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🧀 Cheese: milk, microbes and time

Milk is mostly water. Cheese is what is left when you break its protein cage, drain it, salt it and wait for the microbes to work.

5
lessons
~30 min
to learn
🔬 Science
subject
Adults
level
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What you’ll learn

  1. Milk is a suspension waiting for an excuseDescribe milk's composition and explain how casein micelles stay suspended.Milk is mostly water carrying fat droplets and casein clusters whose charged coats keep them apart, and coagulation means removing or neutralising those coats.
  2. The cut: rennet and acidContrast enzymatic and acid coagulation and explain where rennet comes from today.Chymosin cuts the casein coat to give an elastic, ageable curd, while acid neutralises it to give a soft fresh one, and most rennet is now produced by microbes rather than calves.
  3. Everything after that is drainageExplain how curd size, cooking, pressing and salting set a cheese's moisture and therefore its style.Cheese styles are a single continuum of how much water was allowed to stay, set by curd size and pressure, with salt doing four jobs at the end.
  4. Time, and the microbes you inviteExplain proteolysis and lipolysis in ageing and identify the organisms behind blue, bloomy, washed and eyed cheeses.Ageing releases flavour by cutting large molecules into small ones, and every visible feature — crystals, veins, holes, a runny ring — records a specific biological process.
  5. Why cheese exists at allExplain cheese as preservation and describe how place and regulation shape traditional cheeses.Concentrating protein and fat, removing water, acidifying and salting turns a perishable liquid into a food that keeps and travels, and local conditions leave a mark strong enough to be written into law.

Questions this course answers

What does the enzyme in rennet actually do to milk?

Chymosin severs one specific bond in the outer casein protein. Stripped of the charged tails that repelled each other, the micelles link into a gel that traps the water and fat.

Why does cutting the curd into smaller pieces produce a harder cheese?

Curd size sets the surface available for whey to drain through. Rice-sized grains lose far more water than walnut-sized ones, which is the difference between a hard grating cheese and a soft one.

Put the stages of making a hard cheese in order

Set, cut, drain and press, salt and age. Almost every difference between cheese styles is a difference in how far each of those stages is pushed.

Match each cheese feature to what causes it

Every visible feature of an aged cheese is a record of a biological process, and most of them can be read directly off the cut face.

Roughly how many litres of milk go into one kilogram of hard cheese?

About ten litres. Milk is roughly seven-eighths water and cheesemaking discards most of it as whey, so the concentration factor is large.

Complete the sentence about why milk stays liquid

Like charges repel. Removing that repulsion, either by cutting the coats off with rennet or neutralising them with acid, is the whole of coagulation.

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