Milk, lemon juice, thirty minutes. The fastest way to understand cheesemaking with your hands rather than by reading about it.
What you need
A litre (roughly a quart) of milk, two or three tablespoons of lemon juice or vinegar, a pinch of salt, a sieve and a piece of muslin. Nothing special. If you have no muslin, a clean handkerchief or thin tea towel works, as do several stacked coffee filters. A heavy-based pan is worth having, since a thin one heats unevenly and the milk catches. A thermometer is convenient but optional — there is a way to judge by eye, described below.
Choosing the milk is half the job
This is where most failures come from. First, whole milk beats reduced-fat milk decisively: low-fat gives a smaller yield and a drier result. Second, and more important, is how it was pasteurised. Ultra-heat-treated milk has already had its proteins altered and will not curdle properly however much acid you add. A great deal of supermarket milk is UHT, so this is worth checking — a carton marked as gently or traditionally pasteurised gives noticeably better results. Expect 200 to 300 grams (7 to 10 oz) of cheese from a litre.
The method
Add a little salt to the milk and heat it to 85°C (185°F). Without a thermometer, look for this: a ring of small bubbles around the edge of the pan and steam clearly rising, but no rolling boil. Take it off the heat, add the lemon juice, stir three or four times, and leave it alone for 15 to 20 minutes. Covering the pan slows the cooling and improves the set. When it has separated into white curds and clear yellow liquid, pour it into a muslin-lined sieve and let it drain. Draining time sets the texture: fifteen minutes gives something moist, an hour gives something spreadable.
Do not stir, do not boil
Failures divide into two. Keep stirring after adding the acid and the curds that were forming break apart again into pieces too small for the muslin to catch — most of the cheese simply drains away. Boil it hard and the proteins tighten too much, giving something stiff and dry. Once the acid is in, take your hands off and wait. Impatience is the only real enemy. And when you do stir, make it two or three slow passes, just enough to distribute the acid.
When it refuses to curdle
If twenty minutes have passed and the pan still holds cloudy milk, there is either not enough acid or not enough heat. Add another tablespoon of lemon juice and wait five more minutes; if that fails, return it to a low flame and lift the temperature slightly. If neither works, the milk was almost certainly ultra-pasteurised — no technique fixes that, only a different carton next time. The opposite problem, curds too fine to catch in the sieve, is solved by stirring less and waiting longer.
Lemon and vinegar give different results
Both work, but not identically. Lemon juice leaves a faint citrus note that suits desserts and fruit. Vinegar contributes no aroma but can leave a slightly sour finish. For cheese destined for cooking, vinegar is cheaper and perfectly good. Either way, rinsing the drained curds briefly under water removes much of the acidity — though it removes the lemon character too, so skip the rinse if that is what you wanted.
Strictly speaking, this is not ricotta
Real ricotta is made by reheating the whey left over from making another cheese; the name literally means recooked, and it was a thrifty way of getting a second yield from a by-product. What you make at home from milk is milk set with acid — closer to a plain fresh curd. The taste and texture come remarkably close, but they are not the same thing, and it is better to know that going in. It is also safer not to call it ricotta in front of an Italian.
The real thing is this:
What to do with it
Spread it on bread while still warm and pour over honey or olive oil — it will be the best thing you eat that day. Freshly made, its aroma is not comparable to anything sold in a tub. It goes into pasta and lasagne, or mix it with sugar and lemon zest for dessert. It is an unaged fresh cheese, so eat it within two or three days. Store it covered, and lay a sheet of kitchen roll underneath, because it keeps releasing a little liquid.
The drained liquid is an ingredient too
The yellow liquid in the bowl beneath the sieve is whey, and it still holds protein and minerals — do not pour it away. Use it in place of water in bread or pancake batter for better flavour, or as a base for soup. Some people put it in smoothies. Plain, it is a little bland, but lemon and honey make it drinkable. Dairies never threw it out either; they made a second cheese from it. Using it twice at home is closer to the original practice than binning it.
Going one step further
Once this feels routine, the next stage is rennet-set cheese. Rennet and starter cultures are easy to buy online. Unlike acid-set curd, the result is springy, and cutting and draining it takes you towards mozzarella or paneer. Anything requiring ripening is a much harder ask at home, since it needs months of steady temperature and humidity. Setting and draining is enough to be worth doing. Even that much makes the language on a cheese label suddenly legible.
The next one to attempt: