Cheese is made from milk, a coagulant (usually rennet), bacterial cultures, and salt. These four ingredients, combined with time and temperature control, transform liquid milk into the hundreds of cheese varieties found around the world. The type of milk, the coagulant used, and the specific bacteria involved all shape the final flavor, texture, and nutritional profile.
Milk: The Starting Point
Every cheese begins with milk, and the animal it comes from makes a big difference. Cow’s milk is the most common base worldwide, containing roughly 3 to 4 percent fat and 3.5 percent protein. Goat’s milk has a similar composition to cow’s milk but produces cheese with a tangier, more distinctive flavor. Sheep’s milk is richer in both fat and protein, which is why cheeses like Pecorino Romano and Roquefort have such dense, intense character. Buffalo milk has the highest fat content of the group, about double that of cow’s milk, and its high calcium-to-protein ratio makes it especially well suited to cheesemaking. That’s why fresh mozzarella made from buffalo milk has a creamier, softer texture than the cow’s milk version.
What matters most in the milk is casein, the primary protein. Casein is what eventually becomes the solid cheese. The fat trapped alongside it contributes richness and mouthfeel. Lactose, the natural sugar in milk, serves as fuel for the bacteria that drive fermentation.
Bacterial Cultures and Fermentation
Starter cultures are specific strains of bacteria added to the milk early in the process. Their job is straightforward: consume lactose and convert it into lactic acid. This acidification does several things at once. It lowers the pH of the milk, which helps the curd form and expel moisture. It inhibits the growth of harmful bacteria. And it acts as a natural preservative that allows cheese to last far longer than fresh milk.
But these bacteria do more than just produce acid. During the weeks or months of aging, their enzymes break down proteins and fats inside the cheese, generating the complex flavors that distinguish a sharp cheddar from a mild one. Some strains produce carbon dioxide, creating the holes in Swiss-style cheeses. Others generate compounds like diacetyl, which gives butter and certain cheeses their characteristic aroma. The specific combination of bacterial strains is one of the biggest reasons two cheeses made from identical milk can taste completely different.
Rennet and How Milk Becomes Solid
Rennet is the enzyme that physically transforms liquid milk into a semisolid gel. It works by causing casein proteins to link together into a mesh-like network, trapping water and fat inside. This gel is then cut into curds, which are separated from the liquid whey.
Traditional rennet comes from the stomach lining of young calves, goats, or lambs, where the enzyme naturally helps the animal digest its mother’s milk. Today, about one-third of all cheese produced worldwide uses microbial rennet instead, sourced from specific molds. Microbial rennet is cheaper to produce, available in unlimited quantities, and carries no risk of disease transmission. There’s also a lab-produced version called recombinant chymosin, which is genetically identical to the calf enzyme but made through fermentation, making it suitable for vegetarians despite its animal-identical structure.
Plant-based coagulants exist too. Artichokes, nettles, and cardoon thistle all contain enzymes that can curdle milk. Cheeses from Spain and Portugal have a long tradition of using cardoon thistle as a coagulant. The tradeoff is that plant enzymes tend to break down proteins more aggressively, which can lower the cheese yield and sometimes create bitter flavors.
Some fresh cheeses skip rennet entirely and use direct acid, like vinegar or lemon juice, to curdle the milk. Paneer and ricotta are common examples of this approach.
What Salt Does in Cheese
Salt is the final core ingredient, and it plays a more complex role than just adding flavor. When salt is applied to fresh cheese curds, it draws out residual whey through osmosis, lowering the moisture content. Less moisture means a firmer texture and a longer shelf life. Salt also lowers the water activity inside the cheese, which directly controls how fast bacteria can grow during aging. Too little salt leads to excessive bacterial activity, which can make the cheese overly soft, gummy, or prone to spoilage.
In blue cheeses like Roquefort, salt concentration is especially important. The mold responsible for the blue veining needs at least 1 percent salt to germinate properly. Reducing salt in surface-ripened cheeses can disrupt the entire microbial community on the rind, leading to off-flavors or spoilage. Salt content, in other words, is one of the cheesemaker’s primary tools for steering the aging process.
Common Additives Beyond the Basics
Many cheeses include a few additional ingredients. Calcium chloride is frequently added to pasteurized milk because pasteurization disrupts some of the calcium bonds in casein. Adding a small amount back shortens the time it takes for rennet to coagulate the milk and produces a firmer curd. Annatto, a natural pigment derived from the seeds of the achiote tree, gives cheeses like cheddar, Colby, and Red Leicester their orange or yellow color. Without it, most cow’s milk cheese would be pale white to light yellow, depending on the season and the cow’s diet.
Nutritional Profile
Cheese concentrates the protein, fat, and minerals from milk into a much denser package. One ounce of hard cheese (roughly the size of your thumb) contains about 120 calories, 8 grams of protein, 6 grams of saturated fat, and 180 milligrams of calcium. Soft cheeses distribute those nutrients differently: a half-cup of full-fat cottage cheese has about 120 calories but 14 grams of protein, less saturated fat, and 80 milligrams of calcium. Cheese is also a notable source of phosphorus, vitamin B12, and vitamin A.
Plant-Based Cheese Alternatives
Vegan cheeses take a fundamentally different approach since they contain no animal milk at all. An analysis of 245 plant-based cheese products found the most common bases were coconut oil combined with food starches like potato, tapioca, or corn starch (accounting for the largest share), followed by cashew and coconut blends, pure cashew, oats, almonds, and soy. These products are made by creating an emulsion of plant oils, plant proteins, water, emulsifiers, stabilizers, and natural flavorings.
The nutritional differences are significant. Coconut oil-based products, which dominate the market, tend to be high in saturated fat (4 to 7 grams per serving) and contain close to zero protein. Cashew and almond-based alternatives are much lower in saturated fat (0 to 1 gram per serving) and offer more protein, though still less than dairy cheese. Tofu-based alternatives come closest to dairy cheese in protein content, with roughly 5 grams per 30-gram serving. None of these alternatives naturally match the calcium or B12 content of dairy cheese unless fortified.