Andy Montoya
Cheese is a dairy product made through the fermentation of milk. The process of making cheese through fermentation involves several steps, including preparing and inoculating milk with bacteria, curdling the milk, cutting and cooking the curd, draining the whey, salting, pressing, and ripening. This process transforms the milk proteins, carbohydrates, and fats, resulting in the characteristic flavour and texture of cheese. The type of bacteria and fermentation conditions influence the final product, and the production of cheese through fermentation has allowed dairy products to be preserved and stored at room temperature for extended periods.
How is Cheese Made by Fermentation?
| Characteristics | Values |
|---|---|
| Basic Ingredients | Milk, microorganisms, rennet, and salt |
| Milk Preparation | Milk is boiled, cooled down, and cheese culture is added |
| Fermentation Process | Microorganisms convert lactose to lactic acid, causing milk to curdle and separate into curds and whey |
| Curd Treatment | Cut, cooked, salted, pressed, and ripened |
| Ripening/Aging | Cheese is aged in controlled environments like caves or climate-controlled buildings to develop flavour and texture |
| Types of Cheese | Hard and soft cheeses, e.g., cheddar, feta, cottage cheese, cream cheese |
| Function of Fermentation | Allows dairy to be stored at room temperature for long periods, acts as a form of food preservation |
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What You'll Learn
Fermenting microorganisms and rennet
The first step in the fermentation process involves preparing and inoculating milk with lactic-acid-producing bacteria, also known as fermenting microorganisms, and rennet. The lactic bacteria convert the sugar (lactose) in the milk to lactic acid. The type of microorganisms used depends on the variety of cheese and the production process. The lactic acid and rennet cause the milk to curdle, separating the curds (made of milk solids, fats, and proteins) and whey (mostly water).
Rennet is an enzymatic preparation that contains a number of proteolytic (protein-degrading) enzymes. It is a binding agent that acts as a coagulant, causing the milk to curdle and clump up into curds. Rennet is traditionally derived from the abomasum of calves, but microbial and vegan alternatives are now available. The use of animal rennet has decreased over time, with less than 5% of cheese in the United States still being made using it. This shift is partly due to the limited availability of mammalian stomachs and the demand for vegetarian and kosher options.
Microbial rennet is produced by the fermentation of certain species of moulds, such as Rhizomucor miehei, which generate protein-splitting enzymes necessary for cheese-making. This type of rennet is suitable for vegetarians and those keeping kosher. Fermentation-produced chymosin (FPC) is another alternative that is identical to animal-derived chymosin but is produced through genetic engineering. FPC is widely used in industrial cheesemaking due to its commercial viability, higher yield, better curd texture, and reduced bitterness.
The choice of rennet can impact the flavour and characteristics of the cheese. For example, some cheese makers prefer calf-derived rennet for aged cheddars to achieve their desired flavour profile. On the other hand, vegetable rennet from certain plants, such as thistles or cardoons, may lead to bitter and undesirable flavours in cow's milk cheeses.
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Curdling milk
Milk curdling is a crucial step in the process of cheese-making. It involves separating the milk solids, fats, and proteins (curds) from the water (whey). Curdling is achieved by adding lactic acid bacteria and rennet to the milk, causing it to clump together and precipitate out of solution.
The milk is first inoculated with lactic acid-producing bacteria, which convert the lactose in milk to lactic acid. This process, known as fermentation, releases energy by consuming sugar in the absence of oxygen. The lactic acid produced causes the milk to curdle. Additionally, rennet, an enzymatic preparation containing proteolytic enzymes, is usually added to promote curdling. The type of bacteria and the amount of rennet used depend on the variety of cheese being made and the production process.
During curdling, the milk protein casein clumps together, forming a solid or gel-like mass. The curds are then cut into small cubes, and in some cases, heated to force out more whey and alter the taste of the final product. The amount of whey released during curdling affects the texture and flavour of the cheese, with harder cheeses requiring more whey removal.
After cutting and heating, the curds undergo draining or dipping to remove the whey. Salt is typically added to the curds at this stage, enhancing flavour, inhibiting undesirable microorganisms, and further drawing out moisture. The curds are then pressed and salted again before being sent for aging. The aging period, also known as ripening, allows enzymes and bacteria to modify proteins, fats, and sugars, intensifying flavour and transforming texture.
The curdling process is essential to cheese-making as it separates the desired solids from the liquid whey. By controlling the curdling process, cheesemakers can produce specific types and qualities of cheese, ensuring the final product has the desired characteristics.
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Separating curds and whey
The process of separating curds and whey is an important step in cheese-making. Curds are made of milk solids, fats, and proteins, while whey is mostly water.
To separate the curds and whey, the milk is first inoculated with lactic acid-producing bacteria and rennet, which promote curdling. The bacteria convert the lactose in the milk to lactic acid, causing the milk to curdle and separate into curds and whey. The curds are then allowed to soak until the lactic acid bacteria reach the right concentration, after which the whey is drained off.
The curds can then be further processed by pressing, salting, and mixing with secondary microflora before being sent for aging. The whey, which is a byproduct of the cheese-making process, can also be used in various other applications, such as in the production of ricotta cheese or as a protein supplement.
The separation of curds and whey is a crucial step in the cheese-making process as it helps to remove excess moisture and consolidate the milk solids, fats, and proteins that give cheese its characteristic texture and flavour. The removal of whey also helps to concentrate the bacteria and enzymes in the curds, which is essential for the aging and ripening process that gives cheese its distinct characteristics.
In some cheese-making methods, such as the traditional method of making Kazak cheese, the curds are placed in a canvas bag and hung outdoors to further remove moisture and solidify into fresh cheese. This step also involves the separation of curds and whey, as the whey is allowed to drain out of the canvas bag, leaving behind the solidified curds that will be further processed into cheese.
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Aging and ripening
Aging, also known as ripening, is one of the most important steps in the cheese-making process. It allows cheese to develop its full flavour, aroma, and texture. The process is characterized by a series of complex physical, chemical, and microbiological changes that incorporate bacteria, enzymes, and environmental contaminants.
The ripening time varies depending on the type of cheese, ranging from one month for Brie to a year or more for sharp cheddar. The speed of these reactions is determined by temperature and humidity conditions, as well as the moisture content of the cheese. The majority of cheese is ripened, except for fresh cheese, which is ready for sale as soon as it is made. Fresh cheeses typically have a mild, soft, and/or creamy flavour. Examples of fresh cheeses include cottage cheese, cream cheese, ricotta, farmer's cheese, and most mozzarella.
The ripening process is influenced by a variety of factors, including the microflora, the curd, and the enzymatic process. The most important agents in this process include bacteria, enzymes, and physical conditions in the curing room. The bacteria and enzymes play a major role in flavour formation and the rate of cheese ripening. The degree of protein decomposition, or proteolysis, also affects both the flavour and consistency of the final cheese.
To accelerate the ripening process, an elevated ripening temperature can be used. This method is commonly employed to control the rate of flavour development in hard cheeses. Additionally, specific enzymes can be added to the cheese milk or curd to speed up ripening, such as proteinases, peptidases, lipases, and esterases.
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Pasteurization
There are two main types of heat treatment used in pasteurization: Low Temperature Long Hold (LTLH) and High Temperature Short Hold (HTSH). In LTLH, the milk is heated to a temperature of up to 149° F for 30 to 40 minutes. This method is preferred for cheese-making as certain enzymes and bacteria will survive, which are necessary for the fermentation process. HTSH, on the other hand, involves heating the milk to a higher temperature of up to 174° F for a shorter duration of 22 to 40 seconds. This method kills all enzymes and almost all bacteria, leaving nothing active to transform milk into cheese.
The decision to use pasteurized or raw milk in cheese-making depends on various factors. Raw milk, or unpasteurized milk, is milk that has not undergone the pasteurization process. Some cheesemakers prefer using raw milk as they believe it creates more flavorful and healthful cheeses. The complexity of flavors in raw milk cheese is often preferred by cheese connoisseurs. Additionally, traditional European cheeses like Parmigiano Reggiano, Camembert, and some types of Brie are required by France's Appellation d'origine contrôlée (AOC) to be made with raw milk.
However, there are food safety concerns associated with raw milk cheese. In the United States, the Food and Drug Administration (FDA) has implemented regulations to protect consumers from potentially harmful bacteria in raw milk. Raw milk cheese cannot be sold in the US unless it has been aged for a minimum of 60 days at a temperature of at least 35° F. After this aging period, the acids and salts in the cheese naturally prevent the growth of dangerous bacteria such as Listeria, Salmonella, and E. coli.
On the other hand, pasteurized milk cheese is considered safer due to the destruction of harmful pathogens during the heat treatment process. It is important to note that pasteurization may also impact the flavor and texture of the resulting cheese. Cheeses made from pasteurized milk tend to ripen more slowly and may have a less intense flavor compared to their raw milk counterparts. Additionally, mandatory pasteurization of milk for cheesemaking could adversely affect certain varieties of cheese, such as Swiss and hard Italian cheeses, which rely on native milk enzymes and microflora for their traditional flavor.
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Frequently asked questions
The first step in the fermentation process happens when the milk is inoculated with lactic acid bacteria, our primary microflora, and rennet in a vat.
The bacteria feed on the lactose in the milk, producing lactic acid as a byproduct. This process is often called aging, but it is actually a type of fermentation.
The essential steps in cheese fermentation are: preparing and inoculating the milk with lactic-acid–producing bacteria, curdling the milk, cutting the curd, shrinking the curd (by cooking), draining or dipping the whey, salting, pressing, and ripening.
