Andy Montoya
Cheese is a beloved food that has been consumed by humans for centuries, and its production involves a fascinating interplay of microbes. The magic of cheese-making requires just four ingredients: milk, salt, rennet (or another coagulant), and microbes. However, the variety of microbes used in this process gives rise to the diverse range of cheeses we know and love today. These microbes, including bacteria, yeast, and filamentous fungi (molds), play a crucial role in fermentation, flavour development, and ripening, resulting in the distinctive characteristics of each cheese variety.
| Characteristics | Values |
|---|---|
| Number of microbes in a piece of cheese | 10 billion |
| Number of microbial species in a single cheese type | Over 100 |
| Microbes in cheese | Bacteria, yeast, filamentous fungi (molds) |
| Microbes added by cheesemakers | Bacteria, yeast, molds |
| Microbes introduced without cheesemaker's decision-making | Bacteria, native to the milk |
| Microbes introduced with decision-making from cheesemakers | Lactococci, Lactobacilli, Streptococci |
| Microbes that cause stinkiness | Brevibacterium linens |
| Microbes that cause holes in Swiss cheese | Propionobacter shermanii |
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What You'll Learn
Microbes are essential to the fermentation process
The magic of cheese happens with just four ingredients: milk, salt, rennet (or some other coagulant), and microbes. But it's the variety of microbes that bring us the variety of cheeses we enjoy. The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (molds). These microbes can be introduced into the cheese-making process in several ways. They can be added deliberately by the cheesemaker as a starter culture or they can enter the process unintentionally, through people, animals, insects, rodents, production equipment, or the environment.
Microbial fermentation is an enzyme-dependent process during which protein catalysts made by the microbes break down complex substances—in this case, the proteins and sugars within milk—into simpler products. This process preserves milk as cheese, allowing it to be consumed months or years later, long after the unfermented milk would have spoiled. The first microbial settlers in milk are typically lactic acid bacteria (LABs), which feed on lactose, the sugar in the milk, and produce acid. The increasing acidity causes the milk to sour, making it inhospitable to many spoilage organisms.
As cheese matures, the lactic acid bacteria and other early colonists give way to other species of bacteria and, eventually, fungi, in a process known as ecological succession. The specific species that are present depend on how the cheese is made and ripened, and the variety of cheese being produced. For example, the bacteria Propionobacter shermanii is able to digest acetic acid and convert it to sharp, sweaty-smelling propionic acid and carbon dioxide. This process gives Emmental and other Swiss cheeses their characteristic "holes" and complex, sharp bouquet.
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Microbes are introduced to cheese in several ways
Microbes are an essential part of the cheese-making process. They are introduced to cheese in several ways, some deliberate and some unintentional.
Cheese is made with only four ingredients: milk, salt, rennet (or another coagulant), and microbes. The microbes used in cheese are microscopic living organisms, including bacteria, yeasts, and moulds. The variety of microbes used in the process is what leads to the variety of cheeses we consume.
Another way microbes are introduced to cheese is through the natural environment. Environmental microbes from the cheese-making facility and aging facilities can settle on the cheese during production and as it ages. In some cases, aging facilities develop their own unique microbial communities that contribute to the character of the cheese they produce. Furthermore, microorganisms can inadvertently enter the cheese-making process from sources such as soil, bedding materials, feed, and even the teats of milking animals.
In addition to the natural introduction of microbes, cheesemakers may also intentionally add specific microbes to the cheese. This is often done to encourage flavour development and contribute to the complexity of the cheese. For example, the addition of adjuncts, such as Lactobacillus helveticus, can give cheeses like aged Gouda a pleasant sweet flavour.
Finally, microbes can be introduced to cheese through the traditional practice of inoculating new batches of cheese using whey or other products from previous batches. This method, used in many traditional cheeses, can result in the presence of dozens of different microbes, some highly unusual, contributing to the unique character of these cheeses.
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Microbes give cheese its distinctive flavour
Microbes are essential to the cheesemaking process and play a crucial role in giving cheese its distinctive flavour. While milk, salt, rennet (or another coagulant) are the other key ingredients, it is the microbes that bring variety to the cheeses we enjoy.
Cheese is one of the few foods that contain extraordinarily high numbers of living, metabolising microbes. Each piece of cheese may contain up to 10 billion microbes, more than there are people on Earth! These microbes are mostly safe to eat and are neither particularly harmful nor beneficial to our health. However, cheese can become contaminated with harmful microorganisms if it is improperly made or stored.
The broad groups of cheese-making microbes include bacteria, yeast, and filamentous fungi (molds). These microbes can be introduced into the cheese in various ways. Some are added intentionally by the cheesemaker, while others find their way into the cheese without any direct decision-making from the cheesemaker. For example, microbes native to the milk will be carried over to the cheese, and ambient organisms can also be introduced during the cheese-making and ageing processes. Some ageing facilities even develop their own desirable microbial communities symbiotically with the cheese they produce.
The first microbial settlers in milk are typically lactic acid bacteria (LABs), which feed on lactose, the sugar in the milk, and produce lactic acid. This process lowers the pH of the cheese, making it inhospitable to spoilage organisms. As the cheese matures, the LABs give way to other species of bacteria and eventually fungi, in a process known as ecological succession. The specific species that take over depend on how the cheese is made, ripened, and the variety of cheese.
Different microbes contribute to the distinctive flavours of various cheeses. For example, Propionobacter shermanii is found in alpine and Italian hard cheeses, and it is responsible for the sharp, sweaty-smelling propionic acid that gives these cheeses their complex, sharp bouquet. On the other hand, Brevibacterium linens is known for contributing to the stinkiness of certain cheeses, producing oniony, garlicky, fishy, and sweaty aromas.
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Microbes are responsible for the holes in some cheeses
Microbes are responsible for the distinctive holes in some cheeses, such as Swiss cheese (Emmental) and Gouda. The holes are created by bacteria, specifically Propionibacterium freudenreichii ssp. shermanii, which is added to the milk at the start of the cheese-making process. This bacterium converts lactic acid into carbon dioxide, propionic acid, and acetic acid. The carbon dioxide seeps into the cheese body and forms the holes, while the other acids contribute to the sharp and complex flavours associated with these cheeses.
The formation of holes in cheese is a result of the microbial activity of Propionibacterium freudenreichii, which grows during the ripening process at 24°C. This bacterium ferments lactate, producing acetate, propionate, and carbon dioxide (CO2). The carbon dioxide gas collects at weak spots in the cheese matrix, building up pressure until holes, or "eyes," form. If the P. freudenreichii fails to grow and the holes do not appear, the cheese is called "blind."
The microbial activity of other bacteria, such as Leuconostoc mesenteroides and Lactococcus lactis ssp. lactis biovar. diacetylactis, can also contribute to hole formation in Gouda cheese. In this case, citric acid is converted into carbon dioxide and diacetyl, which gives the cheese its buttery flavour.
Cheese is a traditional food that has been incorporated into many cuisines and is often consumed with wine or other beverages. It is one of the few foods that contain extraordinarily high numbers of living, metabolising microbes, with each piece of cheese containing up to 10 billion microbes. The broad groups of cheese-making microbes include bacteria, yeast, and filamentous fungi (molds). These microbes are introduced into the cheese-making process in various ways, such as through raw milk, added by the cheesemaker as "starter cultures," or present in the cheese ageing rooms.
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Modern cheesemaking has reduced microbial diversity
The process of cheesemaking involves the use of microbes, which are microorganisms like bacteria, yeast, and filamentous fungi (molds). These microbes are essential for fermentation, which preserves milk as cheese, allowing it to be consumed months or even years later. The specific microbes involved in cheesemaking can be introduced deliberately as starter cultures or unintentionally through various environmental factors.
Modern cheesemaking practices, however, have shifted towards controlled-inoculation methods, which have reduced microbial diversity in cheese. This shift has resulted in cheeses that may be less complex and interesting in terms of flavor and overall character. Traditional cheeses, with their diverse microbial communities, often exhibit a greater depth of flavor and uniqueness compared to their modern counterparts.
The reduction in microbial diversity in modern cheesemaking is attributed to the controlled nature of the process. In traditional cheesemaking, the cheese microbiota evolves through a succession of different microbial groups, resulting in a dynamic and complex community structure. This evolution is influenced by various factors, such as the environment, milk source, and aging processes. Traditional cheeses are often ripened in caves or cellars, providing cool and humid conditions that foster the growth of diverse microbes.
In contrast, modern cheesemaking plants utilize specialized ripening rooms with tightly controlled temperature and humidity levels. While this control ensures greater consistency in product quality, it also limits the variety of microbes that can thrive. The understanding of microbial interactions and their impact on cheese flavor and safety is still evolving, and modern microbiology has yet to fully explain the role of all microbes in these processes.
Additionally, the use of raw milk, which can introduce a wide range of microbes, has been largely replaced by pasteurized milk in modern cheesemaking. This further contributes to the reduction in microbial diversity. While controlled-inoculation methods ensure safety and consistency, they may not always allow for the development of the complex flavors and characteristics found in traditional cheeses with higher microbial diversity.
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Frequently asked questions
A single gram of fully ripened cheese rind may contain up to 10 billion bacteria, yeasts, and other fungi. Each piece of cheese may contain as many as 10 billion microbes.
The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (molds).
Microbes can be introduced into cheese either deliberately or unintentionally. They can be added as a starter culture or enter the cheese-making process from the soil, bedding materials, feed, etc.
Microbes are essential for the fermentation process in cheese-making. They break down complex substances in milk, such as proteins and sugars, and convert them into simpler products, preserving the milk as cheese. They also contribute to the distinctive flavor, smell, and texture of the cheese.
