Citric acid curdles milk. Stirred into milk that has been warmed to the right temperature, it lowers the pH until the proteins stop repelling one another and clump together into curds, leaving the whey behind. That is the whole job, and it is why a ricotta can be made from scratch in well under an hour with no rennet, no cultures and no waiting. Citric acid is included in our cheese kits alongside vegetarian rennet and cheese salt, and it is the ingredient behind the fastest and most forgiving recipes in the booklet.
How does citric acid turn milk into curds?
Milk proteins stay suspended in milk because they carry a charge that keeps them apart. Drop the pH far enough and that charge neutralises, so the proteins find each other and gather into a solid mass. Warm milk does this more readily than cold, which is why every acid-set recipe starts with a temperature.
Rennet reaches the same destination differently, by using an enzyme to snip away the part of the protein that was doing the repelling. The two routes give noticeably different curds. An acid-set curd forms almost at once and is softer and more granular; a rennet-set curd forms slowly into a smooth gel that you can cut into neat cubes.
Citric acid is simply a convenient, consistent, dry form of the acid. Lemon juice and vinegar will curdle milk too, but their strength varies from bottle to bottle and both carry flavour into the cheese. Measured citric acid gives you the same result every time and tastes of nothing in particular, which is what you want when the cheese is meant to taste of milk.
Which cheeses use citric acid?
Three groups, and they cover a lot of ground.
- Ricotta. The easiest cheese there is, and a perfect first go. Heat, add acid, and gentle curds form almost immediately. Do not over-stir, and drain to taste: less draining for creamy, more for firm.
- Paneer and queso blanco. Acid-set, no rennet, and very forgiving. Press them firmly so they hold together for frying or for cubing into curries and salads.
- Quick mozzarella. This one uses citric acid and rennet together. The acid brings the milk to the right chemistry fast, the rennet sets it, and the curds can then be heated and stretched the same afternoon rather than after an overnight ferment.
Mascarpone sits alongside these as another acid-set make, though it is made from fresh double cream rather than milk. Expect tiny curds rather than ricotta-style ones, drain it slowly in a cloth-lined sieve overnight, and do not be alarmed if you collect only a couple of tablespoons of whey.
Our Cheese Making Kit, Cheeses of the World includes the citric acid, vegetarian rennet and cheese salt along with a thermometer, moulds and cheesecloth, and covers ten fresh cheeses including mozzarella, halloumi, paneer, ricotta, mascarpone, chevre and burrata.
How much citric acid should you use?
Exactly what the recipe says, weighed or measured rather than guessed, because this is the ingredient where more is emphatically not better.
Too much acid is one of the commonest faults in home cheese making and it shows up in two ways. A cheese that comes out rubbery and tough has usually been overheated, overworked or over-acidified. A cheese that crumbles when you try to slice it has often had too much acid as well, sometimes combined with curds cut too small and drained too hard.
Dissolve the citric acid in a little cool water before it goes into the milk, so it disperses evenly instead of hitting one patch hard. Stir it through, then work to the recipe's temperature and timings. If something goes wrong, change one thing next time rather than three, because acid, temperature and handling all pull on the same result.
What else does citric acid do in the kitchen?
In wine making it is used to sharpen a country wine, adjusting the acidity of a finished batch a little at a time. In cheese making it has no such role after the set: once the curds have formed, the acid has done everything it is going to do.
It is also worth knowing what it does not do. Citric acid is not a preservative in a fresh cheese, so an acid-set cheese is still a fridge item with a short life, typically a few days to a week, sealed and cold. It does not replace salt, which is doing separate work on flavour, texture and keeping quality. And it is not a substitute for rennet in a recipe written around rennet, because the curd it produces behaves differently under a knife and under heat.
How should you store it?
Undemanding, happily. Citric acid is a stable dry ingredient: keep it sealed, dry and away from direct sunlight and it will sit there quite contentedly. Reseal what you open and it stays usable for a long time, so you can spread the recipes in a kit over weeks or months rather than racing through them.
The rennet is the ingredient with a clock on it. Because it is an active coagulant, it is the reason to use a cheese kit before the best before date printed on the box rather than long afterwards, and the reason to dissolve it in cool, non-chlorinated water just before use.
Every ingredient is listed on the pack; if you have an allergy question, email hello@sandyleaffarm.com before ordering.
Citric acid FAQs
Can I use lemon juice instead of citric acid?
It will curdle milk, but strength varies between lemons and bottles and it carries its own flavour. Measured citric acid gives a more consistent set and a cleaner tasting cheese.
Does citric acid make cheese taste sour?
Used at the quantity in the recipe, no. It tastes of very little in the finished cheese. A noticeably sharp result usually means too much went in.
Which cheeses need no rennet at all?
Ricotta, paneer and queso blanco are set with acid alone, and mascarpone is made the same way from double cream. They are the most forgiving cheeses to start with.
Why is my acid-set cheese rubbery or crumbly?
Usually too much acid, or curds that were overheated, overworked or drained too hard. Stick to the recipe quantities and temperatures and handle the curds gently.
Is citric acid included in the cheese kits?
Yes. Our cheese kits include citric acid alongside vegetarian rennet and cheese salt, so you only need to buy fresh whole milk, never UHT.
Fancy a bowl of homemade ricotta tonight? See our cheese making kits.
