From milk to cheese, in nine steps.

HTST pasteurisation (72 °C for 15 s) inactivates pathogens and most native enzymes, including alkaline phosphatase — the standard test for adequate heating. Harsher heat denatures whey proteins such as β-lactoglobulin, which then associate with κ-casein and impair rennet coagulation; that is one reason cheese milk is not heated harder. Milk is often standardised to a target casein-to-fat ratio, which fixes the fat-in-dry-matter of the finished cheese.

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Mesophilic starters (Lactococcus lactis) suit cheeses made around 30 °C; thermophilic starters (Streptococcus thermophilus with Lactobacillus helveticus or Lb. delbrueckii) survive the high cooking temperatures of Alpine and grana-type cheeses. Acid production dissolves colloidal calcium phosphate from the micelles, changing curd texture and meltability. In blue and bloomy cheeses, mould spores (Penicillium roqueforti, P. camemberti) are often added to the milk at this stage.

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Casein micelles are kept apart by κ-casein, whose C-terminal “hairs” (the caseinomacropeptide) give steric and electrostatic stabilisation. Chymosin specifically hydrolyses the Phe105–Met106 bond of κ-casein; once about 85% of it is cleaved, the para-casein micelles aggregate in the presence of Ca²⁺ and build a gel network. Acid-set cheeses take another route: as the pH approaches casein’s isoelectric point (pH 4.6), the micelles aggregate without rennet.

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Cutting starts syneresis — the gel’s contraction and expulsion of whey. Its rate depends on surface area, temperature, pH and stirring. Cut too early and fat and fines are lost to the whey; too late and the firm gel shatters. Cheesemakers judge the moment by firmness, traditionally by a “clean break”.

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Cooking temperature is a primary control of moisture, and so of the cheese’s later texture and ripening speed. High scald temperatures also select the microbes: they inactivate much of the mesophilic flora and partly denature the coagulant — which is why long-aged cooked cheeses rely on thermophilic starters and on plasmin for proteolysis.

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Stretching works only in a narrow pH window: as acid dissolves calcium phosphate, para-casein becomes plastic enough to be heated and drawn into aligned fibres, typically around pH 5.2–5.3. Cheddaring lets the curd mat, lose whey and gain acidity before milling and dry salting. The drained whey still carries whey protein and lactose; heated and acidified, it becomes whey cheeses such as ricotta and lor.

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Pressing closes the openings between grains and expels residual whey; the curd must still be warm and plastic enough to fuse. Protected cheeses are often marked in the mould: Parmigiano Reggiano’s dotted rind lettering and its casein plaque with a unique code are applied at this stage.

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Salt diffuses inward slowly — in brine-salted wheels it can take weeks to even out — and lowers water activity. Salt-in-moisture is a key quality measure: it governs starter activity, the survival of non-starter bacteria and the balance between bitterness and savoury flavour from proteolysis. Feta and the Turkish white cheeses are not just salted in brine; they mature and are sold in it.

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Proteolysis is the master process: residual coagulant and plasmin cut caseins into large peptides, which starter and non-starter lactic acid bacteria break into small peptides and free amino acids — precursors of savoury and nutty flavours. Lipolysis frees fatty acids; it is strongest in blue cheeses, where Penicillium roqueforti lipases lead to methyl ketones. Ripening agents mark the families: P. roqueforti in blues, P. camemberti on bloomy rinds, Brevibacterium linens and other smear bacteria on washed rinds, and Propionibacterium freudenreichii, whose CO₂ forms the eyes of Emmental-type cheeses. Minimum ripening times are set in each PDO specification.

Sources [1] [3] · minimums: EU PDO specifications (eAmbrosia)