Vol. XIV · Fermentation Plate 6 of 11cheese, rennet, chymosin, curd, whey, casein, yield, moisture, ripening, cheddar, paneer, Van SlykeMT

Cheese.

Ten litres of milk make about a kilogram of cheddar, or two of a soft fresh cheese. The difference is mostly water left in.

Milk is about 87 % water, 3–4 % fat, 2.5 % casein, 0.6 % whey proteins and 4.8 % lactose. Cheese-making gathers the casein and fat and lets most of the rest go. Two ways set the curd. Rennet, whose enzyme chymosin snips the protective κ-casein hairs from the casein micelles, lets them join with calcium into an elastic gel at the milk's own pH, near 32 °C: cheddar, gouda, parmesan. Acid — from lactic bacteria or added lemon or vinegar to hot milk — takes casein to its isoelectric point (XIV.5): fresh cheeses, paneer, ricotta-like curds, and the Chinese 乳扇.

Then the cheesemaker controls water. Cutting the curd small, stirring, heating and pressing expel more whey and make a firmer, drier cheese that keeps; leaving the curd in large pieces and unpressed keeps it soft and moist. Salt draws out more whey, slows spoilage and steers ripening, during which enzymes and microbes break proteins and fats into the flavours of aged cheese over weeks to years. The workshop works out the yield.

Below: the weight of cheese from the milk you choose against the cheese's moisture (the Van Slyke yield formula), with typical moisture of familiar cheeses marked, and the yield at your settings.

What you will learn
Workshop
Van Slyke yield: kg of cheese per 100 kg of milk = (0.93 F + C − 0.1) × 1.09 / (1 − W), with F the milk's fat %, C its casein % and W the cheese's moisture fraction (1.09 allows for salt and other solids). Milk taken as 1.03 kg per litre. Typical moistures: parmesan about 30 %, cheddar 37 %, gouda 42 %, camembert 52 %, fresh cheeses 60–80 %.

Casein, fat and the water left in

Ten litres of whole milk give about 1.06 kg of cheddar at 37 % moisture, 0.95 kg of a parmesan-style cheese at 30 % and 1.90 kg of a fresh cheese at 65 %: the same casein and fat, holding different amounts of water. Fat counts as well as casein: the same ten litres of milk skimmed to 1 % fat make only 0.59 kg of cheddar-type cheese. Cheese-makers are paid by the casein and fat in their milk for this reason.

At home the easiest cheeses are acid-set: heat milk to about 90 °C, stir in lemon juice or vinegar until the curd separates from a yellowish whey, drain and press for paneer or 奶豆腐-style fresh cheese. Rennet cheeses need a starter culture, careful temperatures and, for aged cheese, a cool, humid place for weeks. Raw-milk cheeses carry Listeria and other risks (XII.4); the at-risk groups should choose pasteurised hard cheeses.

At the stove

Heat a litre of whole milk to just below the boil, take it off the heat and stir in two tablespoons of lemon juice. When it separates, pour it through a cloth-lined sieve, squeeze, and press under a weight for an hour: paneer. Weigh it and compare with the milk.

Chymosin for cheese-making once came only from the stomachs of milk-fed calves; since 1990 most has been made by fermentation with microbes carrying the calf gene, the first enzyme from a genetically modified organism approved for food.

Terms

Rennet
An enzyme preparation, chiefly chymosin, that sets milk into a curd.
Curd
The gel of casein and fat that becomes cheese.
Whey
The liquid left when the curd forms.
Ripening
Ageing, during which enzymes and microbes develop a cheese's flavour and texture.
Cheese gathers casein and fat by rennet or acid; the water left in decides soft or hard and the yield, about a tenth of the milk for cheddar.

Sources

  1. Van Slyke and Price, Cheese (1949): yield = (0.93 F + C − 0.1) × 1.09 / (1 − W), with F and C the fat and casein percentages of the milk and W the moisture fraction of the cheese; the classic estimate of cheddar yield.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.