Cheese making: from milk to ripened cheese
How cheese is made: rennet or acid coagulation, cutting, cooking, draining, salting and ripening, cheese types, defects, and a Van Slyke yield sum.
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Cheese is one of the oldest ways of preserving milk: concentrating its protein and fat into a form that keeps for weeks, months or years. Thousands of varieties exist, from fresh paneer and cottage cheese to Cheddar, Gouda, Parmigiano-Reggiano, mozzarella, feta, Camembert and Roquefort, yet almost all are made by the same basic steps: coagulate the milk, separate curd from whey, shape and salt the curd, and, for most, ripen it. Small differences in milk, cultures, temperatures, moisture and time create the variety.
Cheese technology is a core topic in dairy science and technology exams, often with yield calculations.
The steps
1. Milk preparation
Milk is checked for quality and antibiotic residues, standardised for its fat-to-casein ratio, and usually pasteurised (some traditional cheeses use raw milk, under strict rules). Calcium chloride is often added to improve coagulation.
2. Starter cultures
Mesophilic (Lactococcus) or thermophilic (Streptococcus thermophilus, lactobacilli) starters produce lactic acid, which helps coagulation, expels whey, controls unwanted bacteria and drives flavour development during ripening.
3. Coagulation
- Rennet coagulation: the enzyme chymosin cuts κ-casein, which stabilises casein micelles, at a specific bond (between phenylalanine 105 and methionine 106). The micelles then aggregate in the presence of calcium to form a gel. Rennet was traditionally extracted from calf stomachs; today most cheese is made with fermentation-produced chymosin made by microorganisms, or with microbial and plant coagulants.
- Acid coagulation: acid alone, from cultures or added acids, coagulates casein at about pH 4.6, as in cottage cheese, quark and cream cheese.
- Acid–heat coagulation: heating milk and adding acid, as in paneer, ricotta and queso blanco.
4. Cutting the curd
The gel is cut into cubes; smaller cubes release more whey and give a drier, harder cheese.
5. Cooking and stirring
Heating the curd (for example to about 38 °C for Cheddar, and up to about 53 to 55 °C for Swiss and Italian hard cheeses) contracts it and expels more whey (syneresis).
6. Draining and texturing
Whey is drained. In Cheddar, slabs of curd are stacked and turned (cheddaring) as acidity rises and the curd develops a fibrous texture, then milled into pieces. In pasta filata cheeses such as mozzarella and provolone, the curd is stretched in hot water.
7. Salting, moulding and pressing
Salt is added to the milled curd (dry salting, as in Cheddar) or the formed cheese is placed in brine (as in Gouda and feta). Salt controls moisture, microbes and enzyme activity and adds flavour. Cheeses are moulded and pressed to form a rind.
8. Ripening
During ripening, enzymes from rennet, milk, starter and secondary microorganisms break down:
- proteins (proteolysis) into peptides and amino acids, softening texture and adding savoury flavours;
- fats (lipolysis), especially important in blue cheeses and some Italian cheeses;
- lactose and lactate (glycolysis).
Secondary cultures create distinctive types: Penicillium roqueforti in blue cheeses; Penicillium camemberti in white-mould cheeses like Camembert and Brie; Propionibacterium producing the eyes of Emmental; and smear bacteria on washed-rind cheeses.
Classifying cheeses
- By moisture: fresh and soft (high moisture), semi-hard, hard and very hard (low moisture).
- By coagulation: rennet, acid, or acid and heat.
- By ripening: unripened (fresh), ripened, mould-ripened (surface or internal).
- By milk: cow, buffalo (mozzarella di bufala), sheep (Roquefort, pecorino, feta), goat.
Processed cheese
Processed cheese is made by grinding natural cheeses, adding emulsifying salts such as sodium citrate and phosphates, and heating and mixing to a smooth, uniform mass, then packing it as slices, blocks or spreads. Emulsifying salts bind calcium and let the casein hold fat in a stable emulsion, giving long shelf life and smooth melting.
Common defects
- Early gas from coliforms or yeasts, and late blowing from Clostridium tyrobutyricum spores (often from poor silage), causing cracks and off-flavours.
- Bitterness from excess proteolysis.
- Too acid or too dry from poorly controlled starter activity or cooking.
- Mould and mite contamination during ripening.
Predicting cheese yield
The Van Slyke formula predicts Cheddar yield from milk composition:
Yield (kg per 100 kg milk) = [(0.93 × F) + (C − 0.1)] × 1.09 ÷ (1 − W)
where F is milk fat (%), C is casein (%), W is the cheese moisture as a fraction, 0.93 is the fraction of fat retained, 0.1 allows for casein lost in whey, and 1.09 accounts for salt and other solids.
Milk with 3.6 per cent fat and 2.5 per cent casein, making Cheddar at 37 per cent moisture:
- (0.93 × 3.6) + (2.5 − 0.1) = 3.348 + 2.4 = 5.748.
- × 1.09 = 6.265.
- ÷ (1 − 0.37) = 6.265 ÷ 0.63 ≈ 9.94 kg of cheese per 100 kg of milk.
Buffalo or sheep milk, with much more fat and casein, gives far higher yields, which is why many traditional cheeses use them.
Key points
- Basic steps: prepare milk, add starter, coagulate, cut, cook, drain, shape, salt, press and ripen.
- Chymosin cuts κ-casein so micelles aggregate; acid coagulates casein at pH 4.6; acid plus heat makes paneer and ricotta.
- Cutting, cooking and salting control moisture and therefore texture and keeping quality.
- Ripening involves proteolysis, lipolysis and glycolysis, plus secondary moulds and bacteria in many types.
- Van Slyke: yield = [(0.93F) + (C − 0.1)] × 1.09 ÷ (1 − W).
What the exams ask
- School-leaving and entrance papers: steps of cheese making and examples of cheese types.
- Degree and research-fellowship entrances: rennet action on κ-casein, acid and acid–heat coagulation, syneresis, cheddaring, salting methods, ripening biochemistry and classification.
- Dairy technology examinations: yield prediction, defects and their control, whey utilisation and quality standards.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
What is the difference between paneer and cottage cheese?
Paneer is made by heating milk and adding acid, giving a firm, unripened cheese that holds its shape when cooked. Cottage cheese is made by acid coagulation of skim milk with cultures and is soft and moist.
Is cheese made with animal rennet?
Some traditional cheeses still use calf rennet, but most cheese worldwide is now made with fermentation-produced chymosin or microbial coagulants, which suit vegetarians.
What happens to the whey?
It is processed into whey protein concentrates, lactose and permeates, used in foods, sports nutrition and animal feed; disposing of it untreated would pollute water.
Sources
- Fox, P. F., Guinee, T. P., Cogan, T. M. and McSweeney, P. L. H. Fundamentals of Cheese Science, 2nd edition. Springer, 2017.
- Walstra, P., Wouters, J. T. M. and Geurts, T. J. Dairy Science and Technology, 2nd edition. CRC Press, 2006.
- Van Slyke, L. L. and Price, W. V. Cheese. Orange Judd, 1949.
- Codex Alimentarius Commission. General Standard for Cheese (CXS 283-1978).
- McSweeney, P. L. H. "Biochemistry of cheese ripening." International Journal of Dairy Technology 57, 127–144 (2004).
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