Milk is the most perishable useful food there is. It also arrives, if you keep an animal or know someone who does, in a daily quantity that nobody can drink.
Yoghurt and soft cheese are the two simplest ways of turning today's surplus into something that keeps days rather than hours, and both need nothing but heat, time and a starter.
Why bother
- It extends milk from about 2 days to 1 to 2 weeks, or longer for a drained cheese.
- The culture renews itself. Keep a spoonful back and you never need to buy another starter.
- It needs no equipment. A pan, a thermometer and something insulated.
- It is more digestible than milk for many people, because the bacteria consume much of the lactose.
- Whey is a by-product, not waste. It goes into bread, soup, animal feed, or as the starter for a vegetable ferment.
The two temperatures
The scald does two jobs, and the second is the one people miss. Pasteurising is obvious. The less obvious effect is that holding milk at 82°C or above changes the whey proteins so they can join the curd structure, and that is what makes the difference between thick yoghurt and thin yoghurt. Milk merely warmed to 43°C and cultured will set, and it will set loose and watery. A longer hold at the top of the range gives a thicker result, which is why Greek-style yoghurts start with an extended scald.
The cooling step is where batches are lost. Lactobacillus bulgaricus and Streptococcus thermophilus are killed above roughly 46°C. Adding the starter to milk that is still too hot kills it, and nothing happens for the next five hours. Use a thermometer. The old test of holding a clean finger in for ten seconds works, and a thermometer works better.
Making yoghurt
- Heat the milk to 82 to 85°C, stirring so it does not catch. Hold it there for 10 to 20 minutes; longer gives thicker yoghurt.
- Cool to 43°C. Standing the pan in cold water speeds it up considerably.
- Stir in the starter: 2 to 3 tablespoons of live yoghurt per litre, or a sachet of freeze-dried culture. Mix a little milk into the starter first to loosen it, then stir that back in, so it disperses evenly.
- Keep it at 40 to 45°C for 4 to 5 hours. This is the only difficulty and it is not much of one. Options: a vacuum flask; the pan wrapped in towels in a warm cupboard; an oven with only the light on; a cool box with a jar of hot water; wrapped in a blanket next to a stove.
- Do not disturb it while it sets. Moving or stirring breaks the curd and gives a grainy, weeping result.
- Check at 4 hours. It should have set like a soft custard and pull cleanly from the side of the pot. Longer gives a sharper, more sour yoghurt.
- Refrigerate, or keep as cool as you can. It firms up further as it chills.
Troubleshooting:
| Problem | Cause |
|---|---|
| Did not set at all | Milk too hot when the starter went in, or dead starter |
| Set very thin | Scald skipped or too short, or incubation too cool |
| Grainy or separated | Incubated too hot, or disturbed while setting |
| Too sour | Incubated too long |
| Watery layer on top | Normal. That is whey. Pour it off or stir it in |
| Pink, orange or fuzzy growth | Contamination. Discard, and scald the equipment |
Keeping the culture going
Keep 2 to 3 tablespoons of each batch back as the starter for the next. In principle this runs indefinitely.
In practice the culture drifts: the balance between the two organisms shifts with each generation, and after roughly 10 to 20 batches it usually gets slower, thinner or more sour. Start again from a fresh live yoghurt or a new sachet when that happens.
Keep a dried backup. Spread a little yoghurt thinly on clean greaseproof paper, dry it somewhere warm but under 45°C, and store the flakes airtight in the dark. It will restart a culture months later, and it costs nothing to make. In a long emergency this is the difference between having yoghurt and not.
Soft cheese from yoghurt
The simplest cheese there is, and it needs no rennet.
- Line a sieve with muslin and set it over a bowl.
- Tip in the yoghurt.
- Let it drain in a cool place: 2 to 4 hours for a thick Greek-style yoghurt, 12 to 24 hours for a spreadable curd cheese, 24 to 48 hours with a light weight on top for something firm enough to slice.
- Salt it to taste, roughly 1 to 2% by weight, which also improves keeping.
- Add herbs, garlic or pepper, or roll it in them.
- Refrigerate. It keeps a week or so, longer if salted harder and kept cold.
Keep the whey. It is genuinely useful: in bread instead of water, in soup, as the liquid for a vegetable ferment, or fed to hens and pigs.
Acid-set cheese, the fastest route
If you have milk and no culture at all, an acid-set cheese takes twenty minutes. This is paneer, queso fresco and the traditional crowdie.
- Heat milk to 85 to 90°C.
- Take off the heat and stir in acid: about 1 to 2 tablespoons of lemon juice or vinegar per litre.
- Wait a minute or two. The curds separate from the greenish whey. Add a little more acid if separation is incomplete.
- Strain through muslin.
- Rinse briefly with cool water if you used vinegar and do not want the flavour.
- Salt, press if you want it firm.
It does not melt or stretch, and it fries and crumbles beautifully. It also uses milk that is on the turn but not yet off, which is exactly the situation this page exists for.
Raw milk
If milk goes off before you get to it, do not culture it and hope. Soured raw milk has been colonised by whatever was in it, which is not the same as being cultured by organisms you chose. Use it for the hens, or discard it.