Frederic Melton
Cheese is a dairy product made from milk, usually from cows, goats, or sheep. It is produced in a variety of flavours, textures, and forms through the coagulation of milk protein. The process of cheesemaking involves separating milk into solid curds and liquid whey by acidifying (souring) the milk and adding rennet. This acidification is achieved by adding bacteria, known as starter cultures or cheese cultures, which convert milk sugars into lactic acid. These bacteria play a crucial role in developing the flavour and texture of the cheese. Different types of cheese use various bacteria strains, including Lactococcus, Lactobacillus, Streptococcus, and Brevibacterium linens. The presence of bacteria, along with other microorganisms, contributes to the unique characteristics of each cheese variety.
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What You'll Learn
Bacteria and moulds in traditional cheesemaking
Bacteria and moulds are essential to traditional cheesemaking. The process of cheesemaking requires the ripening or culturing of milk. Cheese cultures are a group of specific bacteria strains that are combined to make a particular type of cheese. They are also used to help good bacteria in the milk flourish and lead to a more rich and developed flavour. All cultures accomplish the same basic task—their primary function is to raise the acidity of milk by absorbing lactose (a natural sugar found in milk) and transforming it into lactic acid. This part is especially beneficial in the cheesemaking process for three reasons. Firstly, the acid helps the milk split into particles called curds, an essential ingredient for producing cheese. Secondly, it contributes to the removal of water held within the milk proteins. Finally, it lowers the cheese's pH, making it inhospitable to spoilage organisms.
There are two main families of lactic acid bacteria (LAB): 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. The two most common types of cheese cultures are mesophilic, which work at moderate or medium temperatures of up to 90°F, and thermophilic, which work at warmer temperatures between 68-125°F. The temperature of the milk is adjusted to the optimal growth temperature of the microbes in the starter culture.
In traditional cheesemaking, bacteria and moulds might be already present in the aging room, and they are allowed to settle and grow on the stored cheeses. Nowadays, prepared cultures are more commonly used, giving more consistent results and putting fewer constraints on the environment where the cheese ages. These include soft ripened cheeses such as Brie and Camembert, blue cheeses such as Roquefort, Stilton, and Gorgonzola, and rind-washed cheeses such as Limburger.
The specific bacteria and moulds used in cheesemaking vary depending on the type of cheese being made. For example, Swiss cheese and, to a lesser extent, Gouda are known for their holes, which are formed by the action of certain bacteria. In Swiss cheese, Propionibacterium freudenreichii ssp. shermanii converts lactic acid into carbon dioxide, propionic acid, and acetic acid, with the carbon dioxide creating the holes. In Gouda, bacteria such as Leuconostoc mesenteroides and Lactococcus lactis ssp lactis biovar. diacetylactis convert citric acid into carbon dioxide and diacetyl, which gives the cheese its buttery flavour. The two main types of moulds found in cheese are blue and white. White mould, such as Penicillium camemberti, is responsible for the characteristic white rind on cheeses like Camembert and Brie, as well as the texture and some of the associated aromas.
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How bacteria affects cheese texture
Bacteria plays a crucial role in shaping the texture of cheese. The microbes introduced into cheese at every step of the cheese-making process, from the types of bacteria and mould used to the aging process, have a significant impact on the final product.
During the cheese-making process, bacteria are added to the milk to induce the fermentation process. This process involves the conversion of lactose to lactic acid, acidifying the milk. The acid produced during fermentation helps to form curds, contributing to the removal of water from the milk proteins. The ratio of salt to moisture influences the final pH, which can cause crystals to form on and within the cheese. Crunchy crystals can form in aged, hard cheeses such as Comté and Parmigiano-Reggiano, and are considered a desirable feature. On the other hand, gritty crystals are considered a defect in cheeses such as Cheddar.
As cheese ages, the bacteria and mould continue to grow and ferment, giving the cheese a stronger flavour and a different texture. For example, a young cheddar will have a milder flavour and a softer texture compared to an aged cheddar, which will have a sharper flavour and a firmer texture. Similarly, an aged blue cheese will have a stronger, more pungent flavour and a crumbly texture compared to a young blue cheese.
The environmental factors, such as the terroir, also play a role in shaping the cheese's texture. Terroir refers to the climate, soil, and local flora and fauna. For instance, the type of pasture that cows or goats graze on can influence the texture of the cheese. Additionally, the specific type of mould present in the environment can also affect the texture of the cheese.
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Bacteria and the cheese-making process
Bacteria play a crucial role in the cheese-making process, contributing to the flavour, texture, and overall character of the final product. The process typically involves the use of starter cultures, which are specially grown bacteria, specifically chosen for their ability to transform milk into cheese. These starter cultures can be classified as either mesophilic, which works at moderate temperatures, or thermophilic, which thrives in warmer environments.
The starter bacteria are responsible for converting milk sugars, specifically lactose, into lactic acid. This process of fermentation not only lowers the pH of the mixture, making it inhospitable to spoilage organisms, but also aids in the formation of curds. The milk is warmed to the optimal temperature for microbial growth, promoting the production of acid and the development of curds. The curds, solid in form, are then separated from the liquid whey and pressed into the desired cheese variety.
Different types of cheese call for specific combinations of bacteria strains and ratios. For instance, Swiss cheese and Gouda are known for their "eyes" or holes, which are formed by the action of bacteria such as Propionibacterium freudenreichii ssp. shermanii. This bacterium converts lactic acid into carbon dioxide, propionic acid, and acetic acid, with the carbon dioxide creating the distinctive holes. In contrast, Gouda's smaller holes are often the result of bacteria like Leuconostoc mesenteroides and Lactococcus lactis ssp lactis biovar. diacetylactis, which convert citric acid into carbon dioxide and diacetyl, lending a buttery flavour.
Artisanal cheese-making embraces the use of raw milk, traditional utensils, and hands-on methods, allowing for adjustments during production to accommodate variations in milk composition and fermentation rates. On the other hand, mass-produced cheese relies on pooled milk from multiple herds and automated processes, with standardised milk and starter activity, eliminating the need for adjustments.
The introduction of bacteria in cheesemaking has evolved over time. Traditional methods relied on bacteria naturally present in the environment or recycled from earlier batches, resulting in a more diverse microbial population. Modern practices, however, often employ controlled inoculation with preselected cultures, yielding more standardised cheese but potentially sacrificing the complexity of flavours and textures found in traditional varieties.
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Types of bacteria used in cheese
Cheese is a type of dairy product with a wide range of flavours, textures, and forms. It is produced by coagulating the milk protein casein, which comes from the milk of cows, goats, sheep, or water buffalo. During production, milk is usually acidified, and enzymes or bacterial enzymes are added to cause the casein to coagulate. The solid curds are then separated from the liquid whey and pressed into finished cheese.
The process of cheesemaking involves ripening or culturing the milk. Cheese cultures are a group of specific bacteria strains that are combined to make a particular type of cheese. They also help good bacteria in the milk flourish and lead to a more rich and developed flavour. All cultures have the same basic function: to raise the acidity of milk by absorbing lactose (a natural sugar found in milk) and transforming it into lactic acid. This helps the milk split into particles called curds, an essential ingredient in cheese production.
There are two main families of lactic acid bacteria (LAB): 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. The most common types of cheese culture are mesophilic, which work at moderate or medium temperatures of up to 90°F, and thermophilic, which work at warmer temperatures between 68-125°F.
Cheese cultures can be differentiated by the temperature at which they work, the type of bacteria strains they contain, and the ratio of each strain present. For example, the starter culture for Swiss cheese includes Propionibacterium freudenreichii, which produces propionic acid and carbon dioxide gas bubbles during aging, giving the cheese its distinctive holes or "eyes". On the other hand, Gouda cheese gets its eyes from bacteria such as Leuconostoc mesenteroides and Lactococcus lactis ssp lactis biovar. diacetylactis, which convert citric acid into carbon dioxide and diacetyl (buttery flavour).
Some cheeses have additional bacteria or moulds intentionally introduced before or during aging. Traditional cheesemaking relied on microbes that were already present in the aging room, while modern cheesemaking uses prepared cultures, giving more consistent results. These include soft ripened cheeses such as Brie and Camembert, blue cheeses such as Roquefort and Stilton, and rind-washed cheeses such as Limburger.
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How bacteria influences cheese flavour
Bacteria play a crucial role in the flavour formation of cheese, and this is influenced by various factors such as the type of bacteria, the milk used, and the cheesemaking process.
Firstly, let's delve into the types of bacteria commonly used in cheesemaking and their impact on flavour. The most prevalent bacteria employed in cheesemaking belong to the Lactococcus, Lactobacillus, and Streptococcus genera. These bacteria are referred to as lactic acid bacteria (LAB) due to their ability to convert milk sugars into lactic acid. This conversion not only curdles the milk but also significantly influences the flavour profile of the cheese. For instance, the bacterium Propionibacterium freudenreichii, commonly found in Swiss cheese starters, produces propionic acid and carbon dioxide, resulting in the distinctive "eyes" or holes in cheeses like Emmental. Additionally, specific bacteria, such as Brevibacterium linens, contribute to the strong aroma associated with surface-ripened cheeses.
The milk used in cheesemaking also plays a pivotal role in flavour development. Milk sourced from cows, goats, sheep, or water buffalo inherently contains various bacteria, which can influence the final flavour of the cheese. Traditional cheesemakers often relied solely on these naturally occurring bacteria to develop unique flavours in their cheeses. The animal's diet and the milk's pasteurization status further contribute to the flavour nuances in the final product.
The cheesemaking process itself offers another dimension to bacterial influence on flavour. During cheesemaking, milk is acidified, causing it to separate into solid curds and liquid whey. This acidification is often achieved through the use of starter bacteria or the addition of acids like vinegar. The type of bacteria and the specific enzymes they produce during this process greatly impact the flavour of the aged cheeses. Moreover, the addition of rennet, a coagulating agent, allows for curdling at lower acidity levels, as high acidity can inhibit the growth of flavour-making bacteria. The ratio of acid to rennet also determines the texture of the cheese, with softer, fresher cheeses having a higher proportion of acid.
Furthermore, the ripening or ageing process of cheese introduces a second wave of bacteria and fungi (secondary microbiota) that contribute to flavour development. This can occur naturally in the environment or through the use of prepared cultures, as seen in cheeses like Brie and Camembert. The specific conditions, such as salt concentration and nutrient content, during this ripening process also shape the microbial ecologies that develop, thereby influencing the final flavour profile.
In conclusion, bacteria play a pivotal role in shaping the flavour of cheese. From the bacteria naturally present in the milk to the carefully selected starter cultures and secondary microbiota, each step of the cheesemaking process offers an opportunity for bacteria to impart their unique characteristics on the final product. The complex biochemical reactions driven by these microorganisms result in the diverse flavours, textures, and aromas that we associate with different varieties of cheese.
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Frequently asked questions
Bacteria is used in the production of many cheeses, including Brie, Camembert, Blue Cheese, Mozzarella, Parmesan, Provolone, Swiss, Romano, Cheddar, Jack, Edam, Gouda, and many more.
The two main families of bacteria used in cheesemaking are lactococci (sphere-shaped, lactic-acid producing bacteria) and lactobacilli (rod-shaped, lactic-acid producing bacteria). Streptococci are also used in initial cheese ripening.
Bacteria are used to raise the acidity of milk by converting lactose into lactic acid, which helps the milk split into curds and contributes to the eventual flavour of the cheese.
