Randy Chandler
Cheese is made through a series of processes that transform milk into a product with a longer shelf life, unique flavour, aroma, texture, and colour. This transformation is largely due to the introduction of microorganisms, which are responsible for the fermentation of milk. The microorganisms used in cheese production include bacteria, yeasts, and moulds, with thousands of potential microbes that can be used. These microbes are either introduced deliberately or unintentionally, and they can be native to the milk or added as a starter culture. The type of microbes used depends on the desired cheese variety, as each microbe contributes to the distinct characteristics of the final product.
| Characteristics | Values |
|---|---|
| Microorganisms used in cheese production | Bacteria, yeasts, and moulds |
| Number of microorganisms | Thousands |
| Types of bacteria | Mesophilic, Thermophilic |
| Examples of bacteria | Streptococcus thermophiles, Lactobacillus helveticus, Lactococcus lactis, Leuconostoc mesenteroides, Lactococci, Lactobacilli |
| Function of bacteria | Fermentation, flavour development, texture development, acid production |
| Types of mould | Blue, white, P. camembertii |
| Function of mould | Produce enzymes, break down milk proteins, flavour development |
| Types of yeast | Saccharomyces cerevisiae (baker's yeast) |
| Function of yeast | Feed on lactic acid, neutralise acidity |
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What You'll Learn
Microbes are introduced at every step of the cheese-making process
Microbes are an essential part of the cheese-making process and are introduced at every step, from milk to the final product. The microorganisms found in cheese are responsible for much of the character of the cheese, including its flavour, aroma, texture, and colour.
The first step in making cheese is removing water from milk, which concentrates the milk's protein, fat, and other nutrients, and increases its shelf life. Microbes native to the milk are carried over to the cheese during this step. The milk is then acidified by adding bacteria that convert lactose to lactic acid, lowering the milk's pH and making it inhospitable to spoilage organisms. These bacteria, called "starter cultures", include lactococci and lactobacilli, and are added very early in the cheese-making process.
The milk is then coagulated, and separated into solid curds and liquid whey. The curds are salted, shaped, and left to ripen in a controlled environment. During the ripening process, bacteria break down the proteins, altering the flavour and texture of the cheese. The specific bacteria present during ripening depend on the conditions such as salt concentration and nutrients present. Some cheeses are also pierced during the aging process to encourage the growth of mould.
The final cheese product can contain an extraordinarily high number of microbes, with estimates ranging from thousands to billions. These microbes are generally considered safe to eat and contribute to the unique characteristics of the cheese.
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Microbes determine the flavour, aroma, texture, and colour of the cheese
The unique flavour, aroma, texture, and colour of cheese are determined by the microbes involved in its production. The process of cheese fermentation and flavour formation is a result of complex biochemical reactions driven by the activity of multiple microorganisms. The metabolic activity of microbes produces hundreds of compounds from the protein and fat components in milk that affect the flavour, aroma, texture, and colour of cheese.
The bacteria, moulds, and yeasts that find their way into cheese can be added intentionally by the cheesemaker or they can be introduced unintentionally. The microbes native to the milk will be carried over to the cheese, and as the cheese ages, ambient organisms are also introduced. Microbes are introduced into cheese at every step of the cheese-making process.
The main reaction that occurs when microbes are added to milk is the conversion of lactose to lactic acid, acidifying the milk. This process is known as fermentation and it is how microbes induce flavour development in the cheese. Adjuncts are microbes that are added to encourage flavour development in the cheese. Lactobacillus helveticus, for example, is often added to give cheeses a pleasant sweet flavour and promote the growth of tyrosine crystals.
The smell of cheese is a direct result of the ripening process and the length of time the cheese is given to age. The more extensively the casein and milk fat are broken down, the stronger the aroma of the cheese. The smell of cheese is also influenced by the microbiota associated with a particular variety of cheese, which refines the aroma as the cheese ripens.
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Microbes are added to induce the fermentation process
The process of making cheese involves removing water from milk, which concentrates the milk's protein, fat, and other nutrients, increasing its shelf life. The milk is coagulated, separated into solid curds and liquid whey, and then drained. The curds are then salted, shaped, and left to ripen in a controlled environment.
Microorganisms are used in each step of this process, and they determine the flavour and texture of the final cheese. Microbes are added to induce the fermentation process, which involves the conversion of lactose to lactic acid, acidifying the milk. These microbes are often referred to as "starter cultures". Examples include Lactococci, such as Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris, which are common lactic acid bacteria used to make cheeses like cheddar. Other examples include Lactobacilli, such as Lactobacillus helveticus, which is commonly used in Swiss and alpine cheeses.
The starter culture is a selectively characterized group of bacteria that are intentionally added to the collected milk to induce fermentation. Their primary purpose is to convert lactose in milk into lactic acid, and they also contribute directly to flavour development through the production of enzymes and metabolites. As some of the lactic acid bacteria within the starter culture begin to die, they release enzymes that further break down milk proteins, and these enzymes are an important food source for subsequent generations of microbes.
The activity of the starter culture is particularly important, as the rate and level of acid production contribute significantly to defining the final composition of the cheese. The metabolic activity of microbes produces hundreds of compounds from the protein and fat components in milk that affect the flavour, aroma, texture, and colour of the cheese. The complex flavour characteristics of a cheese typically reflect the activities of several strains and species of microorganisms. For example, the white surface mold of a bloomy rind cheese such as Brie or Camembert is due to a complex ecosystem involving at least four different microbes, including Penicillium camemberti and Geotrichum candidum.
In addition to bacteria, yeasts are also commonly used in the moulding and surface ripening of cheeses, and they are naturally present in many natural rind cheeses. The careful balance of yeast, mould, and bacteria gives rise to natural rinds. Specific moulds are also added by cheesemakers to achieve the desired type of cheese. For instance, the popular mould species Penicillium camemberti is responsible for the nice white lawn on the surfaces of cheeses like Camembert and Brie, and its metabolism is responsible for the characteristic aromas associated with white mould cheeses.
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Microbes are classified as mesophilic or thermophilic
Microorganisms are essential in the production of cheese, contributing to its unique flavour, texture, aroma, and colour. These microbes can be introduced deliberately or unintentionally at every step of the cheese-making process. The two most common types of microbes used in cheese production are mesophilic and thermophilic cultures.
Mesophilic microbes, or mesophiles, thrive at room temperature but die at higher temperatures. They are used to make low-temperature and fresh cheeses. Lactococcus lactis and Leuconostoc mesenteroides are examples of mesophilic species that aid in Cheddar and Gouda production. Mesophilic microbes are also commonly used in Cheddar cheese production, and they are responsible for the acidification of milk by fermenting lactose into lactic acid. This process aids in developing the desired texture and acidity of the cheese. Some mesophilic starters can grow at temperatures as high as 40°C, while others can survive but not grow at 45°C.
Thermophilic microbes, or thermophiles, are used to make longer-aged cheeses that are heated to higher temperatures. These microbes can survive and grow at elevated temperatures, with some even exceeding pasteurization requirements. Streptococcus thermophilus, Lactobacillus helveticus, and Lactobacillus delbrueckii are examples of thermophilic species associated with Swiss and Italian-type cheeses. Thermophilic cultures are commonly used in soft cheeses such as Mozzarella and some Alpine Tomme-style cheeses. In some cheeses that traditionally use mesophilic culture, such as Cheddar, a small amount of thermophilic culture may be added to the blend to work during the aging process.
The choice between using mesophilic or thermophilic cultures depends on the desired type of cheese and the temperature range during the ripening process. If the temperature is up to 90°F, mesophilic culture is recommended, while thermophilic culture is preferred for temperatures between 68-125°F. Both types of cultures can be combined to make certain types of hard cheeses, such as Provolone, Romano, and Parmesan.
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Microbes are killed by pasteurisation
Microorganisms play a crucial role in the unique characteristics of cheese, influencing its flavour, aroma, texture, and colour. These microbes can be introduced at various stages of cheese production, either deliberately or unintentionally. However, not all microbes are desirable, and some can lead to spoilage or contamination. This is where pasteurisation comes into play.
Pasteurisation, named after the French microbiologist Louis Pasteur, is a process of food preservation that involves treating packaged foods, particularly liquids like milk and fruit juices, with mild heat, typically below 100 °C (212 °F). This process effectively eliminates or deactivates unwanted microorganisms, such as bacteria, yeasts, and moulds, that can cause food spoilage or pose health risks. By inactivating these microbes, pasteurisation plays a crucial role in extending the shelf life of dairy products and ensuring food safety.
The process of pasteurisation specifically targets spoilage microbes and pathogens. For example, it kills harmful bacteria such as Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli O157:H7. Additionally, pasteurisation helps prevent diseases caused by pathogens, including tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever. This process is especially important in the dairy industry, where milk provides an excellent medium for microbial growth, and raw milk can be a source of dangerous food-borne diseases if not handled properly.
While pasteurisation is effective in killing or deactivating many microbes, it is important to note that not all spoilage organisms are destroyed. Some bacterial spores can survive the process, and subsequent refrigeration is necessary to prevent their growth. Additionally, pasteurisation might promote the growth of spores, and certain microbial populations may need to be reintroduced to achieve the desired dairy product. Furthermore, thermophilic microorganisms that survive the heating process can attach to the surfaces of equipment, leading to recontamination.
In conclusion, pasteurisation is a critical process in cheese production and the dairy industry as a whole. By killing or deactivating unwanted microorganisms, it ensures food safety, minimises spoilage, and extends the shelf life of dairy products. However, it is important to complement pasteurisation with proper handling, storage, and subsequent refrigeration to prevent contamination and the growth of surviving or thermoduric microbes.
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Frequently asked questions
There is no single answer to this question as it depends on the type of cheese being produced and the production method. A simple, fresh white cheese may only contain microbes of a single species or two, whereas in long-ripened cheeses such as Roquefort, hundreds of different kinds of bacteria and fungi have been detected.
Microorganisms used in cheese production include bacteria, yeasts, and moulds. Examples of bacteria used in cheese production include Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. cremoris, Streptococcus thermophiles, Lactobacillus helveticus, and Lactobacillus delbrueckii ssp. Examples of moulds used in cheese production include Penicillium camemberti, Geotrichum candidum, and Kluyveromyces lactis.
Microorganisms are used in cheese production to induce the fermentation process and develop the flavour, aroma, texture, and colour of the final cheese product.
