Rennet, the catalyst of this alchemy, is stuff so strange as to be almost mythological. Ripped from the belly of a baby animal: And so it is, literally. Rennet comes from the lining of the first stomach of a calf, lamb, or baby goat. It contains an enzyme called chymosin, the function of which in a baby’s stomach is to curdle mother’s milk, thereby slowing its absorption and rearranging the milk proteins in such ways as to aid the baby’s digestion. Anyone who has ever burped a baby and been spit up on for his troubles, has observed the action of chymosin on milk.
Presumably some herder discovered the process several thousand years ago, when he or she slaughtered a young ruminant, opened up its stomach, and found some lumpy curds of milk. Or perhaps the ancient herder used the stomach of a young animal as a vessel in which to store or carry milk. Exposed to the rennet in the stomach lining, the milk would have turned to something much like cheese. Whatever its taste, the advantages of this “processed” milk over fresh would have been immediately apparent, particularly to a nomadic people in a time before refrigeration. Since curdling removes most of the water from the milk, it renders the food much more portable, and the curds, having been acidified in the animal’s stomach, would remain edible much longer than fresh milk.
What this suggests is that cheese was not so much an invention as a discovery. Like other fermentations, cheese making is a form of “biomimicry”—a technology modeled on a naturally occurring biological process. Certainly there was plenty of room for improving on stomach-curdled milk, including its taste and appearance and longevity. But, like other fermentations, cheese was from the beginning a boon to humankind: a perishable foodstuff that has been processed in such a way as to render it more digestible, more nutritious, more durable, and more flavorful than the original.
Rennet, which, remarkably, still often comes from the stomach linings of baby animals,* requires an acidic environment in order to best perform its magic of coagulation. In cheese making, the acid is supplied by bacterial fermentation rather than stomach acids. As in pickles and sauerkraut, the necessary bacteria are ubiquitous in the environment and on the “substrate”—in this case, the raw milk. But pasteurizing milk creates a biologically blank slate, into which cultures of lactobacilli must be reintroduced after pasteurization in order to acidify the milk and begin to build flavors. Starting with a clean slate has its advantages: The cheese maker can decide precisely which bacteria to introduce, and there will be few surprises—or “accidents de fromages,” as the French call their cheese-making disasters. That’s why such blank-slate ferments are now the rule, and not only in cheese-making. Most brewers and winemakers work the same way, killing off the native bacteria and yeasts and then reintroducing only the ones they want. Yet the gain in control of the process comes at the price of a loss in complexity that, according to proponents of raw-milk cheeses and other wild fermentations, you can taste.
One of the things you can taste in a raw-milk cheese is the taste of a particular place. For her dissertation research, Sister Noëlla drove around the French countryside, collecting samples of the microbes living on the rinds of various raw-milk cheeses. She focused her attention on Geotrichum candidum, a fungus I had never heard of but, it turns out, I have been eating large quantities of all my life: It is the mold that forms the downy white jacket on fungal-ripened cheeses like Camembert and Brie. (The French call it the jolie robe—“pretty dress.”) Using genetic-sequencing techniques to compare her samples, Sister Noëlla found “an enormous diversity” among strains of geotrichum. She also discovered that different strains of the same mold feasted on different nutrients in the milk, producing different chemical by-products that contribute different flavors to a cheese. She concluded that at least some part of the astounding diversity of French cheeses—“How can anyone be expected to govern a country with 246 cheeses?” Charles de Gaulle once famously asked—owes to the wide diversity of its microbes.
What this suggests is that terroir—the French term for the taste of place—is influenced not just by the local climate or soil but also by differences in the local bacteria and fungi. Sister Noëlla has come to think of this microbial biodiversity as part of a nation’s patrimony. “People understand the importance of preserving an endangered white rhino,” she told me. “But a strain of fungus no one has ever seen or even heard of is a tougher sell”—yet in her view no less important. As Italo Calvino wrote in Palomar:
Behind 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 [cheese] shop is a museum: … behind every displayed object the presence of the civilization that gave it form and takes form from it.
Later that afternoon, in her little laboratory on the abbey grounds, Sister Noëlla elaborated on the elusive concept of terroir. The particular taste of a place, as she conceives it, owes to a tight weave of natural and cultural threads that cannot readily be teased apart. Clearly the qualities of the milk (What breed were the cows? What plants grew in the pasture they grazed? What was the weather like?*) influence the flavor of a cheese, but so does even the tiniest detail in the technique of the cheese maker. And though we would tend to regard such details as artifacts of human culture rather than nature, their influence on the flavor of a cheese is mediated by microbes—that is, by nature. So, for example, the temperature in the vat; the time between steps; the tools used to cut the curd; the geometry of the molds into which they were pressed; how hard they are pressed; how much salt is introduced; the humidity in the cave; even the type of straw on which the cheeses rest as they age—all these details help to determine precisely which microbes will predominate, and these in turn help determine the sensory qualities of the finished cheese. (The rye straw? Sister Noëlla explained that rye grass favors the growth of Trichothecium roseum, “the flower of the molds”—lending a pinkish cast to the rind that is prized by the French.)
“A cheese is an ecological system,” Sister Noëlla explained, “and the cheese maker’s techniques operate like forces of natural selection to determine which species will succeed”—thereby creating the specific flavors and aromas and texture of a Saint-Nectaire rather than, say, a Mont d’Or or Reblochon. In this, a cheese is much like a sourdough bread culture, except that its microbial community is even more complex and long-lived. Indeed, it is still living when we eat it, whereas the culture in a bread dies in the oven.
When Lydie returned to the abbey two years after teaching Sister Noëlla to make cheese, she was astonished to find that the rind of a Connecticut Saint-Nectaire had developed the very same fungi as a Saint-Nectaire ripened in the Auvergne—up to and including the Trichothecium roseum. So was it possible Lydie had unwittingly carried those French microbes on her person during her first visit? Not likely, according to Sister Noëlla.
“Everything is everywhere,” she explains, referring to the numberless species of fungi and bacteria ubiquitous in the environment, “and then our technology selects” which among them will thrive. But wouldn’t this selection-by-culture argue against the idea of terroir? Only if your concept of terroir is limited to the local expression of nature. Yet a place is much more than a patch of earth; it is also the people who live in it and the traditions they follow, and so in turn the microbes they unconsciously favor—and which in turn have favored them, with desirable flavors and aromas. These highly particular qualities (which seem to be found in fermented foods especially*) owe at least partly to the reciprocal relationship of mic
robe and man—nature and culture together, as expressed through fermentation. So along with all the other elements contributing to the particular taste of a place—soil, climate, flora, tradition, technique, story—we need to add one more: the microbiology of human desire.
After Sister Noëlla had satisfied herself that the milk was sufficiently coagulated, she invited me to run my fingers through the pristine white Jell-O, gently breaking it up into tinier and tinier curds. I worked alongside the abbey’s newest postulant, Stephanie Cassidy. A willowy thirty-year-old with big brown eyes, Stephanie took care of the abbey’s cows and had recently begun helping out with the cheese making. Bending over the barrel from opposite sides, we ran our hands through the warm curd, carefully subdividing it into little white peas. The recipe specifies that the curd be kept at the same temperature as the cow’s body, so from time to time Sister Noëlla poured a little hot water along the inside edges of the barrel to keep it from cooling. When Stephanie judged the curds uniformly tiny enough, she took the wooden paddle from its nail and, running it slowly along the side of the barrel, began to herd the little curds together.
They seemed to like one another’s company. That’s because the chymosin in the rennet had snipped off a specific bit of one of the casein proteins that, in fresh milk, functions like a bumper to keep the particles bouncing off one another and so dispersed in solution. The milk coagulates when the now bumperless casein proteins bond to form a kind of mesh that traps fat and water. The goal in handling the curds is to gently expel the water from them while losing as little of the fat as possible.
The curds tasted sweet and clean but bland, more like fresh warm milk than cheese. But their blandness gave no hint of the frenzy of activity going on deep within them, as the curds formed and re-formed. Virtually all of the microbial DNA necessary to create a mature cheese was now present and accounted for and beginning to do its fermentative work. The lactobacilli were proliferating wildly in the warm milk, turning the lactose into lactic acid, contributing flavors, and lowering the pH, a souring process I could faintly smell. The acidification would continue in the cheese for several weeks before reversing course, as the fungi—also already present in the milk, as spores—took over, inaugurating a second fermentation in the rind. But I’m getting ahead of myself and the microbes. …
Once the wooden paddle had persuaded the curdlets to come together in a casual mass, Stephanie began removing the whey from the barrel with a flat-bottomed pan. Then, with the palms of her hands, she began pushing the mass of curd down toward the bottom of the barrel. I joined her, leaning over the barrel and pressing the curd down as slowly and gently as I possibly could, so as not to disturb the precious butterfat.
“Restez là,” Sister Noëlla implored us as we worked, explaining that that is what Lydie’s mother used to tell her whenever she had her hands on the curd. “Stay there”—move your hands as little and as gently as possible. Impatience would be ruinous; by forcing out the fat, it would make the paste—the interior of the cheese—rubbery. (Thus does the mood of the cheese maker find its way into a cheese.) The muscles in my wrists and lower back had begun to howl, but I kept at it, pressing down as slowly and deliberately as I could bear to. After decades of doing this kind of work several times a week, Sister Noëlla has had to have several surgeries to repair the carpal tunnel in her wrists.
At last Sister Noëlla pronounced herself satisfied with the curd. It now formed a three-inch-thick layer at the bottom of the barrel, snowy white beneath a few remaining inches of yellowish, sour whey. Standing up straight had never felt so wonderful. Alas, it was not to be for long. The time had come to cut the curd, and Stephanie handed me a long knife. She had me cut it in thirds, first top to bottom and then side to side. Then, with our hands, we scooped up the white bricks and piled them into the molds. Cylindrical containers the size of deep pie tins, the molds are made of wood or white plastic with a pattern of holes drilled into their bottoms. Now came more urgings to “restez là” as I slowly pressed the blocks of curd into the molds, turning them over from time to time. A thin trickle of whey wept from the holes. The curds were now tightly knit into something that looked and felt like a cheese, except that it was completely white and tasteless. We sprinkled some salt on the exposed side.
The term for these fresh discs is a “green cheese” and, incredibly, we had made only three of them from nearly fifty gallons of milk. Now, stacked one on top of another, the cheeses went into the press, an old wooden contraption with a big steel screw that could be manually tightened to gradually build pressure, squeezing still more water from the cheeses. We were done. The green cheeses would spend the night in the press, weeping their last few tears of whey, before being rinsed and moved into the “cave” the following morning. Here, they would spend the next two months, growing old.
Cheese is milk that has grown up. … It is preeminently the food of man—the older it grows the more manly it becomes, and in the last stages of senility it almost requires a room to itself. —Edward Bunyard (1878–1939), The Epicure’s Companion
Compared with other fermentations—of vegetables, grains, or grapes—the fermentation of fresh milk into a mature cheese depends on a remarkably complex dance of taxonomically far-flung species, including mammals, bacteria, and fungi. Or perhaps I should say fermentations, plural, because what takes place in the aging room is so different from what happens in the milk vat as to constitute a whole other order of transformation.
Most of the activity in the vat involves anaerobic bacteria turning lactose into lactic acids; that process continues in the paste—the airless interior of the cheese—with some elaborations, as enzymes produced by the bacteria break down fats, proteins, and sugars into simpler and generally more flavorful molecules. But as soon as the cheese maker forms the curds into, well, forms, she has created something new: an inside, the paste, and an outside, the incipient rind. Biologically, the rind comprises a new environment—airy and moist, but no longer wet—which selects for a new set of microbes: the aerobes. The spores of these aerobic microbes are already present (everything is everywhere) in the milk, in the air, clinging to the stone walls and earthen floor of the cave. And so, within hours, this new cast of microbial characters, beginning with a group of acid- and air-loving fungi, begins to colonize the wide-open frontier of the cheese rind.
Standing in the abbey’s “cave,” it is possible to observe this succession of species as if in time lapse. The cave is really just a ten-foot-square corner of a cellar, walled off and air-conditioned to maintain cavelike temperatures and levels of humidity all year long. Lining the walls are tall wooden cabinets faced with screen doors. Their shelves hold two months’ production of cheeses, arranged according to seniority. Written on the side of each cheese in blue ink is the date on which it was made and the initials of its maker. Starting with the fat white discs made yesterday, I could follow the cheeses’ progression from callow youth to venerable age, as the bloomy white rinds gradually take on some gray, then slowly mottle and shrink, until you arrive at the wrinkled and stinky gray-brown visage of a Saint-Nectaire that, after two months, is fully ripe and ready to eat.
What takes place in the rind over the course of these eight weeks is a more or less orderly form of rot. As successive rounds of decomposition unfold, one species dines on the waste products of another, in the process creating the conditions, and often the food, for the next. Most of these fungi you know well and have had reason to despise in the past: They are the same molds that turn white bread blue, that establish furry white beachheads on a ripe tomato or draw a dilating brown target on a pear. The cheese maker has learned, at least to an extent, how to manage or guide these familiar wild species, ge
tting them to behave in more or less predictable ways.
Sister Noëlla walked me through the stages of fungal life and death unfolding in her cave. By the second day, a fine lawn of yeasts—primarily Debaryomyces and Torulopsis—has spread across the fresh cheese, though it is only visible through a microscope. There are also invisible colonies of bacteria, such as Streptococcus cremoris, working to turn the lactose in the milk into lactic acid—food for future fungi. By the sixth day, the cheese has grown a fine white beard of hyphae from a fungus called Mucor. This particular fungus, which the French sometimes call the bête noire, is considered a catastrophe when it appears in a Brie or Camembert, but is warmly welcomed in a Saint-Nectaire or Tomme de Savoie. When on day nine the Mucur sporulates, a field of what (under the microscope) looks like black daisy seed heads colonizes the rind, transforming its pristine white to a grayish brown. By now the cheese looks as though it has lost its youthful innocence and acquired a few unsightly scars of experience. It has also visibly shrunk, as the water in it continues to evaporate.
In the shade of those blackish Mucor hyphae, strains of Geotrichum candidum, Sister Noëlla’s favorite fungus, are feasting on lactic acid and growing their own hyphae, though they are not yet visible to the naked eye. “Geo,” as some American cheese makers call it for short, is responsible for the downy white coat—the jolie robe—found on a Saint-Marcellin. The fungus introduces a set of powerful enzymes that break down various fats and proteins, in the process helping to develop the cheese’s flavor and releasing several strongly aromatic compounds, including the faint whiff of ammonia that filled the cave. Sister Noëlla has ultimate respect for Geotrichum, which was the subject of her dissertation. She mentioned that its enzymes have been known to bore holes through plastic. Some strains of Geo also seem to make it more difficult for Listeria to survive in a cheese.