Patrick Oconnell
Cheese is a versatile food that is incorporated into many cuisines and can be consumed directly or used as an ingredient in cooking. The process of making cheese involves microbial fermentation, where microbes break down the proteins and sugars in milk. This fermentation is essential for preserving milk as cheese, allowing it to be consumed months or even years later. The magic of cheese happens with just four main ingredients: milk, salt, rennet (or another coagulant), and microbes. However, the variety of microbes used in cheesemaking, including bacteria, yeast, and filamentous fungi (molds), gives rise to the diverse range of cheeses we know and love.
Characteristics and Values
| Characteristics | Values |
|---|---|
| Basic Ingredients | Milk, salt, rennet (or some other coagulant), and microbes |
| Bacteria | Lactic acid bacteria, streptococci, propionibacteria, smear bacteria, etc. |
| Fungi | White molds (P. camembertii or P. candidum), blue mold, Geotrichum, etc. |
| Microbial Sources | Marine microbes, sea salt, brine, human skin, etc. |
| Function of Bacteria | Convert milk sugar (lactose) to lactic acid, contribute to flavor, inhibit spoilage organisms, etc. |
| Function of Fungi | Produce enzymes that break down milk proteins, contribute to flavor and texture, etc. |
| Environmental Factors | Temperature, humidity, shape and texture of cheese, etc. |
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What You'll Learn
- Lactic acid bacteria are often called starter cultures
- Bacteria and fungi in cheese can be deadly or peaceful
- The variety of microbes in cheese give us the variety we enjoy
- Milk is pasteurized to kill bacteria and replaced with starter cultures
- The rind microbiota of cheeses with natural, smear, and bloomy rinds are composed of tractable microbial communities
Lactic acid bacteria are often called starter cultures
Lactic acid bacteria (LAB) are a diverse group of safe microorganisms that are used as starter cultures and probiotics. They are used in the production of many foods and beverages, including yogurt, cheese, kefir, kimchi, miso, and some charcuterie. LAB are the most important group of industrial microorganisms, with a market value of several billion dollars.
Lactic acid bacteria are called starter cultures because they initiate the fermentation process by producing lactic acid. They do this by consuming sugars (such as lactose) in the food matrix, which lowers the pH and inhibits spoilage organisms. This process also produces other beneficial compounds, such as organic acids, polyols, exopolysaccharides, and antimicrobial compounds, which improve the texture, aroma, flavour, health effects, and shelf life of the final product.
There are two main families of lactic acid bacteria: lactococci (sphere-shaped) and lactobacilli (rod-shaped). Streptococci are also important, especially in yoghurt-making. These bacteria are naturally found in the environment, and while some die off during the initial stages of cheesemaking, others survive and contribute to the cheese's flavour.
Cheesemakers often add starter cultures of beneficial bacteria to freshly formed curds. However, when the final product is analysed, it is found that many of the bacteria present were not in the original starter culture. These "microbial strangers" may come from the milk itself, or from other sources such as the sea salt used to wash the cheese.
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Bacteria and fungi in cheese can be deadly or peaceful
Cheese is a food that contains extraordinarily high numbers of living, metabolizing microbes. The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (molds). The magic that is cheese only really needs four ingredients: milk, salt, rennet (or some other coagulant), and microbes.
Cheese is made by first pasteurizing milk, which involves briefly heating it to high temperatures to kill the bacteria that come naturally with it. Then, they are replaced with standardized starter cultures. This has made cheesemaking more controlled but has also reduced the diversity of microbes in cheese.
During the ripening process, a second wave of diverse bacteria and fungi (secondary microbiota) grow within the cheese and on its surface, sometimes forming a rind. These microorganisms contribute enzymatic activities that affect the color, flavor, texture, and other important characteristics of the ripening cheese.
Some cheeses, like Saint-Nectaire, develop all kinds of crazy surface molds, most of which are not harmful and, in fact, contribute to the cheese's unique flavor. White molds, which are found on the outside of all types of soft-ripened cheeses, are subspecies of P. camembertii (also called P. candidum). These molds produce enzymes that break down milk proteins, leading to the characteristic ripened layer surrounding a firm interior.
Cheese rinds are complex microbial worlds that contain bacterial swimmers that hop on highways of fungal tendrils to get around. For example, the branched hyphae of a fungal mold like Mucor lanceolatus can coexist with the blobs of bacterial colonies like Serratia proteamaculans, which gives cheese a nice note of cooked cabbage.
While most bacteria and fungi in cheese are peaceful and contribute to its unique flavor, there can be deadly skirmishes between organisms, as noted by scientists. For instance, smear bacteria are responsible for the room-clearing ability of some cheeses, and Brevibacterium linens is a bacterium that contributes to the stinkiness of Limburger cheese.
In conclusion, the bacteria and fungi in cheese can be both deadly and peaceful, with most microbes contributing to the flavor, texture, and other characteristics of the cheese through complex interactions.
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The variety of microbes in cheese give us the variety we enjoy
The variety of microbes in cheese gives us the variety we enjoy. Indeed, it only takes four ingredients to make cheese: milk, salt, rennet (or some other coagulant), and microbes. However, there is a wide range of microbes that bring us the variety of cheeses we savour.
Lactic acid bacteria (LAB) are of great economic importance because they play a crucial role in the fermentation process of traditional cheeses. Their metabolic features contribute to the development of desirable sensory characteristics of food products. The microbiota of raw milk cheeses are quite complex and include numerous strains of non-starter lactic acid bacteria (NSLAB), which are very important for cheese ripening and flavour development.
Lactic acid bacteria are often called "starter cultures" as they play the main role in converting the basic milk sugar, lactose, into lactic acid. This step lowers the cheese pH and makes the cheese inhospitable to spoilage organisms. There are two main families of lactic acid bacteria: lactococci (sphere-shaped, lactic-acid-producing bacteria) and lactobacilli (rod-shaped, lactic-acid-producing bacteria). Streptococci can also play an important role in initial cheese ripening and are very important in yoghurt-making. Although many of these bacteria die off after the initial step of cheesemaking, some survive and continue to contribute to the cheese's flavour.
The details of which species are present depend on exactly how the cheese is made and ripened, and what variety it is. In some long-ripened cheeses such as Roquefort, researchers have detected hundreds of different kinds of bacteria and fungi. In some cheeses, more than 400 different kinds have been found. A single gram of rind from a fully ripened cheese might contain around 10 billion bacteria, yeasts and other fungi. As a 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 variety of microbes in cheese is also affected by the environment, such as temperature and humidity, and the shape and texture of the cheese. Different microbes prefer different surfaces to grow on. For example, blue mould likes crags and crevices, while Geotrichum likes flat surfaces.
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Milk is pasteurized to kill bacteria and replaced with starter cultures
Milk is often pasteurized to kill harmful bacteria and prevent foodborne illnesses. Pasteurization is a process where milk is heated to a specific temperature for a set period to destroy or deactivate microorganisms and enzymes that cause food spoilage or disease. The minimum pasteurization temperature is 63°C (145°F) for 30 minutes or 72°C (162°F) for 15 seconds. This process effectively kills pathogens like Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli O157:H7, among others.
While pasteurization improves food safety and extends shelf life, it also reduces the diversity of microbes in milk, which can impact the flavor of cheese made from pasteurized milk. Cheesemakers often add starter cultures of beneficial bacteria, known as lactic acid bacteria, to freshly formed curds. These bacteria play a crucial role in converting milk sugar (lactose) into lactic acid, lowering the cheese's pH, and inhibiting spoilage organisms.
The two main families of lactic acid bacteria are lactococci (spherical) and lactobacilli (rod-shaped). Streptococci are also important in initial cheese ripening and yogurt-making. These starter cultures contribute to the unique flavor profiles of various cheeses, especially alpine and Italian hard cheeses.
However, the microbial composition of ripened cheeses may differ significantly from the starter cultures due to the introduction of "microbial strangers" during the cheese-making process. These microbes can come from the sea salt used in brine or other sources, resulting in a diverse microbial ecosystem within the cheese.
In summary, milk is pasteurized to kill harmful bacteria and is then supplemented with starter cultures of beneficial bacteria to initiate the cheesemaking process and develop flavor. This combination of pasteurization and controlled microbial addition ensures safer, more consistent cheese production while maintaining some level of microbial diversity and flavor complexity.
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The rind microbiota of cheeses with natural, smear, and bloomy rinds are composed of tractable microbial communities
Cheese is made from milk, salt, rennet (or some other coagulant), and microbes. The microbial communities of cheese contribute to its safety, quality, and physicochemical and sensory properties. The rind microbiota of cheeses with natural, smear, and bloomy rinds are composed of tractable microbial communities.
Natural rind cheeses, such as clothbound cheddars, St. Nectaire, and Tomme de Savoie, are largely untouched during aging. The rind of a natural rind cheese is typically dry, with a higher salt concentration. The yeast Debaryomyces, the bacterium Staphylococcus, and the mold Penicillium are all highly abundant in natural rind communities.
Bloomy rind cheeses, such as Brie and Camembert, are heavily inoculated with fungi to create a dense, usually white rind. The fungus Galactomyces and four genera of Proteobacteria are found in high abundance on moist bloomy rinds.
Washed rind cheeses, such as Taleggio, Gruyere, and Epoisses, are initially produced similarly to bloomy or natural rind cheeses but are then washed repeatedly with a salt solution during aging. The composition of these cheeses is interspersed throughout the bloomy and natural rind communities.
The microbial communities of cheese can vary greatly depending on the production process and the environment. For example, the presence of marine microbes in cheese has been linked to the use of sea salt in cheese production or the brine used to wash cheeses. Additionally, the microbial diversity of the rind region is higher than that of the core region, as processes such as smoking and soaking directly affect the rind.
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Frequently asked questions
Cheese is made from milk, salt, rennet (or some other coagulant), and microbes.
Microbes are used in cheese-making to break down milk proteins and sugars, preserving milk as cheese. Lactic acid bacteria, for example, convert milk sugar (lactose) into lactic acid, lowering the pH of the cheese and making it inhospitable to spoilage organisms.
The microbes used in cheese-making include bacteria, yeast, and filamentous fungi (molds). Examples of bacteria used in cheese-making include lactic acid bacteria, Brevibacterium linens, and Propionibacterium freudenreichii.
