Cheese

Cheese is milk whose protein has been curdled, drained of its whey and often salted and ripened, so that it keeps far longer than fresh milk. Milk-fat residues in perforated Neolithic pots show that farmers in Europe were making it more than 7,000 years ago.

What it is

Cheese is a solid food made from milk by curdling its protein and draining off the watery part, the whey. Fresh cheeses are eaten within days; hard cheeses are pressed, salted and ripened for months or years. Either way, most of the water leaves, and with it much of the lactose, the milk sugar that many adults digest poorly.

The plate follows a farmhouse cheese of the eighteenth century through its stages: curd cut in a copper vat over the fire, the wire harp that cut it, a cloth-lined mould, a screw press and the shelves where the wheels ripen.

How it works

Milk is mostly water holding fat droplets, lactose and proteins. About four fifths of the protein in cow’s milk is casein, which floats in tiny clusters called micelles. Each micelle carries a hairy outer layer of one casein, kappa-casein, that keeps the clusters apart.

Cutting the curd: the smaller the cubes, the more whey runs out and the harder the cheese.

Rennet, traditionally taken from the stomach of a young calf, contains the enzyme chymosin. It cuts kappa-casein at one precise point and shaves off the hairy layer. Helped by the calcium in the milk, the bare micelles then stick together into a soft gel, the curd, which holds the fat inside it. Cheesemakers usually add rennet to milk at about 30 to 32 °C. Acid can also curdle milk, often helped by heat: paneer is made by adding lemon juice or citric acid to hot milk.

Once the gel is firm, the maker cuts it into cubes. Whey seeps out of every cut face. Stirring and gentle heating squeeze out more, and the size of the cubes decides how dry the cheese will be. The curd is then gathered in moulds and pressed, salted on the surface or in brine, and left to ripen. During ripening, bacteria and enzymes break proteins and fats into smaller molecules that give flavour and change the texture. Salt draws water out of the surface, slows unwanted microbes and helps form a rind.

How to build it

The simplest cheese to make at home is paneer, curdled by heat and acid and eaten fresh. You need 2 litres of pasteurised whole cow’s milk, about 5 g of citric acid dissolved in 250 ml of water (or the strained juice of two lemons), a heavy pot, a thermometer, a colander, cheesecloth, a board and a weight of 2 to 3 kg.

Heat the milk. Bring the milk to 85 to 90 °C, stirring so it does not catch on the bottom, then take it off the heat and let it cool to about 70 °C. Curdling much hotter makes a hard, dry cheese; much cooler leaves it wet.

Curdle it. Pour in the acid little by little, stirring gently, until white curds separate and the whey turns clear and greenish-yellow. You may not need all of it. Leave the pot still for ten minutes.

Drain and press. Line the colander with cheesecloth, pour in the curds and let the whey run off. Fold the cloth over, set the board and the weight on top and press for 30 to 60 minutes, until the block holds together.

Chill and store. Cut the block into pieces and soak them in iced water for an hour or two to firm them. Keep the paneer in the refrigerator at 4 °C or below and eat it within three days. Two litres of cow’s milk give about 350 g.

Pressed rennet cheeses that ripen for weeks need a measured starter, checks of acidity at each stage and a cellar kept at the right temperature and humidity. Learn them from a complete, tested recipe or a course before trying.

Safety. Use pasteurised milk: raw milk can carry Listeria, E. coli and other dangerous bacteria, and soft raw-milk cheeses are a known source of listeriosis, a serious risk in pregnancy. Hot milk scalds and boils over easily, so keep children away from the pot. Clean every tool, chill the cheese as soon as it is made, and do not rely on smell or appearance to judge safety: throw away any cheese kept too long, too warm, or that smells or looks wrong.

History and evolution

A Neolithic pottery sieve of the kind that held milk fats in Kuyavia, Poland: probably a cheese strainer.

Most adults in the first farming communities could not digest lactose, although children could. Draining off the whey removes most of the lactose from cheese, and in yogurt bacteria break down part of it. On the Dalmatian coast of Croatia, milk residues appear in pottery about 7,700 years ago, and residues of fermented dairy, soft cheese or yogurt, about 7,200 years ago.

In Kuyavia, in central Poland, a team led by Mélanie Salque of the University of Bristol analysed 50 fragments from 34 perforated pots of the first farmers of central Europe, about 7,000 to 7,500 years old, and found abundant milk fats. No molecule is unique to cheese, but straining curd from whey is the obvious use for such sieves, and the 2012 study counts them as the oldest direct evidence of cheesemaking.

The round eyes of some Alpine cheeses are bubbles of carbon dioxide made by bacteria during ripening.

The oldest surviving cheese itself is about 3,600 years old, on mummies of the Xiaohe cemetery in Xinjiang. The Roman writer Columella, around 65 CE, described rennet curdling, pressing, salting and ageing much as they are practised now.

Medieval monasteries kept and refined many cheeses, and records of Roquefort at the abbey of Conques go back to 1070. In the United States cheese stayed a farm product until 1851, when Jesse Williams in Oneida County, New York, began making it from the pooled milk of neighbouring farms, the first cheese factory in the United States. Commercial rennet extract appeared in the 1860s and 1870s, and pure bacterial cultures followed, which made production far more consistent. Most rennet used today is chymosin made by microbes.