Four ingredients turn milk into cheese: rennet, a bacterial culture, an acid and salt. Rennet and acid are the two that actually coagulate the milk, splitting it into solid curds and liquid whey; cultures ripen and flavour cheeses that are going to be aged; salt seasons, firms the curd and does quiet preservation work. Fresh cheeses need a coagulant and salt, sometimes an acid as well, and no culture at all, which is why a first ricotta can be made and eaten inside an hour. Here is what each one is doing, and which of them you actually need for the cheese in front of you.
What does rennet do?
Rennet is an enzyme. Dropped into warm milk, it goes to work on the milk proteins, which lose the thing that was keeping them apart and begin to link into a soft gel. Nothing is added or taken away: the milk simply stops behaving like a liquid.
Traditionally the enzyme came from the stomach lining of a calf. The rennet in our kits is a vegetarian one, a microbial coagulant produced by Rhizomucor miehei, so it is suitable for vegetarians and does the same job on the same milk.
Rennet is the fussiest of the four, though only mildly. Dissolve it in cool, non-chlorinated water (cooled boiled or bottled water is ideal), mix it fresh just before you use it, and stir it gently but thoroughly through the milk. Chlorine straight from the tap can weaken it, and so can age, which is why a rennet-set cheese that refuses to set almost always points at one of three things: UHT milk, the wrong temperature, or tired rennet mixed with tap water.
You know rennet has worked when you get a clean break. Dip a clean knife or a finger in at an angle and lift: if the curd splits cleanly and the whey filling the gap runs clear rather than milky, it is ready to cut. Still soft and cloudy means give it a few more minutes.
What does the acid do, and when do you use it instead?
Acid gets to the same destination by a different road. Lower the pH of warm milk far enough and the proteins clump together on their own, no enzyme required. That is the whole principle behind the oldest and simplest cheeses in the world.
Citric acid is the acid in our kits, and it is what makes ricotta, paneer and queso blanco possible in an afternoon. These are acid-set cheeses: no rennet, very forgiving, and a good place to start. The quick mozzarella method uses citric acid too, alongside rennet, which is what lets you go from cold milk to a warm stretched ball in about an hour rather than overnight.
Acid-set curds behave differently from rennet-set ones. They form almost at once, they are softer, and they are more easily overworked. Too much acid is a real fault: it gives you a cheese that is rubbery or oddly crumbly, so follow the quantities in the recipe rather than eyeballing it.
Do you need a culture?
For fresh cheese, no. Mesophilic and thermophilic cultures are bacterial starters, and they belong to ripened and aged cheeses, where they work slowly over weeks and months to build flavour, acidity and texture. Our kit recipes are either acid-set or set with fresh rennet, and they do not need them.
That is worth saying plainly, because a lot of cheese making writing treats cultures as compulsory and leaves beginners convinced they are missing an ingredient. They are not. If you go on to aged cheeses later, you will buy cultures separately and choose the right one for the style, and by then you will know exactly what you want from it.
What does the salt do?
More than you would expect. Salt seasons, obviously, but it also draws out moisture, firms the curd and slows the microbes that would otherwise shorten the life of a fresh cheese. Cut the salt right back in a halloumi and you have made a trade, not a saving: a low-salt halloumi should be eaten within two days.
The salt in the kits is cheese salt: non-iodised, and without the anti-caking agents that ordinary table salt carries. For most cheeses you sprinkle it over the drained curds, mix gently and let it sit a few minutes to absorb. Halloumi and feta styles are brined instead, in salt water, and the brine is single-use, so make it, use it and pour it away.
And the milk itself?
The fifth ingredient, and the one people get wrong most often. Use fresh, full-fat pasteurised cow's milk; standard supermarket whole milk works beautifully. Never use UHT or ultra-pasteurised milk, which simply will not curdle, and avoid lactose-free milk. For chevre, use goat's milk and expect much smaller, softer curds than cow's milk gives.
Your pan matters too. Use a non-reactive one, which in practice means stainless steel. Cast iron, aluminium and copper all react with the acid going into the milk and can spoil both the flavour and the look of the finished cheese.
Which of the four come in a kit?
Three of them, plus the kit that spares you the shopping list. Our Cheese Making Kit, Cheeses of the World includes vegetarian rennet, citric acid and cheese salt along with a thermometer, moulds and cheesecloth, and covers ten fresh cheeses including mozzarella, halloumi, paneer, ricotta, mascarpone, chevre and burrata. You add fresh whole milk, a stainless pan, a slotted spoon and a colander.
If you want the widest run of recipes, the Grand Cheese Making Kit carries forty recipes, from ricotta, cream cheese and paneer through to burrata and pressed, brined and flavoured cheeses such as herb halloumi, with seven seasonings alongside the same rennet, citric acid and cheese salt. Both make fresh cheeses rather than aged ones, and both are built so the first cheese happens on the first evening.
Cheese ingredients FAQs
Do I need both rennet and acid to make cheese?
No. Some cheeses are set with rennet, some with acid alone, and a few, including the quick mozzarella method, use both. The recipe tells you which, and the kits include both.
Is the rennet in the kits suitable for vegetarians?
Yes. It is a microbial coagulant produced by Rhizomucor miehei rather than an animal rennet, so vegetarians can eat the cheese you make with it.
Why will my milk not curdle?
Almost always UHT or ultra-pasteurised milk, the wrong temperature when the rennet or acid went in, or old rennet mixed with chlorinated tap water. Fix those three and it sets.
Can I use ordinary table salt instead of cheese salt?
At a push, use a plain non-iodised salt with no anti-caking agents. Iodine and additives can interfere with flavour and with cultures, which is why the kits include a proper cheese salt.
Can these four ingredients make cheddar?
Not on their own. Aged and ripened cheeses need bacterial cultures and months of controlled storage. Our kits make fresh cheeses, which is where the technique is learned.
Fancy making your first curds this week? Have a look at our cheese making kits.
