Randy Chandler
Cheese is a beloved snack and ingredient for many, but is it just rotten milk? Well, not exactly. While cheese is indeed made from milk, it undergoes a lot more processing than simply being left to spoil. The process of making cheese involves a series of steps that transform milk into the delicious, creamy product we know and love. The specific steps and techniques used can vary depending on the type of cheese being made, resulting in the wide variety of cheeses available today.
| Characteristics | Values |
|---|---|
| Cheese-making process | Milk is separated into solids and liquids (coagulation). A starter culture blend is added to convert lactose into lactic acid. Rennet, an enzyme, is added to curdle the milk. The curds and whey are separated. Salt is added, and the curds are cut and heated to release more whey. The curds are then pressed into molds and left to age. |
| Cheese as controlled spoilage | Cheese is a form of controlled spoilage of milk, resulting in a more perishable and delicious form of concentrated fat and protein. |
| Bacteria in cheese-making | Bacteria in the starter culture blend ferment lactose into lactic acid. Other secondary cultures may be present but play a role later in the ripening process. |
| Milk source | Milk for cheese typically comes from cows, but can also come from goats, buffalo, sheep, camels, reindeer, and yaks. |
| Health considerations | Pasteurization is a process used to kill pathogens in milk before cheesemaking. Some critics argue that it also kills beneficial bacteria. |
| Cheese varieties | Mozzarella is kneaded like dough, giving it a stringy quality. Swiss cheese is made with bacteria that produce carbon dioxide, creating holes. Limburger cheese gets its strong smell from the same bacteria that cause stinky feet. |
| Homemade cheese | It is possible to make cheese from sour milk at home by warming and separating the milk, straining and draining the mixture, and then chilling the resulting lump to form a block of crumbly fresh cheese. |
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What You'll Learn
Cheese is not simply rotten milk
It is a common misconception that cheese is simply rotten milk. While it is true that cheese is made from milk, the process of turning milk into cheese is far more complex than simply letting milk rot.
Firstly, milk contains two types of proteins: casein and whey. When milk "rots" or goes bad, this is because bacteria in the milk are growing rapidly. However, this is not the same process that turns milk into cheese. To make cheese, a “starter culture” of bacteria is added to fresh milk to convert the lactose into lactic acid. This lowers the pH of the milk. The specific bacteria used in the starter culture will influence how the cheese looks, smells, and tastes.
The next step is to add rennet, an enzyme that causes the milk to curdle. In the past, rennet was obtained from the stomachs of young cows, but today it is usually obtained from bacteria and yeast that have been genetically modified to produce the enzyme. Once the milk has curdled, the curds (milk solids) must be separated from the whey (liquid). This can be done through a combination of cutting, stirring, heating, and draining.
The curds are then cut into smaller pieces, and salt is added. The mixture is heated again to release more whey, which is drained off, leaving clumps of casein. These clumps are then pressed into moulds and left to age for various periods of time. The amount of moisture left in the cheese will depend on the type of cheese being made. For example, a high-moisture cheese like Brie will have a looser, wetter curd.
As we can see, the process of making cheese is much more intricate than simply letting milk rot. It involves specific cultures of bacteria, enzymes, and careful control of temperature and moisture levels. While it is true that cheese is a form of "controlled spoilage" of milk, it is a complex and carefully orchestrated process that results in a delicious and historic food enjoyed by many.
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Bacteria in milk causes it to spoil
Milk is 80 to 90 percent water, depending on the animal it comes from, and it also contains fat, protein, sugar, and minerals. Milk can spoil due to bacteria, and the process of cheesemaking is a controlled spoilage of milk. During this process, friendly bacteria are harnessed, and harmful bacteria, or pathogens, are avoided.
Bacteria in milk cause it to spoil, and this can happen in raw or pasteurized milk. Dairy processing involves pasteurization, commercial sterilization, fermentation, dehydration, refrigeration, and freezing, all of which aim to prevent or control spoilage. However, certain bacterial strains can survive pasteurization and cause spoilage in processed milk. For example, Paenibacillus bacteria are spore-forming bacteria that can cause off-flavors and curdling in dairy products, even after pasteurization.
The spoilage of milk is caused by the growth of fermentative bacteria, particularly when storage temperatures are high enough for psychrotrophs to grow. Psychrotrophic bacteria are of primary importance in cheese spoilage as they produce very active proteolytic and lipolytic enzymes. Spoilage can also occur due to heat-resistant proteinases of psychrotrophic bacteria, which can remain active even after heat treatment.
Several types of bacteria have been identified as causing spoilage in raw and pasteurized milk. In raw milk, Gram-negative bacteria such as Pseudomonas fluorescens biovar I, Ps. fragi, Ps. lundensis, and Ps. fluorescens biovar III are the predominant spoilers. Minor spoilers in raw milk include Enterobacteriaceae spp. and Acinetobacter spp. Pasteurized milk is predominantly spoiled by the same Gram-negative organisms, as well as Bacillus spp., which grow fermentatively in milk.
To prevent spoilage, milk is often pasteurized to kill harmful microbes and pathogens. However, even with pasteurization, some bacteria can survive and cause spoilage. This is why proper storage temperatures and additional processing methods are crucial in preventing spoilage and extending the shelf life of dairy products.
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Starter cultures are added to milk to make cheese
Cheese is a form of controlled spoilage of milk, resulting in a more delicious and less perishable form of concentrated fat and protein. During this process, friendly bacteria are harnessed and harmful bacteria, or pathogens, are avoided.
Starter cultures are essential to the manufacture of many cheese types and are added to milk to start the transformation of milk into cheese. The term 'starter culture' is used to describe the bacteria specially grown to initiate this transformation. Starter cultures are commonly added to the vat by one of three methods: Direct to Vat Inoculation (DVI), bulk starters, and natural methods.
DVI is the most favoured method by many producers as it is easy to use, store, quick, consistent, and convenient. They are sachets of freeze-dried LAB powder that are sprinkled straight onto the milk in the cheese-making vat. However, some argue that the resulting flavour is not as rich or complex. Bulk starters are cultures obtained from farms and now kept alive and managed by different laboratories. They are more difficult to handle for the cheese-maker but can produce a more complex flavour. Prior to the wide use of commercial bought-in starter cultures, natural methods were used, where cheese-makers on farms would use various methods to harness their own population of lactic acid bacteria to acidify the milk.
The primary role of starter cultures is the production of lactic acid from lactose at a predictable and controlled rate. Acid development leads to milk coagulation in acid-coagulated cheeses, a key step in cheesemaking. In addition, creating lactic acid uses up the lactose sugar and milk nutrient resources, making it harder for 'bad' pathogenic and spoilage bacteria to grow. These two factors make it harder for 'bad' bacteria to grow and help preserve the cheese, which is why cheese keeps longer than milk.
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The milk is then separated into curds and whey
Milk is made up of two types of proteins: casein and whey. The process of making cheese involves separating these proteins into curds (solids) and whey (liquid). This process is called coagulation.
To start, milk is warmed up to the approximate body temperature of the animal from which it came. A starter culture blend is then added, which starts to ferment the lactose (milk sugars) into lactic acid, thereby lowering the pH. This blend contains several kinds of bacteria, including lactic acid bacteria and secondary cultures. Lactic acid bacteria are responsible for fermenting the lactose, while secondary cultures play a more significant role in the ripening process.
Once the milk has been adequately coagulated, the curds or milk solids must be separated from the whey or liquid. This can be done through a combination of cutting, stirring, heating, and draining. For example, the whey can be drained off by pouring the mixture into a strainer lined with cheesecloth, leaving clumps of casein behind.
The curds are then further processed to make cheese. They may be cut into smaller pieces, heated to release more whey, and drained again. Salt may be added at this stage. Finally, the curds are pressed into moulds and left to age (dry) for various periods.
The whey, which is a thin, watery liquid, can also be used in various ways. It can be fed to animals, used as fertiliser, or sold to protein powder manufacturers. Some cheeses, like Gjetost or Ricotta, are also made from whey.
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The curds are then pressed into moulds
Cheese is the result of the controlled spoilage of milk, or "milk's leap to immortality". This process results in a more delicious and less perishable form of concentrated fat and protein.
To make cheese, a "'starter culture' of bacteria is added to milk to convert the lactose into lactic acid. Then, an enzyme called rennet is added to curdle the milk. Once the casein has curdled, the whey protein is separated as a thin, watery liquid. The curds are then cut into smaller pieces and heated to release more whey. The additional whey is drained off, leaving clumps of casein.
The moulds used to shape the cheese can be made of a variety of materials, such as plastic or wood. The curds are packed tightly into the moulds and then weighed down to help press out any remaining whey and to ensure the cheese holds its shape. After the cheese has been pressed, it is removed from the mould and then typically brushed with salt to form a rind and improve its flavour.
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Frequently asked questions
Cheese is made from milk that has been treated with bacteria and enzymes to create a controlled spoilage of milk. This process results in a less perishable, more flavourful form of concentrated fat and protein.
To make cheese from spoiled milk, you must first separate the solids from the liquids, or coagulate the milk. This can be done by warming the milk until it separates into solids and a watery liquid. The curds, or milk solids, are then separated from the whey, or liquid. The curds are then cut into smaller pieces, heated, and drained. Salt is added, and the curds are pressed into moulds and left to age.
In the United States, milk used for cheese typically comes from cows. However, in other parts of the world, milk from goats, buffalo, sheep, camels, reindeer, and even yaks can be used to make cheese.
