Why Are Some Cheeses Soft and Other Cheeses Firm? Ask Paul

Cheese starts out as milk, which consists of protein, sugar, fat, minerals, and almost 90 percent water. The first essential step in turning milk into cheese is to form curds. Adding enzymes and/or acid to milk will cause the milk’s casein proteins, which are naturally suspended in the liquid, to unravel and cling to each other, coagulating into solid curds.

The remaining liquid—the whey—is now drained off the curds. How this step is done is crucial for the final texture of the cheese. 

In the case of a soft cheese like Brie, the curds are delicately moved from their initial vat into a container where they’re allowed to drain slowly over a period of hours. This approach retains a lot of moisture in the cheese. The greater the moisture content in the final product, the softer it is.

Cheeses destined to be firm, on the other hand, get a rougher treatment. After the curds form, they’re cut into smaller pieces by sweeping specialized knives through the vat, in order to allow the curds to release more of the whey trapped inside them. The smaller the pieces, the more moisture can be released. Adding salt and heating the vat then causes the curds to tighten up and squeeze out liquid—the higher the temperature, the more liquid is released.

The curds, drained of liquid, now start to fuse together into a single piece, which will become the cheese.

The drained, interconnected protein curd is placed in cheesecloth-wrapped forms and pressed into shape. A soft cheese gets only the gentlest squeeze, while firmer cheeses are subjected to many tons of pressure, forcing out as much water as possible.

The next step is aging, which also affects the texture of the cheese. Some cheeses are sealed in wax or plastic before they’re aged, which prevents any more moisture from evaporating. Others, such as Parmigiano Reggiano, are encouraged to dry out and harden over the course of years of aging, although they form a natural rind that slows down the drying process.

In some cheeses, like Brie, the aging process softens rather than hardens the cheese. Minerals that lend strength to the protein structure are able to gradually leave the protein, in part because there’s enough water for them to move around. This causes the structure to weaken; enzymes can further break down the protein structure, which is the final step that can turn a soft cheese into a runny one.

Anyone who’s luxuriated in a buttery high-fat soft cheese, a so-called double- or triple-crème cheese like St. André or mascarpone, knows the spreadable richness associated with these, which have as much as 40 percent fat, comparable to heavy cream. That’s because they’re made with cream in addition to milk, and all that delicious fat remains in the final product.

Triple- and double-crèmes are the exception, though. Most commonly, an ounce of soft cheese contains less fat than an ounce of a firm cheese, because the soft cheese contains so much more water. So a regular Brie might contain 25 percent fat (and almost 50 percent water), while a cheddar comes in at 35 percent fat and 36 percent water. Parmigiano contains a surprising 30 percent water (hard to detect because it’s snugly held by the protein mesh) and 30 percent fat.