Patrick Oconnell
Cheese is a beloved food item found in almost all cultures and is probably one of the oldest processed foods. The process of making cheese involves milk coagulation, which can be enzymatic or acidic, resulting in a semi-solid curd. The magic of cheese-making involves four key ingredients: milk, salt, rennet (or another coagulant), and microbes. While not all cheeses are made with bacteria, bacteria plays a crucial role in the cheesemaking process and the final product's flavour and texture. The specific bacteria and fungi in cheese depend on the cheesemaking method and variety.
| Characteristics | Values |
|---|---|
| Number of ingredients required to make cheese | Four |
| Ingredients | Milk, salt, rennet (or some other coagulant), and microbes |
| Microbes | Bacteria, yeast, molds, etc. |
| Types of bacteria | Lactic acid bacteria, Propionibacterium freudenreichii ssp. shermanii, Streptococcus thermophilus, Lactococcus lactis ssp lactis biovar. diacetylactis, Leuconostoc mesenteroides, Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. cremoris |
| Types of molds | Blue mold, white mold, Penicillium, P. camembertii (also called P. candidum) |
| Microbial wealth | Traditional cheeses are more complex than modern, controlled-inoculation cheeses |
| Pasteurization | Milk is often pasteurized to kill bacteria that come naturally with it |
| Role of bacteria | Converts lactose to lactic acid, acidifying the milk, inhibiting the growth of undesirable microorganisms, converting lactic acid into carbon dioxide, propionic acid, and acetic acid, producing holes in Swiss cheese, contributing to flavor |
| Number of bacteria | A single gram of rind from a fully ripened cheese might contain around 10 billion bacteria |
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What You'll Learn
The role of microbes in cheese-making
Cheese is one of the oldest processed foods, and its production involves the coagulation of milk, which can be enzymatic or acidic. The magic of cheese happens with just four ingredients: milk, salt, rennet (or another coagulant), and microbes.
The role of microbes in cheesemaking is of utmost importance. The process involves a complex interplay of bacteria, yeasts, and moulds, which contribute to the unique characteristics of different cheeses. The microbial diversity in cheese has been influenced by modern practices such as machine milking and the use of sealed storage tanks, which have reduced the variety of microbes in the milk. However, cheesemakers still intentionally add specific microbes to the milk early in the process to induce fermentation and develop flavour.
Lactic acid bacteria, often called "starter cultures", play a pivotal role in converting milk sugar (lactose) into lactic acid. This step lowers the cheese's pH, making it unwelcoming to spoilage organisms. There are two main families of lactic acid bacteria: lactococci (sphere-shaped) and lactobacilli (rod-shaped). Streptococci are also important in the initial ripening of cheese. These bacteria can be added intentionally or may be present in the raw milk, and they contribute to the cheese's flavour and nutritional value.
The specific bacteria and fungi present in cheese depend on the cheesemaking process, ripening methods, and variety. Different bacteria thrive under different conditions; for example, heating milk to over 120 degrees Fahrenheit suits heat-loving bacteria like Streptococcus thermophilus, ideal for mozzarella. Manipulating factors such as temperature, curd size, and salt content allows cheesemakers to curate the desired microbes for their product.
The maturation process of cheese involves an ecological succession of microbes. As the cheese matures, the early lactic acid bacteria give way to other bacteria and eventually fungi. The rind of a fully ripened cheese can host up to 10 billion bacteria, yeasts, and fungi per gram. The specific microbes present contribute to the unique characteristics of different cheeses, such as the holes in Swiss cheese formed by the action of Propionibacterium freudenreichii ssp. shermanii, or the blue moulds in Roquefort, Stilton, and Gorgonzola.
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The different types of bacteria used
The process of making cheese involves the use of various bacteria, which play a crucial role in developing its flavour, texture, and overall character. Here is an overview of the different types of bacteria commonly employed in cheesemaking:
Lactic Acid Bacteria (LAB)
Lactic acid bacteria, often referred to as "starter cultures," are essential in traditional cheesemaking. They rapidly convert milk sugar (lactose) into lactic acid, reducing the pH of the cheese and inhibiting the growth of unwanted bacteria. This process is known as acidification and is fundamental to cheese production. There are two main families within the LAB group: lactococci, which are spherical in shape, and lactobacilli, which have a rod-like structure. Streptococci, another type of bacteria, also play a role in the initial ripening of cheese and are commonly used in yoghurt-making.
Thermophilic Bacteria
Thermophilic species such as Streptococcus thermophilus, Lactobacillus helveticus, and Lactobacillus delbrueckii are commonly associated with Swiss and Italian-type cheeses. As the name suggests, these bacteria thrive in high-temperature environments, and their heat tolerance makes them ideal for creating cheeses like mozzarella.
Mesophilic Bacteria
In contrast to thermophilic bacteria, mesophilic bacteria operate at lower temperatures, fermenting lactose at 105°F or less. Examples of mesophilic species include Lactococcus lactis and Leuconostoc mesenteroides, which are instrumental in the production of cheeses such as Cheddar and Gouda.
Propionibacter shermanii
This bacterium is particularly noteworthy for its role in creating the distinctive characteristics of Swiss cheeses like Emmental. Propionibacter shermanii can convert acetic acid into propionic acid and carbon dioxide. The carbon dioxide forms the characteristic "holes" in Swiss cheeses, while the propionic acid contributes to their sharp, pungent aroma.
Molds and Their Bacteria
Molds, primarily of the Penicillium species, are also important in cheesemaking. White molds, a subspecies of P. camembertii (also known as P. candidum), are commonly found on soft-ripened cheeses. These molds produce enzymes that break down milk proteins, resulting in the ripened layer surrounding a firm interior. Additionally, blue molds like Penicillium Roqueforti frequently grow on the surface of goat cheeses, adding colour and flavour.
The art of cheesemaking involves carefully cultivating specific bacteria and environmental conditions to create desired flavours and textures. The variety of bacteria used in this process contributes to the diverse range of cheeses enjoyed worldwide.
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How bacteria affect flavour and ripening
The role of bacteria in cheese-making is complex and multifaceted. While the process of cheese-making has become more sanitised and controlled over time, bacteria remain essential to the development of flavour and texture in cheese.
Lactic acid bacteria, often called "starter cultures", play a pivotal role in converting milk sugar (lactose) into lactic acid. This process lowers the pH of the cheese, making it less hospitable to spoilage organisms. There are two main families of lactic acid bacteria: lactococci (sphere-shaped) and lactobacilli (rod-shaped). Streptococci are also important, especially in the initial stages of cheese ripening and yoghurt-making.
During the ripening process, a wide range of biochemical and microbiological changes occur. The specific bacteria present depend on the variety of cheese, the production method, and the ripening environment. For example, Propionibacterium freudenreichii is responsible for the distinctive eyes and flavour of Swiss-type cheeses, while Penicillium camemberti and P. roqueforti dominate the ripening of Camembert-type and Blue cheeses, respectively.
The temperature at which cheese is made and stored also influences the types of bacteria present. Heating milk to over 120 degrees Fahrenheit, for instance, kills off all bacteria except heat-loving strains like Streptococcus thermophilus, which is used in the making of mozzarella. The size of the curds, the amount of salt added, and the humidity level also impact the bacterial profile of the final product.
Bacteria interact with other microorganisms, such as moulds and yeasts, to create the unique flavour and texture profiles of different cheeses. These microbial interactions are complex and not yet fully understood by modern microbiology. However, it is clear that the presence and activity of various bacteria are essential in shaping the characteristics and quality of cheese.
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The impact of pasteurisation on cheese bacteria
Milk, salt, rennet (or another coagulant), and microbes are the four primary ingredients in cheese. The process of cheesemaking has evolved over time, becoming safer and cleaner. However, this has had an impact on the microbial diversity in cheese. Pasteurisation, or the heating of milk, is a common practice to ensure the safety of the milk supply by killing harmful bacteria. While this process makes cheesemaking more controlled and predictable, it also reduces the variety of microbes in the final product.
Prior to the widespread adoption of pasteurisation, cheesemakers relied on natural bacteria and other microorganisms present in raw milk to initiate fermentation, a process known as "ripening," which is crucial for developing the flavour and texture of cheese. With pasteurisation, beneficial bacteria and enzymes are also destroyed, making it challenging to create cheese with the same complex flavour and texture. This has led some cheesemakers to explore alternative methods, such as using starter cultures, to reintroduce beneficial bacteria to their cheese.
Different types of pasteurisation techniques exist, each with varying impacts on the milk's bacterial flora. Low-temperature long-time (LTLT) pasteurisation, favoured by small-scale and artisanal cheesemakers, heats milk to 63°C for 30 minutes, resulting in less damage to the milk's bacteria and potentially better cheesemaking outcomes. Thermalisation, a milder form of milk treatment, falls between raw and pasteurised milk, heating milk to a lower temperature for a longer period, killing some harmful bacteria but not all. High-Temperature Short-Time (HTST) pasteurisation, commonly used in large-scale cheese-making facilities, involves heating milk to 72°C for 15 seconds, offering more control and predictability in cheesemaking.
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The health benefits of cheese bacteria
Cheese is made using milk, salt, rennet (or some other coagulant), and microbes. The process of cheesemaking involves setting the right conditions for the "rot" of the milk. Different bacteria and fungi thrive under different conditions, and the cheesemaking process introduces variety and nuance. For example, heating milk to over 120 degrees Fahrenheit will kill off all bacteria except for heat-loving Streptococcus thermophilus, which is used to make mozzarella.
Cheese bacteria play a crucial role in converting milk sugar (lactose) into lactic acid, lowering the cheese's pH and inhibiting the growth of spoilage organisms. This process also produces flavour compounds that contribute to the unique taste of each cheese.
Some types of cheese, including Swiss and Gouda, are a good source of probiotics, which can help foster the growth of good bacteria in the gut. Eating foods with probiotics can help restore the natural balance of gut bacteria, which is believed to be linked to various health conditions such as allergies, mood disorders, and arthritis. Additionally, a study found that consuming cheese and milk might help modify gut bacteria to reduce the production of TMAO, a metabolite associated with cholesterol transport to the arteries and increased mortality rates.
However, it is important to consume cheese in moderation due to its high-calorie, saturated fat, and sodium content. Cottage cheese, a low-calorie option, is a healthy alternative for those who want to increase their dairy intake without the high fat and calorie content of other cheeses. It is also a good source of protein, vitamins, and minerals essential for bone health.
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Frequently asked questions
Yes, all cheese is made with bacteria. In addition to milk, salt, and rennet (or another coagulant), microbes are a necessary ingredient in the cheesemaking process.
There are thousands of microbes that can be used to make cheese, but some common bacteria include lactic acid bacteria, Streptococcus thermophilus, and Propionibacterium freudenreichii ssp. shermanii.
Bacteria are necessary for making cheese because they induce the fermentation process, converting lactose to lactic acid and acidifying the milk. This lowers the cheese's pH, making it inhospitable to spoilage organisms.
