How Does Milk Become Cheese?
Most of us know that milk is the primary ingredient in cheese. But, how does bland, fluid milk become dry, flavor-packed Parmigiano Reggiano? Or an oozy Brie with a velvety rind? Or a bold blue cheese like Roquefort?
In a word, magic.
In another word, fermentation.
While we think of cheese as an elegant snack, it's also just the controlled spoilage of milk. It's "milk's leap to immortality." It's dried-out milk solids. It's milk jerky. If you've ever left milk in your fridge for long enough to curdle, you've made a rudimentary (and not very tasty) form of cheese.
Cheese is the human-administered spoilage of milk, resulting in a less perishable, more delicious form of concentrated fat and protein. During this process, friendly bacteria are harnessed and harmful bacteria — called "pathogens" — are avoided. Cheese was invented as a practical way to store calories for longer than milk stayed fresh and now is simply a delicious, historic food that many of us choose to eat.
Cheesemaking: It Starts With Milk
Milk is 80 to 90 percent water — depending on the animal it comes from — plus fat, protein, sugar, and minerals. Some milk is heat-treated or "pasteurized" to kill any pathogens present before the milk is made into cheese. Critics claim that this process also kills potentially beneficial or flavor-driving bacteria and that carefully handled milk from healthy animals obviates the need for pasteurization.
Each country has different laws regarding pasteurization, but in the U.S., all cheeses that are aged less than 60 days must be pasteurized. As such, brie-style cheeses and fresh cheeses like mozzarella will be pasteurized in the U.S. 99.99 percent of the time.
If milk has not been pasteurized, it may be labeled as:
- Unpasteurized: which may have been heat-treated, but not to FDA-mandated standards
- Raw: which theoretically has not been heat-treated at all
The great cheeses of Europe such as Parmigiano Reggiano and Roquefort are primarily made with raw milk. Cheese can be made with milk that has had the cream skimmed off (Parmigiano Reggiano is made with partially-skimmed milk), or it can be made from whole milk.
Separating the Curds and Whey
Once the milk is ready to go, the first step of cheesemaking is separating the solids from the liquids, also called coagulation. To start, milk is warmed up to the approximate body temperature of the animal. A starter culture blend is then added, which starts to ferment the lactose (milk sugars) into lactic acid, thereby lowering the pH.
There will likely be several kinds of bacteria in the starter culture blend, but the one responsible for fermenting the lactose is called lactic acid bacteria. Other bacteria, called "secondary cultures," maybe in the starter culture blend, but they don't play much of a role in the cheese's development until the ripening process.
Thanks to the lactic acid bacteria, even fresh cheese is very low in lactose, and once the cheese has been aged for more than a few months, the lactose will have virtually disappeared. If someone has an upset stomach after consuming both milk and aged cheese, their bodies are probably intolerant to milk proteins, rather than lactose. Some people find that cow's milk products upset their stomach, but goat's milk or sheep's milk products don't. Everyone is different!
Some fresh cheeses are entirely coagulated through the acidification of the milk. Most cheeses, however, require the addition of an enzyme called rennet to fully coagulate the cheese. Traditional rennet comes from the fourth stomach chamber of a young ruminant animal (usually a byproduct of the veal industry) and is therefore not vegetarian. That said, there are some lab-derived and plant-based alternatives.
Once rennet has coagulated the milk, what was once liquid milk will resemble milk jelly. In order to continue on with cheesemaking, the curds, or milk solids, must be separated from the whey, or liquid. This can happen through a combination of cutting, stirring, heating, and draining.
The curd is usually the star of the show from this point on, though some cheeses like Gjetost or Ricotta are made from whey. Otherwise, whey can be used as fertilizer, sold to protein powder manufacturers, or fed to animals. In Parma, Italy, the leftover whey from making Parmigiano Reggiano is fed to the pigs who will one day become Prosciutto di Parma.
Different Processes for Different Cheeses
Depending on the style of cheese desired, the process varies slightly from here.
If a high-moisture cheese like a Brie is being made, the curd will be kept very loose and wet. The cheesemaker may gently hand-ladle the curds into forms to keep them more intact.
If a dry, more aged style of cheese is being made, the curd will be cut into very small pieces in order to release more whey before the individual curds are formed into a wheel. For a cheese like burrata or mozzarella, the curd is warmed, stretched, and then formed into its final shape. Cheeses made in this style are in the "pasta filata" or "pulled curd" family.
Salt is an important ingredient in cheese and will be added at a slightly different stage by cheese style. Most cheeses soak in brine after the wheel is formed, a gentler way to introduce salt than adding dry salt crystals to the curd pieces. "Dry salting" the curds is typically only done in some cheddars and blues. Some brie-style cheeses, blue cheeses, and "Alpine-style" cheeses like Gruyere are dry salted after being formed into a wheel.
Ripening: Where the Flavor Forms
Next, a cheese ripens. It sounds simple, but actually is the most labor-intensive part of making most cheese. Proper ripening or affinage requires friendly bacteria, a cool, humid climate, and the affineur, or person responsible for ripening cheese, to all work in concert. Thanks to the fermentation process, fats and protein are broken down to unlock new textures and flavors. Secondary cultures also can help shape a cheese's final flavor and texture.
Hard, dry cheeses like Parmigiano Reggiano require more time to ripen. While a brie-style cheese may just ripen for a month or so, the minimum amount of time a true Parmigiano Reggiano can be aged is 12 months, and most are aged around 24 months.
During their short ripening period, brie-style cheeses develop their unique rinds, which drive flavor and texture development. Among cheese professionals, this style of cheese is called a "bloomy rind," referring to the growth of a secondary culture called Penicillium candidum or Penicillium camemberti which sprouts up on the surface of the cheese like dandelion fuzz. The affineur pats down the fuzz and flips the cheese in order to form an even rind.
That rind is what transforms the cheese into the oozy dream we know as Brie. If you've ever cut into a brie-style cheese and seen an oozy halo between the rind and the rest of the cheese (called paste), that is called a creamline. Had the cheese been allowed to ripen further, the creamline would have expanded.
Ammonia is the byproduct of this ripening process. If you buy a brie-style cheese and smell ammonia when you open it at home, that's perfectly normal. Most of the time, letting your cheese sit at room temperature for an hour or so will let the ammonia blow off.
Before a blue cheese is allowed to ripen, the cheesemaker pierces it with stainless steel needles, which exposes a secondary culture called Penicillium roqueforti to oxygen. This allows the mold to grow into the distinctive, spicy blue veins we know and love in blue cheeses like Roquefort.
The affineur tends the cheese until it's ready to be released into distribution channels. From there, it makes its way over land and water, then through the aisles of your local shop until it lands safely onto your plate.