Heidi is a charming story of a Swiss girl who is raised by her gruff but good-hearted grandfather in a hut high in the Alps. Microeconomics: he uses milk from his two goats to make cheese, which he sells down in town for necessities like nails and sausage and bread. The book mentioned him stirring the milk in a large kettle, and ending up with round cheeses. That makes it look pretty easy.
This got me curious about how Swiss cheese is actually made. I promptly fell down a rabbit-hole of cheese-making technology. It is actually a pretty involved process, where lots can go wrong if you are not on top of it. In a short post here, I can only summarize the steps involved:
1. Prepare the milk
Fresh cow’s milk is filtered and warmed in a large vat. Depending on the cheese and local tradition, the milk may be raw or pasteurized. Traditional Alpine cheeses commonly use raw milk, and some require the use of a copper kettle (more on that below).
2. Add starter cultures and rennet
Lactic-acid bacteria are added to begin converting lactose into lactic acid. Rennet, an enzyme preparation traditionally derived from calf stomachs, is then added to coagulate the milk into a soft gel. Modern producers also add bacteria that operate at high temperatures to convert lactic acid to propionic acid plus carbon dioxide; this reaction makes the holes in Swiss cheese and gives it its nutty flavor. Traditional producers rely on bacteria naturally present in the raw milk and on their equipment and the barn walls. (Side comment, the use of rennet has been known since ancient times; probably some Neolithic folks noted what happened to their milk when they stored it in a calf’s stomach, not having any stainless-steel Yeti bottles on hand.)
3. Cut the curd
The solidified milk is cut into small pieces. This releases whey, the watery portion of the milk.
4. Heat and stir the curds
The curds are stirred while the temperature is raised. This helps expel whey and produces the firm texture characteristic of the cheese.
5. Drain and mold
The whey is separated from the curds, and the curds are transferred into large circular molds, to give the familiar wheel shape.
6. Press the cheese
Pressure compacts the curds and helps expel remaining whey. The curds knit together into a solid wheel.
7. Salt the cheese
The wheel is salted, often by soaking it in brine. Salt adds flavor, draws out moisture, and helps regulate microbial activity during aging.
8. Age and develop the holes
The cheese first undergoes initial ripening and sometimes a warmer stage that encourages propionic-acid bacteria to convert fermentation products into propionic acid, acetic acid, and carbon dioxide. The gas accumulates in openings in the cheese, creating its familiar holes (“eyes”). The wheels are subsequently aged further to develop flavor and texture.
The Role of Copper Cauldrons in Traditional Swiss Cheese Making
It turns out that copper vats serve several different functions. First, copper heats quickly and evenly, and cools just as fast. This lets cheesemakers swing the vat on and off the traditional wood fire with precise temperature control, which is critical during the curd-cooking stage. Second, trace copper ions (typically 5–20 mg/kg) dissolve from the vat into the acidic milk and affect the chemistry in various ways: they bind to milk proteins, remaining in the finished cheese. The copper shifts the balance of bacterial activities, giving cleaner flavor. Copper increases protein breakdown during ripening, which contributes to the rich, nutty flavor. It also, inhibits the release of nasty-smelling hydrogen sulfide.
Modern mass-producers of Swiss cheese try to mimic these chemistries using stainless-steel vats, by adding various chemicals (including sometimes copper). However, regulations require a copper vat for genuine Gruyère, Swiss Emmental, Sbrinz, Raclette, French Comté, and Italian Parmigiano Reggiano.
