Andy Montoya
Cheese is made using a combination of bacteria, yeast, and moulds. These microbes break down milk fats and proteins, giving cheese its creamy texture and flavour. The specific microbes used in cheesemaking depend on the type of cheese being produced. For example, blue cheese is made using Penicillium roqueforti and Penicillium glaucum, which give the cheese its distinctive flavour and texture. Other types of cheese, such as Camembert and Brie, are inoculated with mould on the surface, while some cheeses are curdled using acidity or rennet, a mixture containing the active enzyme chymosin. Modern cheesemaking often involves controlled inoculation with preselected cultures, while traditional cheesemaking may use dozens of microbe types, including those from previous batches of cheese.
| Characteristics | Values |
|---|---|
| Broad groups | Bacteria, yeast, and filamentous fungi (molds) |
| Types of bacteria | Lactic acid bacteria (LAB), lactococci, lactobacilli, streptococci, mesophilic bacteria, thermophilic bacteria |
| Bacteria examples | Lactobacillus casei ssp. casei, Propionibacterium freudenreichii ssp. shermanii, Brevibacterium linens |
| Yeast examples | Geotrichum candidum |
| Fungi examples | Penicillium, Roqueforti, P. glaucum |
| Other microorganisms | Corynebacteria |
| Microbe sources | Intentionally added to milk, drifted from the environment or cheesemakers |
| Microbe functions | Convert milk sugar lactose into lactic acid, break down milk fats and proteins, determine flavor and texture |
| Microbe-related processes | Fermentation, inoculation, coagulation, backslopping |
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What You'll Learn
- Bacteria, yeast, and moulds are all microbes used in cheesemaking
- Lactic acid bacteria are often used as starter cultures
- Brevibacterium linens are responsible for the strong smell of some cheeses
- Blue moulds grow in low-oxygen environments, making them perfect for blue cheese
- Microbes are added to milk at different temperatures to create different types of cheese
Bacteria, yeast, and moulds are all microbes used in cheesemaking
Bacteria play a crucial role in cheesemaking. Lactic acid bacteria (LAB) are a group of bacteria that convert the milk sugar lactose into lactic acid, lowering the pH of the milk and inhibiting the growth of spoilage organisms. This process is essential for transforming milk into cheese. There are two main types of lactic acid bacteria: lactococci, which are spherical in shape, and lactobacilli, which are rod-shaped. Traditional cheesemakers relied on naturally occurring LAB in milk, but modern cheesemakers often use industrial starter cultures, which are specifically chosen for their ability to produce consistent levels of acid.
Yeast is another important microbe in cheesemaking. Geotrichum candidum, for example, is a yeast that exhibits mould-like characteristics and is responsible for the "brainy" appearance of some cheeses. Yeast is commonly used in moulded and surface-ripened cheeses, contributing to their distinctive characteristics.
Moulds are also used in cheesemaking. Blue moulds, such as Penicillium roqueforti and P. glaucum, are famous for their role in creating the unique flavour and texture of blue cheeses like Roquefort, Stilton, and Gorgonzola. These moulds thrive in low-oxygen environments, making them ideal for the small cracks in ripening cheese. Cheesemakers pierce and inoculate channels in the cheese to encourage the growth of these moulds. White moulds, a subspecies of P. camembertii, are found on the outside of soft-ripened cheeses like Camembert and Brie.
The interaction between these microbes and their environment during cheesemaking results in the diverse flavours, textures, and characteristics of cheese. Each type of microbe contributes uniquely to the final product, highlighting the importance of microbial selection and cultivation in the art of cheesemaking.
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Lactic acid bacteria are often used as starter cultures
There are two main families of lactic acid bacteria: lactococci and lactobacilli. Lactococci are spherical in shape and actively produce lactic acid. On the other hand, lactobacilli have a rod-like structure and are responsible for producing lactic acid as well. Streptococci, another type of bacteria, also contribute to the initial ripening of cheese and are commonly used in yoghurt-making.
The use of lactic acid bacteria as starter cultures can be traced back to traditional cheesemaking practices. In the past, cheesemakers relied on naturally occurring lactic acid bacteria (LAB) present in milk. However, modern cheesemaking often involves inoculating milk with industrial starter cultures, which are specifically selected bacteria that ensure consistent and reliable acid production. This practice enhances control over the cheesemaking process and contributes to the desired flavour and texture profiles.
The process of using starter cultures begins with warming the milk to the optimal growth temperature for the microbes in the culture. This temperature adjustment accelerates fermentation and promotes the formation of curds, which are essential for the transformation of milk into cheese. The acid produced during fermentation also contributes to syneresis, which is the removal of water from milk proteins.
While lactic acid bacteria are commonly used as starter cultures, it's important to note that other microbes, such as bacteria, yeast, and filamentous fungi (molds), also play a significant role in cheese-making. The interplay between these microorganisms creates the unique characteristics of different cheese varieties.
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Brevibacterium linens are responsible for the strong smell of some cheeses
Cheese is a food that contains a high number of living, metabolizing microbes. The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (molds). Each type of cheese has a unique microbial composition, and the combination of microorganisms is what creates the distinctive characteristics of each cheese.
Brevibacterium linens (B. linens) is a gram-positive, rod-shaped bacterium that is commonly found on human skin and is responsible for foot odour. This bacterium is also used in the production of certain cheeses, specifically washed-rind and smear-ripened cheeses. B. linens is added to the cheese's surface, where it contributes to the desired flavour and aroma profiles of these cheeses. It is also known to produce antimicrobial substances, specifically bacteriocins, which inhibit the growth of foodborne pathogens such as Staphylococcus aureus and Listeria monocytogenes.
B. linens is particularly good at breaking down proteins into stinky odor compounds, producing oniony, garlicky, fishy, and sweaty aromas. These odor compounds are due to sulfur-containing compounds called S-methyl thioesters, as well as methanethiol, a very volatile compound with a low odor threshold and a characteristic “cabbage-like” or “rotten egg-like” odor. The production of these volatile sulfur compounds is highly strain-dependent, and the orange colour of B. linens is considered to be responsible for the orange hue of the cheese.
B. linens is used in the fermentation of several washed-rind and smear-ripened cheeses, such as Munster, Limburger, Tilsit, Port-Salut, Raclette, Livarot, Pont l'Eveque, Époisses, Wisconsin Brick, Năsal, and Pálpusztai. It is also used in the production of blue cheese, in addition to the mold Penicillium roqueforti. The inclusion of B. linens in an aseptic cheddar cheese slurry system resulted in an enhanced production of methanethiol, contributing to the distinctive flavor of good-quality Cheddar.
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Blue moulds grow in low-oxygen environments, making them perfect for blue cheese
Blue cheese is believed to have been discovered by accident when cheeses were stored in caves with controlled temperature and moisture levels, which happened to be favourable environments for varieties of harmless mould. The specific strain of mould, Penicillium roqueforti, was found to be growing in a cave outside the village of Roquefort in France. This mould is now refined and used for almost all blue cheeses.
Blue moulds, such as Penicillium roqueforti and Penicillium glaucum, are added at the beginning of the cheese-making process but remain dormant until the conditions are right for them to grow. Once the cheese curd has been 'moulded', the moulds need oxygen to grow, which is provided by piercing the cheese with thin needles or skewers. The blue mould then matures inside the air tunnels, developing flavour and texture as it ages.
Blue moulds are capable of growing in remarkably low-oxygen environments, which makes them perfectly suited for the small cracks in the interior of a ripening cheese. Cheesemakers regularly pierce and inoculate channels through the cheese to encourage the growth of these moulds. The blue veins that develop enhance the flavour of the cheese, as the mould breaks down fat and protein in the cheese.
The distinctive flavour and aroma of blue cheese arise from methyl ketones, which are a metabolic product of Penicillium roqueforti. While some mycotoxins are present at low levels, the combination of acidity, salinity, moisture, density, temperature, and oxygen flow creates an environment that is unsuitable for the production of toxins. This makes blue moulds safe for cheese-making, despite their ability to grow in low-oxygen environments.
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Microbes are added to milk at different temperatures to create different types of cheese
Cheese is created through the decomposition of milk fats and proteins by microbes. The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (molds). The specific microbes used and the temperature at which they are added to the milk determine the type of cheese that will be produced.
Lactic acid bacteria (LAB) are commonly used in cheese-making to convert lactose, the milk sugar, into lactic acid. This process lowers the pH of the milk, making it inhospitable to spoilage organisms. There are two main families of lactic acid bacteria: lactococci, which are sphere-shaped, and lactobacilli, which are rod-shaped. Mesophilic bacteria, which thrive at room temperature but die at higher temperatures, are used to make mellow cheeses such as Cheddar, Gouda, and Colby. On the other hand, thermophilic bacteria, which thrive at higher temperatures of around 55°C, are used to make sharper cheeses such as Gruyère, Parmesan, and Romano.
The temperature at which the microbes are added to the milk also plays a crucial role in the cheese-making process. For example, in the production of Swiss cheese and Gouda, the action of certain bacteria, such as Propionibacterium freudenreichii ssp. shermanii, results in the formation of eyes or holes in the cheese. The carbon dioxide produced by these bacteria seeps into the cheese body, creating the distinctive appearance of these cheeses.
Additionally, some cheeses are inoculated with specific fungi during the ripening process. For example, Camembert and Brie are surface-ripened with Penicillium, while blue vein cheeses are internally inoculated with Penicillium roqueforti and Penicillium glaucum, giving them their unique flavor and texture.
The length of time that cheese is aged also impacts the final product. Young, fresh cheeses are not aged, while hard cheeses are typically aged for a minimum of 6 months to one year. The longer a cheese is aged, the sharper its flavor becomes. For example, mild Cheddar is aged for 2-3 months, while extra sharp Cheddar can be aged for up to 5 years.
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Frequently asked questions
The microbes used to make cheese include bacteria, yeast, and filamentous fungi (molds). Examples of bacteria include lactic acid bacteria (LAB), which are often called "starter cultures", and Brevibacterium linens, which is responsible for the distinctive aroma of many surface-ripened cheeses. Examples of moulds include blue moulds such as Roqueforti and P. glaucum, which give rise to the unique flavour and texture of blue cheese, and white moulds, which are subspecies of P. camembertii.
Microbes turn milk into cheese by breaking down milk fats and proteins, which makes cheese creamy and gives it flavour. The milk sugar lactose is broken down into lactic acid by a group of bacteria called lactic acid bacteria (LAB). This process lowers the pH of the milk and makes it inhospitable to spoilage organisms.
Cheesemakers control which microbes grow on the cheese by manipulating the temperature, salt, acidity, and other variables of the environment in which the cheese matures. For example, to encourage the growth of blue moulds, cheesemakers pierce and inoculate channels through the cheese to provide an environment with low oxygen levels in which the mould can grow.
Traditional cheeses are inoculated using whey or other products from previous batches, which means they can contain dozens of types of microbes, some of which may be highly unusual. Modern cheeses, on the other hand, are usually made with preselected cultures consisting of only a few types of microbe, making them less complex than traditional cheeses.
