Randy Chandler
Cheese is a beloved food for many people around the world, but the process of how it is made from cow's milk is not as well known. The first step in cheese-making is collecting milk from dairy farms, which is then sent to a cheese plant for quality and purity testing. Once the milk passes these tests, it is filtered, standardized, and pasteurized to kill any harmful bacteria. At this stage, cheesemakers add starter cultures, which are good bacteria that feed on lactose sugar in the milk and produce lactic acid. This process of fermentation contributes to the development of flavour, texture, and preservation of the final cheese product. The addition of rennet causes the milk to gel and curdle, separating into curds (solids) and whey (liquid). The curds are then cut, stirred, and heated to release more whey, and salt is added to enhance flavour. The curds are pressed into moulds to form the desired shape and consistency, and the cheese is then aged to further develop its unique characteristics.
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What You'll Learn
Milk collection and quality testing
At the cheese plant, cheesemakers carefully inspect the milk to ensure it meets stringent quality and purity standards. They take samples of the milk to perform thorough tests, verifying that it is safe and suitable for cheese production. This step is crucial as it lays the foundation for the final product's consistency and safety.
Once the milk passes the quality tests, it undergoes standardization. This process involves adjusting the levels of fat, cream, or protein in the milk. Standardization is essential because cheesemakers need to start with a consistent base milk to ensure their cheese has a uniform texture and taste across batches.
After standardization, the milk is pasteurized. Pasteurization is a critical step in eliminating harmful bacteria that may be present in raw milk. By killing these dangerous microorganisms, the process ensures the safety of the milk for consumption and subsequent cheese production.
Following pasteurization, beneficial bacteria, known as "starter cultures," are introduced into the milk. These starter cultures contain living bacteria that initiate the transformation of lactose, the milk's natural sugar, into lactic acid. This step is pivotal in the cheese-making process as it influences the development of flavour, preservation, and curdling.
The specific type of starter culture chosen depends on the desired cheese variety, as different cultures produce distinct flavours and textures. For instance, Swiss cheese employs a particular culture that generates carbon dioxide during lactose digestion, resulting in the characteristic holes in the final product. Similarly, the notorious Limburger cheese derives its potent odour from the same bacteria responsible for stinky feet, Brevibacterium linens.
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Milk standardisation and pasteurisation
Milk Standardisation
Standardisation of milk controls its composition, particularly the fat-in-dry-matter ratio, which helps maximise cheese yield and maintain quality. This is achieved by varying the fat content to reach a defined casein-to-fat ratio. Standardisation is crucial as it ensures the cheese has a consistent taste, texture, and appearance across different batches.
Milk Pasteurisation
Pasteurisation is the process of heating milk to a specific temperature for a certain period, killing harmful microorganisms and improving hygienic quality. The most common method is high-temperature short-time (HTST) pasteurisation, where milk is heated to 72°C for 15 seconds, destroying bacteria such as Salmonella, Listeria, and E. coli. This method is preferred by large-scale commercial cheesemakers due to its efficiency and cost-effectiveness.
However, pasteurisation can have negative effects on cheesemaking. For instance, it can damage the natural flora in raw milk, which is essential for cheesemaking. An alternative method is low-temperature long-time (LTLT) pasteurisation, which heats milk to 63°C for 30 minutes, causing less harm to the milk's bacteria and potentially improving cheesemaking results.
While pasteurisation is a standard practice in dairy production, some cheeses are still made with raw milk, which has not been treated or pasteurised. Raw milk cheese is typically produced on a small scale, and the milk may be thermised to prolong its shelf life before being fully pasteurised for cheesemaking.
In summary, milk standardisation and pasteurisation are critical steps in the transformation of milk into cheese, ensuring the safety, consistency, and quality of the final product.
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Adding bacteria and rennet
After milk is collected from dairy farms, it is taken to a cheese plant for quality and purity testing. Once it passes, the milk is filtered and standardised, and then pasteurised to kill any dangerous bacteria. At this stage, good bacteria or "starter cultures" are added to the milk.
Starter cultures contain living bacteria that feed on the lactose sugar in milk, turning it into lactic acid. This process helps with curdling, preservation and flavour development. Different types of starter cultures are used to create different types of cheese. For example, Swiss cheese uses one type of culture, while Brie and Blue use others.
Rennet is then added to the mixture. Rennet causes the milk to gel, similar to yoghurt, before the curds (the solids) separate from the whey (the liquid). The amount of rennet and time needed for it to separate into curds varies from cheese to cheese. Rennet is now typically obtained from bacteria and yeast that have been genetically modified to make the enzyme, though in the past it was obtained from the stomachs of young cows.
Once the mixture starts to gel, cheesemakers cut it, which allows the whey to come out. Drier cheeses are often cut more to form smaller curds, so more moisture is released. The curds are then stirred and heated to release even more whey.
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Curdling and cutting
The curdling process involves the conversion of milk to a solid or gel-like structure known as curd, which traps fat, bacteria, calcium, phosphate, and other particulates. The remaining liquid, known as whey, is watery and contains proteins, carbohydrates, and minerals. Curdling is facilitated by the addition of lactic acid-producing bacteria and rennet, which contains the protease enzyme chymosin. The type of bacteria and the amount of acid and rennet used depend on the desired variety of cheese and the production process.
The curds are then cut into smaller pieces to initiate moisture loss and create a drier cheese. This process is known as "whey expulsion" or "syneresis". The amount of moisture lost depends on the surface area of the newly formed curd particles. To cut the curds, cheesemakers use a cheese "harp" or cheese "knives", which are devices made up of parallel knife blades and/or wires. The harp/knives are inserted into the vat of cheese and drawn along the curd mass to form curd cubes. This process can be automated using motorized knives for larger-scale operations. However, for some cheeses like ricotta, simply stirring the coagulated milk is enough to break up the curd particles.
The size of the curd particles depends on the desired cheese variety. For example, Grana-style cheeses like Parmigiano-Reggiano start with small rice-sized curd particles, while higher-moisture cheeses like Brie have larger curd particle sizes. After cutting, the curds are usually allowed to rest in a "healing" step before being "cooked". During the cooking process, the curds are heated and stirred, resulting in additional moisture loss.
For some hard cheeses, higher temperatures of 35-55 °C (95-131 °F) are used to force more whey out of the cut curd and change the taste of the final product. These higher temperatures affect the bacterial culture and milk chemistry, and the type of bacteria used must be able to survive this step.
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Draining, moulding and ageing
Draining, moulding, and ageing are crucial steps in the cheese-making process. After coagulation and heating, the whey is drained from the vat, leaving solid curd chunks behind. The size of the chunks depends on the cut of the curd. Draining removes all the whey, resulting in an extensive mat of curd. Some cheesemakers let the whey drain naturally, while others use moulds and presses to facilitate the process. Compression is sometimes used to release more whey by compressing the curd. This process, known as cheddaring, involves stacking individual slabs of curd after cutting them into sections.
Once the whey is drained, the curd is pressed into moulds. The mould can be in the form of a basket or a hoop. A basket mould has one open end, while a hoop mould has no bottom and wraps around the sides. The ground curd mixture is packed into the mould and left to solidify for a fixed period. Moulds are typically rectangular or round.
Ageing is the final step in cheese-making. It involves leaving the cheese to dry and harden for various periods, from a few days to several years. A controlled, cool environment is ideal for ageing, and the temperature and humidity must be carefully monitored. The cheese should be checked regularly, and if it starts to feel too dry, it can be rubbed with olive or coconut oil. Unwanted mould can be removed with a clean rag dipped in white vinegar.
The length of the ageing process depends on the type of cheese being made. Soft ripened and high-moisture cheeses, for example, continue to drain for several days, and the moisture build-up must be closely monitored. These cheeses should be stored in containers that allow them to breathe and prevent the bottom from becoming too moist. The containers should be opened frequently to exchange the gases from the ripening cheese with fresh air.
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Frequently asked questions
The first step in making cheese from cow's milk is to collect milk from dairy farms and bring it to a cheese plant.
Once the milk is collected, cheesemakers check the milk and take samples to ensure it passes quality and purity tests. After the milk passes, it is filtered, standardised, and pasteurised.
After pasteurisation, good bacteria or "starter cultures" are added to the milk. The starter cultures ferment the lactose, the milk's natural sugar, into lactic acid, which helps with curdling, preservation, and flavour development.
