L'Etivaz and the Microbial Terroir of Cheese

Vicky Wasik

We're very excited to welcome Bronwen and Francis Percival back to the virtual pages of Serious Eats. We spoke with them about their love of cheese and their new book, Reinventing the Wheel: Milk, Microbes, and the Fight for Real Cheese, back in September, after which they wrote about Kirkham's Lancashire, one of their favorite examples of "real cheese." Here, they return to discuss another example: L'Etivaz.

The sun has just crested the alpine horizon as we reach the Chalet du Ruble, a remote wooden cabin at an elevation of nearly 2,000 meters in the Swiss canton of Vaud. It's July, and we're dripping with sweat as we struggle up the slope past placid Simmental cows, who seem much better adapted to the environment than their Anglo-Saxon visitors.

Erika Wisler welcomes us from the door of her small cheese room, its walls black from the smoke of the wood fire that burns beneath her 500-liter copper cauldron. We are just in time: The cauldron is full of milk, and she's about to start making L'Etivaz, the cheese that has made these mountains an object of turophile pilgrimage. It is a cheese that combines the sweetness of the alpine style with intense umami and a teasing edge of smoke from its close encounter with the wood fire. It is also a cheese that both challenges every facet of industrial modernity and offers us the chance to taste a farming system.

L'Etivaz is an alpage cheese, produced at altitude from the milk of cows grazing natural meadows. During the winter, these alpine meadows lie under deep snow, and the cattle reside on the valley floor, where they eat conserved forage and their milk is pooled and sent to the local dairy cooperative. There, the milk is used to produce generic soft cheeses intended for local consumption. This system of moving livestock between different environments with the season, known as transhumance, is used everywhere from the Alps to sheep farms and ranches in the western United States.

Alpage incarnations of cheeses like Beaufort and Gruyère exist, but are not the norm. In contrast, L'Etivaz is produced exclusively in the summer at altitude, during an official season that lasts from May 10 to October 10. The more remote chalets have even shorter seasons: The Wislers make cheese for just a few months each year, from the end of June to early September. The low yields of cows grazing in such a harsh environment, not to mention the inconvenience of decamping to the top of a mountain with one's entire family, make this a challenging proposition.

Milk and Modernity

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The pint of milk—fresh, sweet, and cold—is the essential dairy product. Or, at least, it is in the present-day Anglo-Saxon world. But everything about that milk is distinctively modern: its sweetness, its temperature, its liquidity. Those qualities require technologies like pasteurization, refrigeration, and efficient transport, all of which have contributed to the widespread availability of milk in its unfermented form.

Practices like refrigeration and mixing the milk from several herds have become second nature within the modern dairy industry. They allow for valuable economies of scale, and they can prolong milk's freshness (i.e., prevent it from naturally souring) for up to several days before further processing. This is not a consideration for large factories alone: Small-scale cheesemakers frequently make cheese only a few times a week, a practice that would have been impossible before the advent of refrigeration.

But, according to AOP mandates, the milk used for L'Etivaz must not travel more than a few yards from the moment the cows are milked to when it is made into cheese. The reason for this is that milk is surprisingly delicate, an emulsion of fat globules by diaphanous membranes. When warm, these globules are malleable and resilient, but when chilled, the fats inside them become rigid, like cold butter. Pumping and agitating cold milk—unavoidable when transport and refrigeration come into play—cause the globule membranes to shear, releasing the butterfat directly into the aqueous milk. This is the first step in churning butter, but for a cheesemaker interested in keeping that fat within the cheese, it's a disaster. When warmed back up for cheesemaking, the surface of milk that is old or over-pumped is laced with tiny butter-oil droplets, like a vinaigrette that's in the process of breaking. As the cheesemaking commences, these droplets or clumps of butterfat are carried off with the whey. (Folding the damaged fat back into the curd is even worse, leading to pockets of fat within the cheese.) By keeping cooling, pumping, and sloshing to an absolute minimum, processing the milk for L'Etivaz on-site prevents this damage in the first place.

Microbial Terroir

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Each farm is host to its own microbial ecosystems, with naturally occurring bacteria and fungi inhabiting every nook and cranny, including the soil in the pastures, the skin of the animals, and even the equipment used to make the cheese. The question is not just which microbes find their way into the milk, but which microbial strains evolve to suit each farm, as the subtly different conditions in different locations exert selective pressure on these organisms. Given our long generation times, vertebrate evolution takes many millennia; microbes, which can produce a new generation in as little as 20 minutes under the proper conditions, evolve at hyper-speed by comparison. (In a study of raw milk from farms in Normandy, microbiologists found wild-type strains of lactic acid bacteria, many of them unique to individual farms, that bore very little resemblance to the reference strains held at the government laboratory.)

Cheesemaking in an Etivaz chalet like the Wislers' is designed to exploit these native strains. Here, the evening milk is left in the dairy to cool gradually overnight. The temperature must never fall below 64°F (18°C), thus keeping the milk in the range where the lactic acid bacteria naturally present in the milk begin to multiply. These native lactic acid bacteria will play an important part in the fermentation of the milk during cheesemaking (see our previous piece on the mechanics of cheesemaking for more on this).

For this reason, the refrigeration of raw milk does not just damage the milk on a physical level; it is a decisive and negative intervention in the microbial balance. When milk is chilled, cold-loving bacteria have a selective advantage. These strains are never beneficial for flavor development, and their ranks include several spoilage bacteria and pathogens. This is the irony of refrigeration: While it delays spoilage in one sense, it also increases the potential for the dominance of bacteria that can ruin the cheese.

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The addition of soured whey from the previous day's make, incubated at a temperature selected to boost the number and vitality of the most useful strains, lends the native milk bacteria a helping hand. These bacteria multiply to high levels—up to a billion per gram—during the cheesemaking process. As the cheese matures, they gradually die off, releasing enzymes that go on to digest the milk fats and proteins, producing small aromatic and flavorful molecules. The AOP requirements of leaving the milk warm overnight and using whey starters full of native microbes mean we can taste the unique microbial community of each farm in the flavor of the finished cheese. Using these techniques, however, requires that the cheese be made every single day.

Both incubating the milk overnight and using whey starters can also be practiced on higher-yielding farms at low altitude, which have their own unique microbial populations. These techniques are thoroughly mainstream, required for cheeses as diverse as Parmigiano-Reggiano, Comté, and Beaufort. Nineteenth-century cheesemakers in England even flirted with employing whey starters for cheddar, ultimately discovering that the technique was not reliable in cheeses scalded to a lower temperature. The ubiquity of whey starters for these cooked-curd cheeses allows us to control for cheesemaking technique and taste the impact of site.

The Taste of Place

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When cows eat a high-energy diet rich in corn and concentrates—consisting of feeds that may contain soy, wheat, spent brewer's grains, palm oil derivatives, and sugar beet pulp, among other ingredients—their fats tell the tale. Beta-carotene, a fat-soluble vitamin with a golden color, is abundant in grass but almost absent in other feeds; it travels through the bloodstream and into the milk, where it gives grass-fed cream its golden color. Animals fed large amounts of energy-dense corn silage or concentrates do not receive the same amount of beta-carotene in their diet, and their cream is whiter as a result. (Species and breed also play a role, however: Breeds of cows such as Jerseys and Guernseys lack the ability to break down beta-carotene, so their fats are always yellower; meanwhile, goats and sheep metabolize it easily, making their milk and cheese bright white in color, regardless of their diet.)

A grass-rich diet also affects the type of fat in the milk. Just as with grass-fed beef, animals that eat grass produce milk fats that are less saturated than those of their corn-fed peers. Unsaturated fatty acids are softer; during summer, the butter from grazing herds becomes noticeably more spreadable, even when cold. When milk with more unsaturated fatty acids is made into cheese, the result is softer and more pliant. L'Etivaz, born of a diet rich in mountain grasses, is significantly yellower and softer than valley-floor cheese.

Moreover, all pastures are not created equal. The thin and poor soils high in the mountains promote a very different plant ecosystem from the grassland on the valley floor. Soil rich in organic matter supports the rapid growth of lush, leafy grasses, which quickly choke out more marginal members of the plant community—just the ticket if the purpose of the field is to provide high-energy food for grazing ruminants. By contrast, because of their low nutritive quality, poor soils don't support the same abundant foliage that grows on heavily fertilized fields, thus giving a competitive advantage to a wider variety of herbs and flowers. These include wild anemones, rock jasmine, and yellow gentians, as well as scrawnier grasses.

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Unlike lowland grasses, these plants produce a wide variety of aromatic compounds. We are most familiar with this family of molecules, known as terpenes, in their pure forms: strongly scented essential oils. Though studies have shown that, like beta-carotene, terpenes consumed by ruminants on wildflower-rich alpine pastures pass through into the milk, their low levels and evanescent nature make any effects on the flavor almost impossible to detect. This hasn't stopped some purveyors from exploiting the notion of these aromatic compounds to attract consumers—one maker of goat's cheese (who shall remain anonymous) invoked the thyme and lavender of the local brousse as the source of his cheese's herbal aroma, only to admit furtively afterward that nature might have had a little helping hand from a vial of essential oil. (In contrast, the heady sulfur compounds in wild garlic and onions come through loud and clear in the flavor of milk from animals that have grazed on them.)

Still, even though we cannot taste terpenes directly in cheeses, research led by Dr. Bruno Martin of the French National Institute for Agricultural Research (INRA) in central France has shown that this does not mean that terpenes make no difference in the flavor.

Martin and his team made hard, Cantal-style cheeses from the milk of otherwise-identical herds grazing on pasture with either low plant biodiversity or over 70 species per square meter. When the experimental cheeses were presented to a sensory panel at three months of age, the panel members could not find a significant difference between them, though they could immediately pick out a third cheese made from cows kept indoors on a high-concentrate diet—it was whiter, crumblier, and less aromatic. However, when the same set of cheeses was matured for six months, the tasters began to detect differences in the flavor intensity of the cheeses from different grazing systems. The tasters found that the cheeses made from high-diversity milk had a more intense aroma and pungent taste than their intensively grazed counterparts. Looking more closely at the results, Martin's team theorized that the differences were microbial, but that the terpenes were nonetheless playing a role. Essential oils, after all, are also known for their bioactive and antimicrobial properties. It appears that terpenes can impact the flavor of mature cheese not through their own aromatic properties, but by affecting which microbes can grow within the cheese, and the flavors that are produced in that way.

It is a tempting and poetic thought that cheese offers the potential to taste a place, and the work of researchers like Bruno Martin is starting to demonstrate the mechanisms through which this might be possible. What is becoming clear is that before we can taste the place, it must first be tasted by ruminants, then processed by the native microbial inhabitants of the farm and the milk. Cheese—particularly a cheese like L'Etivaz—is a field seen through the prism of its microbes.