Cheese is one of the oldest prepared foods in the world, and at its heart it's remarkably simple: it's a way of turning milk into something that keeps, but the journey from a churn of fresh milk to a wheel of mature cheddar involves some science and a surprising amount of craft.
This article explains how cheese is made from start to finish, what it's actually made of and the science of why milk turns into cheese. Whether you're simply curious or thinking about making your own, you'll find the full picture here.
How Is Cheese Made? The Short Version
Cheese is made by curdling milk so that it separates into solids (curds) and liquid (whey). The curds are then drained, salted, shaped and usually aged to develop flavour and texture. That's the whole process in a very short sentence.
The curdling is triggered by two additions - a bacterial starter culture, which sours the milk and rennet, an enzyme that makes the milk proteins clump together. Almost every cheese in the world follows this same basic path. What makes them different is the countless small decisions made along the way - which milk, how much the curd is cut, how long it's cooked, how it's salted and how long it's left to age.
What Is Cheese Made Of? The Four Core Ingredients
Traditional cheese is made from just four ingredients. That's it, despite the enormous variety of cheeses, the ingredient list is short and simple.
1. Milk - The foundation of all cheese, usually from cows, but also from goats, sheep or buffalo. The type of milk has a huge effect on the final cheese. Sheep's milk is richer and higher in fat, goat's milk has a distinctive tang. Around 10 litres of milk typically goes into 1kg of hard cheese which is why cheese concentrates so much flavour and nutrition.
2. Starter cultures - These are beneficial bacteria added to the milk. They ferment the natural sugar in milk (lactose) into lactic acid, which sours the milk and begins the process of turning it into cheese. Different cultures produce different flavours which is one reason cheeses vary so much.
3. Rennet - An enzyme (traditionally taken from the stomach of young calves, though vegetarian versions are now widespread) that causes the milk to coagulate into a solid gel. Rennet is what makes the curds form quickly and firmly.
4. Salt - Added towards the end, salt does several jobs - it seasons the cheese, draws out excess moisture and acts as a preservative by slowing the growth of unwanted bacteria.
Some cheeses add a little more - annatto (a natural plant dye) to make cheeses like Red Leicester orange, or specific moulds like Penicillium for blue and soft-ripened cheeses. But the core of almost every natural cheese is those four ingredients. As the Encyclopaedia Britannica notes, the entire process begins with just milk, microorganisms, rennet and salt.
How Is Cheese Made, Step by Step
Here's the full process, using a traditional hard cheese like cheddar as the example. Softer cheeses skip or shorten some of the later stages.
1. Preparing the Milk
The milk is first checked for quality and usually pasteurised - gently heated to kill harmful bacteria. It may also be standardised, which means adjusting the fat-to-protein ratio to get a consistent result. Some traditional cheeses are made with raw (unpasteurised) milk, which many people believe gives a more complex flavour.
2. Adding Starter Cultures
The prepared milk is warmed and the starter cultures are stirred in. Over the next while, these bacteria get to work converting lactose into lactic acid, gradually souring the milk and dropping its pH. This acidification is essential. It sets up the conditions for the milk to coagulate and it begins developing the cheese's eventual flavour.
3. Adding Rennet (Coagulation)
Next, rennet is added. Within a short time the milk transforms from a liquid into a soft, wobbly gel with a texture a bit like a set yoghurt or a panna cotta. This is coagulation or the moment milk genuinely becomes cheese-in-progress. (Some fresh cheeses skip the rennet and rely on acid alone to curdle the milk, which is why they're softer and more crumbly.)
4. Cutting the Curd
The set gel is then cut with cheese knives into small cubes. This is a crucial step, because cutting releases the whey trapped inside the curd. The size of the cut determines the final texture - the smaller the curds are cut, the more whey escapes, and the harder and drier the finished cheese will be. A hard cheese like Parmesan is cut into tiny, rice-sized grains; a soft cheese is cut much larger, or not at all.
5. Cooking and Stirring
The cut curds are gently heated ("scalded") and stirred. For cheddar, the temperature is slowly raised to around 38 - 39°C. The heat and movement encourage the curds to firm up and expel yet more whey, shrinking as they go. The more the curds are cooked, the drier and firmer the cheese.
6. Draining the Whey
The whey, now a greenish-yellow liquid, is drained off, leaving behind a mat of solid curd. The whey isn't wasted: it's used to make ricotta, protein powders, and animal feed. At this point the curd has gone from liquid milk to a solid, rubbery mass.
7. Cheddaring, Milling and Salting
This stage is specific to cheddar and is where the cheese gets its name. In cheddaring, the mat of curd is cut into slabs, which are then stacked, turned, and re-stacked over one to two hours. This presses out more whey and develops the characteristic dense, layered texture.
The slabs are then milled - cut or torn into small pieces and salted by mixing salt directly through the curds. (Many other cheeses are salted differently, by soaking the finished cheese in a salt brine instead.)
8. Shaping and Pressing
The salted curds are packed into moulds and pressed, often overnight. Pressing forces out any remaining whey and fuses the curds into a single solid block or wheel, giving the cheese its final shape. Traditional truckles are pressed into their distinctive cylindrical form at this stage, then often bound in cloth or coated in wax.
9. Ageing (Maturation)
Finally, the cheese is aged - anywhere from a few weeks for a mild cheese to several years for a vintage. During ageing, the cheese loses moisture and its cultures and enzymes slowly break down proteins and fats, developing flavour and complexity. This is where a bland young curd becomes a sharp, characterful cheese. For more on how ageing changes the result, see our guide to mild vs mature vs extra mature cheddar.
From curd to your kitchen: every cheese in our range goes through this same craft process before it reaches you. Browse our cheese wedges and traditional waxed truckles — made the traditional way from quality British milk, with nothing more than milk, cultures, rennet, and salt.
The Science: Why Does Milk Turn Into Cheese?
It's worth understanding the clever bit at the centre of all this, because it explains everything else.
Milk is mostly water, with proteins, fats, sugars, and minerals suspended in it. The key protein is casein. In fresh milk, casein molecules float around separately because they repel one another - a bit like magnets pushing apart - which keeps the milk liquid.
Rennet contains an enzyme (chymosin) that snips off the part of the casein molecule responsible for that repulsion. Once that happens, the casein proteins can suddenly stick together, trapping the fat and forming a solid gel. That gel is the curd. The watery liquid left behind, containing most of the lactose and some proteins, is the whey.
The starter cultures help by acidifying the milk, which makes the whole coagulation happen more reliably and starts building flavour. So in essence: cultures sour the milk, rennet solidifies it, and everything after that is about controlling moisture and developing flavour. Every technique in cheesemaking is a variation on those simple principles.
Why Are There So Many Different Cheeses?
If almost all cheese starts from the same four ingredients and the same basic process, why is a feta so different from a cheddar, or a Brie from a Parmesan? The answer is that small changes at each stage compound into enormous differences. The main variables are:
The milk - Cow, goat, sheep, or buffalo and whether it's raw or pasteurised, full-fat or standardised.
The cultures - Different bacterial strains produce different acids, aromas, and flavours. Specific moulds create blue veining or bloomy rinds.
How the curd is handled - How finely it's cut, how hot it's cooked, and how much whey is removed all determine whether the cheese is soft and moist or hard and dry.
Salting and shaping - Dry-salted or brined, pressed hard or left loose, bound in cloth or waxed.
Ageing. A few weeks versus a few years, in conditions ranging from cool damp caves to controlled stores.
Multiply all those choices together and you get the thousands of distinct cheeses made around the world.
Is Cheese Suitable for Vegetarians? The Rennet Question
This is one of the most common questions about how cheese is made, and it's worth answering clearly.
Traditional rennet is animal-derived - it comes from the stomach lining of young calves. This means cheese made with traditional rennet is not strictly vegetarian, which surprises many people.
However, the majority of cheese sold in UK supermarkets today is made with vegetarian rennet, produced either from microbial or fungal sources or through fermentation. These non-animal rennets do the same job - coagulating the milk - without using any part of an animal. Cheeses made this way are suitable for vegetarians and are usually labelled as such.
If being vegetarian matters to you, check the label: it will normally state "suitable for vegetarians" or specify vegetarian rennet. A few traditional and protected cheeses (such as authentic Parmigiano-Reggiano and some traditional cheddars) are still made with animal rennet. For a cheese-free alternative entirely, see our guide to what vegan cheese is made of.