci are most active. Then as the acidity exceeds 0.5%, the acid-sensitive streptococci slow down, and the hardier lactobacilli take over and bring the final acidity to 1% or more. The flavor compounds produced by the bacteria are dominated by acetaldehyde, which provides the characteristic refreshing impression of green apples. Each bacterium stimulates the growth of the other, and the combination acidifies the milk more rapidly than either partner on its own. Initially the streptococci are most active. Then as the acidity exceeds 0.5%, the acid-sensitive streptococci slow down, and the hardier lactobacilli take over and bring the final acidity to 1% or more. The flavor compounds produced by the bacteria are dominated by acetaldehyde, which provides the characteristic refreshing impression of green apples.

Making Yogurt There are two basic stages in yogurt making: preparing the milk by heating and partly cooling it; and fermenting the warm milk. There are two basic stages in yogurt making: preparing the milk by heating and partly cooling it; and fermenting the warm milk.

The Milk Yogurt is made from all sorts of milk; sheep and goat were probably the first. Reduced-fat milks make especially firm yogurt because manufacturers mask their lack of fat by adding extra milk proteins, which add density to the acid-coagulated protein network. (Manufacturers may also add gelatin, starch, and other stabilizers to help prevent separation of whey and curd from physical shocks during transportation and handling.) Yogurt is made from all sorts of milk; sheep and goat were probably the first. Reduced-fat milks make especially firm yogurt because manufacturers mask their lack of fat by adding extra milk proteins, which add density to the acid-coagulated protein network. (Manufacturers may also add gelatin, starch, and other stabilizers to help prevent separation of whey and curd from physical shocks during transportation and handling.) Heating the Milk Traditionally the milk for yogurt was given a prolonged boiling to concentrate the proteins and give a firmer texture. Today, manufacturers can boost protein content by adding dry milk powder, but they still cook the milk, for 30 minutes at 185F/85C or at 195F/90C for 10 minutes. These treatments improve the consistency of the yogurt by denaturing the whey protein lactoglobulin, whose otherwise unreactive molecules then partic.i.p.ate by cl.u.s.tering on the surfaces of the casein particles (p. 20). With the helpful interference of the lactoglobulins, the casein particles can only bond to each other at a few spots, and so gather not in cl.u.s.ters but in a fine matrix of chains that is much better at retaining liquid in its small interstices. Traditionally the milk for yogurt was given a prolonged boiling to concentrate the proteins and give a firmer texture. Today, manufacturers can boost protein content by adding dry milk powder, but they still cook the milk, for 30 minutes at 185F/85C or at 195F/90C for 10 minutes. These treatments improve the consistency of the yogurt by denaturing the whey protein lactoglobulin, whose otherwise unreactive molecules then partic.i.p.ate by cl.u.s.tering on the surfaces of the casein particles (p. 20). With the helpful interference of the lactoglobulins, the casein particles can only bond to each other at a few spots, and so gather not in cl.u.s.ters but in a fine matrix of chains that is much better at retaining liquid in its small interstices.

The Fermentation Once the milk has been heated, it's cooled down to the desired fermentation temperature, the bacteria are added (often in a portion of the previous batch), and the milk kept warm until it sets. The fermentation temperature has a strong influence on yogurt consistency. At the maximum temperature well tolerated by the bacteria, 104113F/4045C, the bacteria grow and produce lactic acid rapidly, and the milk proteins gel in just two or three hours; at 86F/30C, the bacteria work far more slowly, and the milk takes up to 18 hours to set. Rapid gelling produces a relatively coa.r.s.e protein network whose few thick strands give it firmness but also readily leak whey; slow gelling produces a finer, more delicate, more intricately branched network whose individual strands are weaker but whose smaller pores are better at retaining the whey. Once the milk has been heated, it's cooled down to the desired fermentation temperature, the bacteria are added (often in a portion of the previous batch), and the milk kept warm until it sets. The fermentation temperature has a strong influence on yogurt consistency. At the maximum temperature well tolerated by the bacteria, 104113F/4045C, the bacteria grow and produce lactic acid rapidly, and the milk proteins gel in just two or three hours; at 86F/30C, the bacteria work far more slowly, and the milk takes up to 18 hours to set. Rapid gelling produces a relatively coa.r.s.e protein network whose few thick strands give it firmness but also readily leak whey; slow gelling produces a finer, more delicate, more intricately branched network whose individual strands are weaker but whose smaller pores are better at retaining the whey.

Frozen Yogurt Frozen yogurt became popular in the 1970s and '80s as a low-fat, "healthy" alternative to ice cream. In fact, frozen yogurt is essentially ice milk whose mix includes a small dose of yogurt; the standard proportion is 4 to 1. Depending on the mixing procedure, the yogurt bacteria may survive in large numbers or be largely eliminated. Frozen yogurt became popular in the 1970s and '80s as a low-fat, "healthy" alternative to ice cream. In fact, frozen yogurt is essentially ice milk whose mix includes a small dose of yogurt; the standard proportion is 4 to 1. Depending on the mixing procedure, the yogurt bacteria may survive in large numbers or be largely eliminated.

Soured Creams and b.u.t.termilk, Including Creme Fraiche Before the advent of the centrifugal separator, b.u.t.ter was made in western Europe by allowing raw milk to stand overnight or longer, skimming off the cream that rose to the top, and churning the cream. During the hours of gravity separation, bacteria would grow spontaneously in the milk and give the cream and the b.u.t.ter made from it a characteristic aroma and tartness.

"Cream cultures" is a convenient shorthand for products that are now intentionally seeded with these same bacteria, which are various species of Lactococcus Lactococcus and and Leuconostoc, Leuconostoc, and have three important characteristics. They grow best at moderate temperatures, well below the typical temperature of yogurt fermentation; they're only moderate acid-producers, so the milks and creams they ferment never get extremely sour; and certain strains have the ability to convert a minor milk component, citrate, into a warmly aromatic compound called diacetyl that miraculously complements the flavor of b.u.t.terfat. It's fascinating that this single bacterial product is so closely a.s.sociated with the flavor of b.u.t.ter that all by itself, diacetyl makes foods taste b.u.t.tery: even chardonnay wines (p. 730). To accentuate this flavor note, manufacturers sometimes add citrate to the milk or cream before fermentation, and they ferment in the cool conditions that favor diacetyl production. and have three important characteristics. They grow best at moderate temperatures, well below the typical temperature of yogurt fermentation; they're only moderate acid-producers, so the milks and creams they ferment never get extremely sour; and certain strains have the ability to convert a minor milk component, citrate, into a warmly aromatic compound called diacetyl that miraculously complements the flavor of b.u.t.terfat. It's fascinating that this single bacterial product is so closely a.s.sociated with the flavor of b.u.t.ter that all by itself, diacetyl makes foods taste b.u.t.tery: even chardonnay wines (p. 730). To accentuate this flavor note, manufacturers sometimes add citrate to the milk or cream before fermentation, and they ferment in the cool conditions that favor diacetyl production.

Creme Fraiche Creme fraiche is a versatile preparation. Thick, tart, and with an aroma that can be delicately nutty or b.u.t.tery, it is a wonderful complement to fresh fruit, to caviar, and to certain pastries. And thanks to its high fat and correspondingly low protein content, it can be cooked in a sauce or even boiled down without curdling. Creme fraiche is a versatile preparation. Thick, tart, and with an aroma that can be delicately nutty or b.u.t.tery, it is a wonderful complement to fresh fruit, to caviar, and to certain pastries. And thanks to its high fat and correspondingly low protein content, it can be cooked in a sauce or even boiled down without curdling.

In France today, creme fraiche means cream with 30% fat that has been pasteurized at moderate temperatures, not UHT pasteurized (p. 22) or sterilized. (Fraiche means "cool" or "fresh.") It may, however, be either liquid ( means "cool" or "fresh.") It may, however, be either liquid (liquide, fleurette) or thick (epaisse). The liquid version is unfermented and has an official refrigerated shelf life of 15 days. The thick version is fermented with the typical cream culture for 15 to 20 hours, and has a shelf life of 30 days. As with all fermented milks, the thickening is an indication that the product has reached a certain acidity (0.8%, pH 4.6) and so a distinct tartness. Commercial American creme fraiche is made essentially as the French fermented version is, though some manufacturers add a small amount of rennet for a thicker consistency. A distinctly b.u.t.tery flavor is found in products made with Jersey and Guernsey milks (rich in citrate) and with diacetyl-producing strains of bacteria.

Making Creme Fraiche in the Kitchen A home version of creme fraiche can be made by adding some cultured b.u.t.termilk or sour cream, which contain cream-culture bacteria, to heavy cream (1 tablespoon per cup/15 ml per 250 ml), and letting it stand at a cool room temperature for 12 to 18 hours or until thick. A home version of creme fraiche can be made by adding some cultured b.u.t.termilk or sour cream, which contain cream-culture bacteria, to heavy cream (1 tablespoon per cup/15 ml per 250 ml), and letting it stand at a cool room temperature for 12 to 18 hours or until thick.

Sour Cream Sour cream is essentially a leaner, firmer, less versatile version of creme fraiche. At around 20% milk fat, it contains enough protein that cooking temperatures will curdle it. Unless it is used to enrich a dish just before serving, then, it will give a slightly grainy appearance and texture. Sour cream is especially prominent in central and eastern Europe, where it has traditionally been added to soups and stews (goulash, borscht). Immigrants brought a taste for it to American cities in the 19th century, and by the middle of the 20th it had become fully naturalized as a base for dips and salad dressings, a topping for baked potatoes, and an ingredient in cakes. American sour cream is heavier-bodied than the European original thanks to the practice of pa.s.sing the cream through a h.o.m.ogenizer twice before culturing it. A small dose of rennet is sometimes added with the bacteria; this enzyme causes the casein proteins to coagulate into a firmer gel. Sour cream is essentially a leaner, firmer, less versatile version of creme fraiche. At around 20% milk fat, it contains enough protein that cooking temperatures will curdle it. Unless it is used to enrich a dish just before serving, then, it will give a slightly grainy appearance and texture. Sour cream is especially prominent in central and eastern Europe, where it has traditionally been added to soups and stews (goulash, borscht). Immigrants brought a taste for it to American cities in the 19th century, and by the middle of the 20th it had become fully naturalized as a base for dips and salad dressings, a topping for baked potatoes, and an ingredient in cakes. American sour cream is heavier-bodied than the European original thanks to the practice of pa.s.sing the cream through a h.o.m.ogenizer twice before culturing it. A small dose of rennet is sometimes added with the bacteria; this enzyme causes the casein proteins to coagulate into a firmer gel.

A nonfermented imitation called "acidified sour cream" is made by coagulating the cream with pure acid. "Sour creams" labeled "low-fat" and "nonfat" replace b.u.t.terfat with starch, plant gums, and dried milk protein.

b.u.t.termilk Most "b.u.t.termilk" sold in the United States is not b.u.t.termilk at all. True b.u.t.termilk is the low-fat portion of milk or cream remaining after it has been churned to make b.u.t.ter. Traditionally, that milk or cream would have begun to ferment before churning, and afterwards the b.u.t.termilk would continue to thicken and develop flavor. With the advent of centrifugal cream separators in the 19th century, b.u.t.termaking produced "sweet" unfermented b.u.t.termilk, which could be sold as such or cultured with lactic bacteria to develop the traditional flavor and consistency. In the United States, a shortage of true b.u.t.termilk shortly after World War II led to the success of an imitation, "cultured b.u.t.termilk," made from ordinary skim milk and fermented until acid and thick. Most "b.u.t.termilk" sold in the United States is not b.u.t.termilk at all. True b.u.t.termilk is the low-fat portion of milk or cream remaining after it has been churned to make b.u.t.ter. Traditionally, that milk or cream would have begun to ferment before churning, and afterwards the b.u.t.termilk would continue to thicken and develop flavor. With the advent of centrifugal cream separators in the 19th century, b.u.t.termaking produced "sweet" unfermented b.u.t.termilk, which could be sold as such or cultured with lactic bacteria to develop the traditional flavor and consistency. In the United States, a shortage of true b.u.t.termilk shortly after World War II led to the success of an imitation, "cultured b.u.t.termilk," made from ordinary skim milk and fermented until acid and thick.

What's the difference? True b.u.t.termilk is less acid, subtler and more complex in flavor, and more p.r.o.ne to off-flavors and spoilage. Its remnants of fat globule membranes are rich in emulsifiers like lecithin, and make it especially valuable for preparing smooth, fine-textured foods of all kinds, from ice cream to baked goods. (Its excellence for emulsifying led to the Pennsylvania Dutch using it as a base for red barn paint!) Cultured b.u.t.termilk is useful too; it imparts a rich, tangy flavor and tenderness to griddle cakes and many baked goods.

U.S. "cultured b.u.t.termilk" is made by giving skim or low-fat milk the standard yogurt heat treatment to produce a finer protein gel, then cooling it and fermenting it with cream cultures until it gels. The gelled milk is cooled to stop the fermentation and gently agitated to break the curd into a thick but smooth liquid. "Bulgarian b.u.t.termilk" is a version of cultured b.u.t.termilk in which the cream cultures are supplemented or replaced by yogurt cultures, and fermented at a higher temperature to a higher acidity. It's noticeably more tart and gelatinous, with the apple-like sharpness typical of yogurt.

Ropy Scandinavian MilksA distinctive subfamily among the cream cultures are the "ropy" milks of Scandinavia, so-called because they're more than stringy: lift a spoonful of Finnish viili, viili, Swedish Swedish lngfil, lngfil, or Norwegian or Norwegian tattemjolk, tattemjolk, and the rest of the bowl follows it into the air. Some ropy milks are so cohesive that they're cut with a knife. This consistency is created by particular strains of cream culture bacteria that produce long strands of starch-like carbohydrate. The stretchy carbohydrate absorbs water and sticks to casein particles, so manufacturers are using ropy strains of and the rest of the bowl follows it into the air. Some ropy milks are so cohesive that they're cut with a knife. This consistency is created by particular strains of cream culture bacteria that produce long strands of starch-like carbohydrate. The stretchy carbohydrate absorbs water and sticks to casein particles, so manufacturers are using ropy strains of Streptococcus salivarius Streptococcus salivarius as natural stabilizers of yogurt and other cultured products. as natural stabilizers of yogurt and other cultured products.

Cooking with Fermented Milks Most cultured milk products are especially susceptible to curdling when made into sauces or added to other hot foods. Fresh milk and cream are relatively stable, but the extended heat treatment and high acidity characteristic of cultured products have already caused some protein coagulation. Anything the cook does to push this coagulation further will cause the protein network to shrink and squeeze out some of the whey and produce distinct white particles - protein curds - floating in the thinned liquid. Heat, salt, additional acid, and vigorous stirring can all cause curdling. The key to maintaining a smooth texture is gentleness. Heat gradually and moderately, and stir slowly.

There is a common misconception that creme fraiche is uniquely immune to curdling. It's true that while yogurt, sour cream, and b.u.t.termilk all will curdle if they get anywhere near the boil, creme fraiche can be boiled with impunity. But this versatility has nothing to do with fermentation: it's a simple matter of fat content. Heavy cream, at 38 to 40% fat, has so little protein that it doesn't form noticeable curds (p. 29).

Cheese Cheese is one of the great achievements of humankind. Not any cheese in particular, but cheese in its astonishing multiplicity, created anew every day in the dairies of the world. Cheese began as a simple way of concentrating and preserving the bounty of the milking season. Then the attentiveness and ingenuity of its makers slowly transformed it into something more than mere physical nourishment: into an intense, concentrated expression of pastures and animals, of microbes and time.

The Evolution of Cheese Cheese is a modified form of milk that is more concentrated, more durable, and more flavorful food than milk is. It's made more concentrated by curdling milk and removing much of its water. The nutritious curds of protein and fat are made more durable by the addition of acid and salt, which discourage the growth of spoilage microbes. And they're made more flavorful by the controlled activity of milk and microbe enzymes, which break the protein and fat molecules apart into small flavorful fragments.

Unusual Fermented Milks: Koumiss and KefirBecause milk contains an appreciable amount of the sugar lactose, it can be fermented like grape juice and other sugary fluids into an alcoholic liquid. This fermentation requires unusual lactose-fermenting yeasts (species of Saccharomyces, Torula, Candida, Saccharomyces, Torula, Candida, and and Kluyveromyces Kluyveromyces). For thousands of years, the nomads of central Asia have made koumiss koumiss from mare's milk, which is especially rich in lactose, and this tart, effervescent drink, with 12% alcohol and 0.51% acid, remains very popular there and in Russia. Other European and Scandinavian peoples have made alcoholic products from other milks, as well as sparkling "wine" from whey. from mare's milk, which is especially rich in lactose, and this tart, effervescent drink, with 12% alcohol and 0.51% acid, remains very popular there and in Russia. Other European and Scandinavian peoples have made alcoholic products from other milks, as well as sparkling "wine" from whey.Another remarkable fermented milk little known in the West is kefir, kefir, which is most popular in the Caucasus and may well have originated there. Unlike other fermented milks, in which the fermenting microbes are evenly dispersed, kefir is made by large, complex particles known as kefir grains, which house a dozen or more kinds of microbes, including lactobacilli, lactococci, yeasts, and vinegar bacteria. This symbiotic a.s.sociation grows at cool room temperatures to produce a tart, slightly alcoholic, effervescent, creamy product. which is most popular in the Caucasus and may well have originated there. Unlike other fermented milks, in which the fermenting microbes are evenly dispersed, kefir is made by large, complex particles known as kefir grains, which house a dozen or more kinds of microbes, including lactobacilli, lactococci, yeasts, and vinegar bacteria. This symbiotic a.s.sociation grows at cool room temperatures to produce a tart, slightly alcoholic, effervescent, creamy product.

The long evolution of cheese probably began around 5,000 years ago, when people in warm central Asia and the Middle East learned that they could preserve naturally soured, curdled milk by draining off the watery whey and salting the concentrated curds. At some point they also discovered that the texture of the curd became more pliable and more cohesive if the curdling took place in an animal stomach or with pieces of stomach in the same container. These first cheeses may have resembled modern brine-cured feta, which is still an important cheese type in the eastern Mediterranean and the Balkans. The earliest good evidence of cheesemaking known to date, a residue found in an Egyptian pot, dates from around 2300 BCE BCE.

The Ingredient Essential to Diverse Cheeses: Time This basic technique of curdling milk with the help of the stomach extract now called rennet, then draining and brining the curds, was eventually carried west and north into Europe. Here people gradually discovered that curds would keep well enough in these cooler regions with much milder treatments: a less puckery souring and only a modest brining or salting. This was the discovery that opened the door to the great diversification of cheeses, because it introduced a fifth ingredient after milk, milk bacteria, rennet, and salt: time. In the presence of moderate acidity and salt, cheese became a hospitable medium for the continuing growth and activity of a variety of microbes and their enzymes. In a sense, cheese came to life. It became capable of p.r.o.nounced development and change; it entered the cyclical world of birth, maturation, and decline. This basic technique of curdling milk with the help of the stomach extract now called rennet, then draining and brining the curds, was eventually carried west and north into Europe. Here people gradually discovered that curds would keep well enough in these cooler regions with much milder treatments: a less puckery souring and only a modest brining or salting. This was the discovery that opened the door to the great diversification of cheeses, because it introduced a fifth ingredient after milk, milk bacteria, rennet, and salt: time. In the presence of moderate acidity and salt, cheese became a hospitable medium for the continuing growth and activity of a variety of microbes and their enzymes. In a sense, cheese came to life. It became capable of p.r.o.nounced development and change; it entered the cyclical world of birth, maturation, and decline.

When were modern cheeses born? We don't really know, but it was well before Roman times. In his Rei rusticae Rei rusticae ("On Rustic Matters," about 65 ("On Rustic Matters," about 65 CE CE), Columella describes at length what amounts to standard cheesemaking practice. The curdling was done with rennet or various plant fluids. The whey was pressed out, the curds sprinkled with salt, and the fresh cheese put in a shady place to harden. Salting and hardening were repeated, and the ripe cheese was then washed, dried, and packed for storage and shipping. Pliny, who also wrote in the first century, said that Rome most esteemed cheeses from its provincial outposts, especially Nimes in southern France, and the French and Dalmatian Alps.

The Growth of Diversity During the 10 or 12 centuries after Rome's strong rule, the art of cheesemaking progressed in the feudal estates and monasteries, which worked steadily at settling in forested areas or mountain meadows and clearing the land for grazing. These widely dispersed communities developed their cheesemaking techniques independently to suit their local landscape, climate, materials, and markets. Small, perishable soft cheeses, often made from the milk of a few household animals, were consumed locally and quickly and could only be sent to nearby towns. Large hard cheeses required the milk of many animals and were often made by cooperatives (the Gruyere During the 10 or 12 centuries after Rome's strong rule, the art of cheesemaking progressed in the feudal estates and monasteries, which worked steadily at settling in forested areas or mountain meadows and clearing the land for grazing. These widely dispersed communities developed their cheesemaking techniques independently to suit their local landscape, climate, materials, and markets. Small, perishable soft cheeses, often made from the milk of a few household animals, were consumed locally and quickly and could only be sent to nearby towns. Large hard cheeses required the milk of many animals and were often made by cooperatives (the Gruyere fruiteries fruiteries began around 1200); they kept indefinitely and could be transported to market from distant regions. The result was a remarkable diversity of traditional cheeses, which number from 20 to 50 in most countries and several hundred in France alone, thanks to its size and range of climates. began around 1200); they kept indefinitely and could be transported to market from distant regions. The result was a remarkable diversity of traditional cheeses, which number from 20 to 50 in most countries and several hundred in France alone, thanks to its size and range of climates.

Cheeses as ArtifactsBehind every cheese there is a pasture of a different green under a different sky: meadows encrusted with salt that the tides of Normandy deposit every evening; meadows perfumed with aromas in the windy sunlight of Provence; there are different herds, with their shelters and their movements across the countryside; there are secret methods handed down over the centuries. This shop is a museum: Mr. Palomar, visiting it, feels as he does in the Louvre, behind every displayed object the presence of the civilization that gave it form and takes form from it.- Italo Calvino, Palomar, Palomar, 1983 1983Charlemagne Learns to Eat Moldy CheeseDuring the Middle Ages, when cheese was evolving into a finely crafted food, even an emperor of France had to learn a thing or two about how to appreciate it. About 50 years after Charlemagne's death in 814, an anonymous monk at the monastery of Saint Gall wrote a biography of him that includes this fascinating anecdote (slightly modified from Early Lives of Charlemagne Early Lives of Charlemagne, transl. A. J. Grant, 1922). Charlemagne was traveling, and found himself at a bishop's residence at dinnertime.Now on that day, being the sixth day of the week, he was not willing to eat the flesh of beast or bird. The bishop, being by reason of the nature of the place unable to procure fish immediately, ordered some excellent cheese, white with fat, to be placed before him. Charles...required nothing else, but taking up his knife and throwing away the mold, which seemed to him abominable, he ate the white of the cheese. Then the bishop, who was standing nearby like a servant, drew close and said "Why do you do that, lord Emperor? You are throwing away the best part." On the persuasion of the bishop, Charles...put a piece of the mold in his mouth, and slowly ate it and swallowed it like b.u.t.ter. Then, approving the bishop's advice, he said "Very true, my good host," and he added, "Be sure to send me every year to Aix two cartloads of such cheeses."The word I've translated as "mold" is aerugo aerugo in the Latin: literally, "the rust of copper." The cheese isn't named, and some writers have deduced that it was a Brie, which then had an external coat of gray-green mold, much the same color as weathered copper. But I think it was probably more like Roquefort, a sheep's-milk cheese veined internally with blue-green mold. The rest of the anecdote fits a large, firm, internally ripened cheese better than a thin, soft Brie. It also marks what may have been the first appointment of an official cheese affineur! in the Latin: literally, "the rust of copper." The cheese isn't named, and some writers have deduced that it was a Brie, which then had an external coat of gray-green mold, much the same color as weathered copper. But I think it was probably more like Roquefort, a sheep's-milk cheese veined internally with blue-green mold. The rest of the anecdote fits a large, firm, internally ripened cheese better than a thin, soft Brie. It also marks what may have been the first appointment of an official cheese affineur!The bishop was alarmed at the impossibility of the task and...rejoined: "My lord, I can procure the cheeses, but I cannot tell which are of this quality and which of another...." Then Charles...spoke thus to the bishop, who from childhood had known such cheeses and yet could not test them. "Cut them in two," he said, "then fasten together with a skewer those that you find to be of the right quality and keep them in your cellar for a time and then send them to me. The rest you may keep for yourself and your clergy and family."

Cheeses of Reputation The art of cheesemaking had progressed enough by late medieval times to inspire connoisseurship. The French court received shipments from Brie, Roquefort, Comte, Maroilles, and Gerome (Munster). Cheeses made near Parma in Italy and near Appenzell in Switzerland were renowned throughout Europe. In Britain, Cheshire cheese was famous by Elizabethan times, and Cheddar and Stilton by the 18th century. Cheese played two roles: for the poor, fresh or briefly ripened types were staple food, sometimes called "white meat," while the rich enjoyed a variety of aged cheeses as one course of their multicourse feasts. By the early 19th century, the French gastronome Brillat-Savarin found cheese to be an aesthetic necessity: he wrote that "a dessert without cheese is like a beautiful woman who is missing an eye." The golden age of cheese was probably the late 19th and early 20th centuries, when the art was fully developed, local styles had developed and matured, and the railroads brought country products to the city while they were still at their best. The art of cheesemaking had progressed enough by late medieval times to inspire connoisseurship. The French court received shipments from Brie, Roquefort, Comte, Maroilles, and Gerome (Munster). Cheeses made near Parma in Italy and near Appenzell in Switzerland were renowned throughout Europe. In Britain, Cheshire cheese was famous by Elizabethan times, and Cheddar and Stilton by the 18th century. Cheese played two roles: for the poor, fresh or briefly ripened types were staple food, sometimes called "white meat," while the rich enjoyed a variety of aged cheeses as one course of their multicourse feasts. By the early 19th century, the French gastronome Brillat-Savarin found cheese to be an aesthetic necessity: he wrote that "a dessert without cheese is like a beautiful woman who is missing an eye." The golden age of cheese was probably the late 19th and early 20th centuries, when the art was fully developed, local styles had developed and matured, and the railroads brought country products to the city while they were still at their best.

Modern Decline The modern decline of cheesemaking has its roots in that same golden age. Cheese and b.u.t.ter factories were born in the United States, a country with no cheesemaking tradition, just 70 years after the Revolution. In 1851, an upstate New York dairy farmer named Jesse Williams agreed to make cheese for neighboring farms, and by the end of the Civil War there were hundreds of such "a.s.sociated" dairies, whose economic advantages brought them success throughout the industrialized world. In the 1860s and '70s, pharmacies and then pharmaceutical companies began ma.s.s-producing rennet. At the turn of the century scientists in Denmark, the United States, and France brought more standardization in the form of pure microbial cultures for curdling and ripening cheese, which had once been accomplished by the local, complex flora of each cheesemaker's dairy. The modern decline of cheesemaking has its roots in that same golden age. Cheese and b.u.t.ter factories were born in the United States, a country with no cheesemaking tradition, just 70 years after the Revolution. In 1851, an upstate New York dairy farmer named Jesse Williams agreed to make cheese for neighboring farms, and by the end of the Civil War there were hundreds of such "a.s.sociated" dairies, whose economic advantages brought them success throughout the industrialized world. In the 1860s and '70s, pharmacies and then pharmaceutical companies began ma.s.s-producing rennet. At the turn of the century scientists in Denmark, the United States, and France brought more standardization in the form of pure microbial cultures for curdling and ripening cheese, which had once been accomplished by the local, complex flora of each cheesemaker's dairy.

The crowning blow to cheese diversity and quality was World War II. In continental Europe, agricultural lands became battlefields, and dairying was devastated. During the prolonged recovery, quality standards were suspended, factory production was favored for its economies of scale and ease of regulation, and consumers were grateful for any approximation of the prewar good life. Inexpensive standardized cheese rose to dominance. Ever since, most cheese in Europe and the United States has been made in factories. Even in France, which in 1973 established a certification program ("Fromage appellation d'origine controlee") to indicate that a cheese has been made by traditional methods and in the traditional area of production, less than 20% of the total national production qualifies. In the United States, the market for process cheese, process cheese, a mixture of aged and fresh cheeses blended with emulsifiers and repasteurized, is now larger than the market for "natural" cheese, which itself is almost exclusively factory-made. a mixture of aged and fresh cheeses blended with emulsifiers and repasteurized, is now larger than the market for "natural" cheese, which itself is almost exclusively factory-made.

At the beginning of the 21st century, most cheese is an industrial product, an expression not of diverse natural and human particulars, but of the monolithic imperatives of standardization and efficient ma.s.s production. Industrial cheese also requires great ingenuity, has its economic merits, and suits its primary role as an ingredient in fast-food sandwiches, snacks, and prepared foods (a role that doubled U.S. per capita cheese consumption between 1975 and 2001). But in its own way, industrial cheese is a throwback to primitive cheese, a simplified food that could be and is made anywhere, and that tastes of nowhere in particular.

The Revival of Tradition and Quality Though finely crafted cheeses will always be a minor part of modern dairy production, recent years have brought modest signs of hope. The postwar era and its economic limitations have faded. Some European countries have seen a revival of appreciation for traditional cheeses, and air travel has brought them to the attention of an ever-growing number of food lovers. Once "white meat" for the rural poor, they are now pricey treats for the urban middle cla.s.s. In the United States, a few small producers blend respect for tradition with 21st century understanding, and make superb cheeses of their own. For enthusiasts willing to seek them out, the world still offers delightful expressions of this ancient craft. Though finely crafted cheeses will always be a minor part of modern dairy production, recent years have brought modest signs of hope. The postwar era and its economic limitations have faded. Some European countries have seen a revival of appreciation for traditional cheeses, and air travel has brought them to the attention of an ever-growing number of food lovers. Once "white meat" for the rural poor, they are now pricey treats for the urban middle cla.s.s. In the United States, a few small producers blend respect for tradition with 21st century understanding, and make superb cheeses of their own. For enthusiasts willing to seek them out, the world still offers delightful expressions of this ancient craft.

The Ingredients of Cheese The three princ.i.p.al ingredients of cheese are milk, rennet enzymes that curdle the milk, and microbes that acidify and flavor the milk. Each strongly influences the character and quality of the final cheese.

Milks Cheese is milk concentrated five- to tenfold by the removal of water; so the basic character of the milk defines the basic character of the cheese. Milk character is in turn determined by the kind of animal that produces it, what the animal eats, the microbes that inhabit the milk, and whether it is raw or pasteurized. Cheese is milk concentrated five- to tenfold by the removal of water; so the basic character of the milk defines the basic character of the cheese. Milk character is in turn determined by the kind of animal that produces it, what the animal eats, the microbes that inhabit the milk, and whether it is raw or pasteurized.

Species The milks of cows, sheep, and goats taste different from each other (p. 21), and their cheeses do too. Cow's milk is more neutral than other milks. Sheep and buffalo milk have relatively high fat and protein contents and therefore make richer cheeses. Goat's milk has a relatively low proportion of curdle-able casein and usually produces a crumbly, less cohesive curd compared to other milks. The milks of cows, sheep, and goats taste different from each other (p. 21), and their cheeses do too. Cow's milk is more neutral than other milks. Sheep and buffalo milk have relatively high fat and protein contents and therefore make richer cheeses. Goat's milk has a relatively low proportion of curdle-able casein and usually produces a crumbly, less cohesive curd compared to other milks.

Breed During the spread of cheesemaking in the Middle Ages, hundreds of different dairy animal varieties were bred to make the best use of local pasturage. The Brown Swiss is thought to go back several thousand years. Today, most of these locally adapted breeds have been replaced by the omnipresent black-and-white Holstein or Friesian, bred to maximize the milk it yields on standardized feed. Traditional breeds produce a lower volume of milk, but a milk richer in protein, fat, and other desirable cheese const.i.tuents. During the spread of cheesemaking in the Middle Ages, hundreds of different dairy animal varieties were bred to make the best use of local pasturage. The Brown Swiss is thought to go back several thousand years. Today, most of these locally adapted breeds have been replaced by the omnipresent black-and-white Holstein or Friesian, bred to maximize the milk it yields on standardized feed. Traditional breeds produce a lower volume of milk, but a milk richer in protein, fat, and other desirable cheese const.i.tuents.

Feed: The Influence of the Seasons Today most dairy animals are fed year-round on silage and hay made from just a few fodder crops (alfalfa, maize). This standard regimen produces a standard, neutral milk that can be made into very good cheese. However, herds let out to pasture to eat fresh greenery and flowers give milk of greater aromatic complexity that can make extraordinary cheese. Thanks to newly sensitive a.n.a.lytical instruments, dairy chemists have recently verified what connoisseurs have known for centuries: an animal's diet influences its milk and the cheese made from it. French studies of alpine Gruyere found a larger number of flavor compounds in cheeses made during summer pasturage compared to winter stable feeding, and more herbaceous and floral terpenes and other aromatics (p. 273) in mountain cheeses than cheeses from the high plateaus, which in turn have more than cheeses from the plains (alpine meadows have more diverse vegetation than the gra.s.sy lowlands). Today most dairy animals are fed year-round on silage and hay made from just a few fodder crops (alfalfa, maize). This standard regimen produces a standard, neutral milk that can be made into very good cheese. However, herds let out to pasture to eat fresh greenery and flowers give milk of greater aromatic complexity that can make extraordinary cheese. Thanks to newly sensitive a.n.a.lytical instruments, dairy chemists have recently verified what connoisseurs have known for centuries: an animal's diet influences its milk and the cheese made from it. French studies of alpine Gruyere found a larger number of flavor compounds in cheeses made during summer pasturage compared to winter stable feeding, and more herbaceous and floral terpenes and other aromatics (p. 273) in mountain cheeses than cheeses from the high plateaus, which in turn have more than cheeses from the plains (alpine meadows have more diverse vegetation than the gra.s.sy lowlands).

Like fruits, cheeses made from pasturefed animals are seasonal. The season depends on the local climate - the summer is green in the Alps, the winter in California - and how long it takes a particular cheese to mature. Cheeses made from pasturage are generally recognizable by their deeper yellow color, due to the greater content of carotenoid pigments in fresh vegetation (p. 267). (Bright orange cheeses have been dyed.) Pasteurized and Raw Milks In modern cheese production, the milk is almost always pasteurized to eliminate disease and spoilage bacteria. This is really a practical necessity in industrial cheesemaking, which requires that milk be pooled and stored from many farms and thousands of animals. The risk of contamination - which only takes one diseased cow or dirty udder - is too great. Since the late 1940s, the U.S. Food and Drug Administration has required that any cheese made from unpasteurized, "raw" milk must be aged a minimum of 60 days at a temperature above 35F/2C, conditions that are thought to eliminate whatever pathogens might have been in the milk; and since the early 1950s it has also banned the import of raw-milk cheeses aged less than 60 days. This means that soft cheeses made with raw milk are essentially contraband in the United States. The World Health Organization has considered recommending a complete ban on the production of raw-milk cheeses. In modern cheese production, the milk is almost always pasteurized to eliminate disease and spoilage bacteria. This is really a practical necessity in industrial cheesemaking, which requires that milk be pooled and stored from many farms and thousands of animals. The risk of contamination - which only takes one diseased cow or dirty udder - is too great. Since the late 1940s, the U.S. Food and Drug Administration has required that any cheese made from unpasteurized, "raw" milk must be aged a minimum of 60 days at a temperature above 35F/2C, conditions that are thought to eliminate whatever pathogens might have been in the milk; and since the early 1950s it has also banned the import of raw-milk cheeses aged less than 60 days. This means that soft cheeses made with raw milk are essentially contraband in the United States. The World Health Organization has considered recommending a complete ban on the production of raw-milk cheeses.

Of course until barely a century ago, nearly all cheeses were made in small batches with raw milk, fresh from the udders of small herds whose health was more easily monitored. And French, Swiss, and Italian regulations actually forbid forbid the use of pasteurized milk for the traditional production of a number of the world's greatest cheeses, including Brie, Camembert, Comte, Emmental, Gruyere, and Parmesan. The reason is that pasteurization kills useful milk bacteria, and inactivates many of the milk's own enzymes. It thus eliminates two of the four or five sources of flavor development during ripening, and prevents traditional cheeses from living up to their own standards of excellence. the use of pasteurized milk for the traditional production of a number of the world's greatest cheeses, including Brie, Camembert, Comte, Emmental, Gruyere, and Parmesan. The reason is that pasteurization kills useful milk bacteria, and inactivates many of the milk's own enzymes. It thus eliminates two of the four or five sources of flavor development during ripening, and prevents traditional cheeses from living up to their own standards of excellence.

Pasteurization is no guarantee of safety, because the milk or cheese can be contaminated during later processing. Nearly all outbreaks of food poisoning from milk or cheese in recent decades have involved pasteurized products. It will be genuine progress when public health officials help ambitious cheesemakers to ensure the safety of raw-milk cheeses, rather than making rules that restrict consumer choice without significantly reducing risk.

The Key Catalyst: Rennet The making and use of rennet was humankind's first venture in biotechnology. At least 2,500 years ago, shepherds began to use pieces of the first stomach of a young calf, lamb, or goat to curdle milk for cheese; and sometime later they began to make a brine extract from the stomach. That extract was the world's first semipurified enzyme. Now, by means of genetic engineering, modern biotechnology produces a pure version of the same calf enzyme, called The making and use of rennet was humankind's first venture in biotechnology. At least 2,500 years ago, shepherds began to use pieces of the first stomach of a young calf, lamb, or goat to curdle milk for cheese; and sometime later they began to make a brine extract from the stomach. That extract was the world's first semipurified enzyme. Now, by means of genetic engineering, modern biotechnology produces a pure version of the same calf enzyme, called chymosin, chymosin, in a bacterium, a mold, and a yeast. Today, most cheese in the United States is made with these engineered "vegetable rennets," and less than a quarter with traditional rennet from calf stomach (which is often required for traditional European cheeses). in a bacterium, a mold, and a yeast. Today, most cheese in the United States is made with these engineered "vegetable rennets," and less than a quarter with traditional rennet from calf stomach (which is often required for traditional European cheeses).

The curdling of milk by the rennet enzyme chymosin. The bundled micelles of casein in milk are kept separate from each other by electrically charged micelle components that repel each other (left). (left). Chymosin selectively trims away these charged kappa-caseins, and the now uncharged micelles bond to each other to form a continuous meshwork Chymosin selectively trims away these charged kappa-caseins, and the now uncharged micelles bond to each other to form a continuous meshwork (right). (right). The liquid milk coagulates into a moist solid. The liquid milk coagulates into a moist solid.

The Curdling Specialist Traditional rennet is made from the fourth stomach or abomasum of a milk-fed calf less than 30 days old, before chymosin is replaced by other protein-digesting enzymes. The key to rennet's importance in cheesemaking is chymosin's specific activity. Where other enzymes attack most proteins at many points and break them into many pieces, chymosin effectively attacks only one milk protein, and at just one point. Its target is the negatively charged kappa-casein (p. 19) that repels individual casein particles from each other. By clipping these pieces off, chymosin allows the casein particles to bond to each other and form a continuous solid gel, the curd. Traditional rennet is made from the fourth stomach or abomasum of a milk-fed calf less than 30 days old, before chymosin is replaced by other protein-digesting enzymes. The key to rennet's importance in cheesemaking is chymosin's specific activity. Where other enzymes attack most proteins at many points and break them into many pieces, chymosin effectively attacks only one milk protein, and at just one point. Its target is the negatively charged kappa-casein (p. 19) that repels individual casein particles from each other. By clipping these pieces off, chymosin allows the casein particles to bond to each other and form a continuous solid gel, the curd.

Since plain acidity alone causes milk to curdle, why do cheesemakers need rennet at all? There are two reasons. First, acid disperses the casein micelle proteins and their calcium glue before it allows the proteins to come together, so some casein and most of the calcium are lost in the whey, and the remainder forms a weak, brittle curd. By contrast, rennet leaves the micelles mostly intact and causes each to bond to several others into a firm, elastic curd. Second, the acidity required to curdle casein is so high that flavor-producing enzymes in the cheese work very slowly or not at all.

Cheese Microbes Cheeses are decomposed and recomposed by a colorful cast of microbes, perhaps a handful in most modern cheeses made with purified cultures, but dozens in some traditional cheeses made with a portion of the previous batch's starter. Cheeses are decomposed and recomposed by a colorful cast of microbes, perhaps a handful in most modern cheeses made with purified cultures, but dozens in some traditional cheeses made with a portion of the previous batch's starter.

Starter Bacteria First there are the lactic acid bacteria that initially acidify the milk, persist in the drained curd, and generate much of the flavor during the ripening of many semihard and hard cheeses, including Cheddar, Gouda, and Parmesan. The numbers of live First there are the lactic acid bacteria that initially acidify the milk, persist in the drained curd, and generate much of the flavor during the ripening of many semihard and hard cheeses, including Cheddar, Gouda, and Parmesan. The numbers of live starter starter bacteria in the curd often drop drastically during cheesemaking, but their enzymes survive and continue to work for months, breaking down proteins into savory amino acids and aromatic by-products (see box, p. 62). There are two broad groups of starters: the moderate-temperature lactococci that are also used to make cultured creams, and the heat-loving lactobacilli and streptococci that are also used to make yogurt (p. 48). Most cheeses are acidified by the mesophilic group, while the few that undergo a cooking step - mozzarella, the alpine and Italian hard cheeses - are acidified by thermophiles that can survive and continue to contribute flavor. Many Swiss and Italian starters are still only semidefined mixtures of heat-loving milk bacteria, and are made the old-fashioned way, from the whey of the previous batch. bacteria in the curd often drop drastically during cheesemaking, but their enzymes survive and continue to work for months, breaking down proteins into savory amino acids and aromatic by-products (see box, p. 62). There are two broad groups of starters: the moderate-temperature lactococci that are also used to make cultured creams, and the heat-loving lactobacilli and streptococci that are also used to make yogurt (p. 48). Most cheeses are acidified by the mesophilic group, while the few that undergo a cooking step - mozzarella, the alpine and Italian hard cheeses - are acidified by thermophiles that can survive and continue to contribute flavor. Many Swiss and Italian starters are still only semidefined mixtures of heat-loving milk bacteria, and are made the old-fashioned way, from the whey of the previous batch.

True "Vegetable Rennets" from Thistle FlowersIt has been known at least since Roman times that some plant materials can curdle milk. Two have been used for centuries to make a distinctive group of cheeses. In Portugal and Spain, flowers of the wild cardoon thistles (Cynara cardunculus and and C. humilis C. humilis) have long been collected and dried in the summer, and then soaked in warm water in the winter to make sheep and goat cheeses (Portuguese Serra, Serpa, Azeito; Spanish Serena, Torta del Casar, Pedroches). The cardoon rennets are unsuited to cow's milk, which they curdle but also turn bitter. Recent research has revealed that Iberian shepherds had indeed found a close biochemical relative of calf chymosin, which the thistle flower happens to concentrate in its stigmas.

The Propionibacteria An important bacterium in Swiss starter cultures is An important bacterium in Swiss starter cultures is Propionibacter shermanii, Propionibacter shermanii, the hole-maker. The propionibacteria consume the cheese's lactic acid during ripening, and convert it to a combination of propionic and acetic acids and carbon dioxide gas. The acids' aromatic sharpness, together with b.u.t.tery diacetyl, contributes to the distinctive flavor of Emmental, and the carbon dioxide forms bubbles, or the characteristic "holes." The propionibacteria grow slowly, and the cheesemaker must coddle them along by ripening the cheese at an unusually high temperature - around 75F/24C - for several weeks. This need for warmth may reflect the cheese propionibacteria's original home, which was probably animal skin. (At least three other species of propionibacteria inhabit moist or oily areas of human skin, and the hole-maker. The propionibacteria consume the cheese's lactic acid during ripening, and convert it to a combination of propionic and acetic acids and carbon dioxide gas. The acids' aromatic sharpness, together with b.u.t.tery diacetyl, contributes to the distinctive flavor of Emmental, and the carbon dioxide forms bubbles, or the characteristic "holes." The propionibacteria grow slowly, and the cheesemaker must coddle them along by ripening the cheese at an unusually high temperature - around 75F/24C - for several weeks. This need for warmth may reflect the cheese propionibacteria's original home, which was probably animal skin. (At least three other species of propionibacteria inhabit moist or oily areas of human skin, and P. acnes P. acnes takes advantage of plugged oil glands.) takes advantage of plugged oil glands.) The Smear Bacteria The bacterium that gives Munster, Epoisses, Limburger, and other strong cheeses their p.r.o.nounced stink, and contributes more subtly to the flavor of many other cheeses, is The bacterium that gives Munster, Epoisses, Limburger, and other strong cheeses their p.r.o.nounced stink, and contributes more subtly to the flavor of many other cheeses, is Brevibacterium linens. Brevibacterium linens. As a group, the brevibacteria appear to be natives of two salty environments: the seash.o.r.e and human skin. Brevibacteria grow at salt concentrations that inhibit most other microbes, up to 15% (seawater is just 3%). Unlike the starter species, the brevibacteria don't tolerate acid and need oxygen, and grow only on the cheese surface, not inside. The cheesemaker encourages them by wiping the cheese periodically with brine, which causes a characteristic sticky, orange-red "smear" of brevibacteria to develop. (The color comes from a carotene-related pigment; exposure to light usually intensifies the color.) They contribute a more subtle complexity to cheeses that are wiped for only part of the ripening (Gruyere) or are ripened in humid conditions (Camembert). Smear cheeses are so reminiscent of cloistered human skin because both As a group, the brevibacteria appear to be natives of two salty environments: the seash.o.r.e and human skin. Brevibacteria grow at salt concentrations that inhibit most other microbes, up to 15% (seawater is just 3%). Unlike the starter species, the brevibacteria don't tolerate acid and need oxygen, and grow only on the cheese surface, not inside. The cheesemaker encourages them by wiping the cheese periodically with brine, which causes a characteristic sticky, orange-red "smear" of brevibacteria to develop. (The color comes from a carotene-related pigment; exposure to light usually intensifies the color.) They contribute a more subtle complexity to cheeses that are wiped for only part of the ripening (Gruyere) or are ripened in humid conditions (Camembert). Smear cheeses are so reminiscent of cloistered human skin because both B. linens B. linens and its human cousin, and its human cousin, B. epidermidis, B. epidermidis, are very active at breaking down protein into molecules with fishy, sweaty, and garlicky aromas (amines, isovaleric acid, sulfur compounds). These small molecules can diffuse into the cheese and affect both flavor and texture deep inside. are very active at breaking down protein into molecules with fishy, sweaty, and garlicky aromas (amines, isovaleric acid, sulfur compounds). These small molecules can diffuse into the cheese and affect both flavor and texture deep inside.

Why Some People Can't Stand CheeseThe flavor of cheese can provoke ecstasy in some people and disgust in others. The 17th century saw the publication of at least two learned European treatises "de aversatione casei," or "on the aversion to cheese." And the author of "Fromage" in the 18th century Encyclopedie Encyclopedie noted that "cheese is one of those foods for which certain people have a natural repugnance, of which the cause is difficult to determine." Today the cause is clearer. The fermentation of milk, like that of grains or grapes, is essentially a process of limited, controlled spoilage. We allow certain microbes and their enzymes to decompose the original food, but not beyond the point of edibility. In cheese, animal fats and proteins are broken down into highly odorous molecules. Many of the same molecules are also produced during uncontrolled spoilage, as well as by mic