Andy Montoya
Cheese is a dairy product made from milk, salt, rennet (or another coagulant), and microbes. The variety of cheeses we enjoy today is made possible by the different microbes used in the cheesemaking process. These include bacteria, yeasts, and moulds, which can be introduced through the environment, or through prepared cultures. Microbes are responsible for the unique flavours and textures of cheese, as they break down proteins and produce various compounds during the ripening process. Some common microbes used in cheesemaking include Lactobacillus helveticus, which gives cheese a sweet flavour, and Brevibacterium linens, which is known for producing strong odours.
| Characteristics | Values |
|---|---|
| Microbes used in cheese | Bacteria, yeast, and filamentous fungi (molds) |
| Types of bacteria | Lactic acid bacteria (LAB), lactococci, lactobacilli, streptococci, mesophilic bacteria, thermophilic bacteria |
| Yeast examples | Geotrichum candidum, Brevibacterium linens |
| Mold examples | Blue veins, aromatic molds on the rind |
| Microbe sources | Naturally occurring in milk, added as starter cultures, from the environment, recycled from earlier batches |
| Microbe functions | Convert milk sugar lactose to lactic acid, break down proteins, contribute to flavor and texture, produce holes in cheese |
| Adjunct microbes | Lactobacillus helveticus, Non-Starter Lactic Acid Bacteria (NSLAB) |
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What You'll Learn
Bacteria, yeast, and moulds
Bacteria, yeasts, and moulds are all microorganisms that play a crucial role in the cheesemaking process, contributing to the unique flavours, textures, and characteristics of different cheeses.
Bacteria
Bacteria are the most commonly used microbes in cheesemaking. They can be broadly classified into two groups: Mesophilic bacteria, which thrive at room temperature but die at higher temperatures, and Thermophilic bacteria, which thrive at higher temperatures (around 55°C). Mesophilic bacteria are used in cheeses such as cottage cheese, while Thermophilic bacteria are used in sharper cheeses like Gruyère, Parmesan, and Romano.
One of the primary functions of bacteria in cheesemaking is to convert lactose (milk sugar) into lactic acid, lowering the pH of the milk and creating an environment inhospitable to spoilage organisms. This process is often initiated by "'starter' bacteria", which can be naturally occurring in milk or specifically chosen for cheesemaking as industrial starter cultures. Lactobacillus helveticus, for example, gives aged Gouda its pleasant sweet flavour and promotes tyrosine crystal growth.
Other notable bacteria include Brevibacterium linens, responsible for the distinctive smell of many surface-ripened cheeses, and Propionibacter shermanii, which can convert acetic acid into sharp-smelling propionic acid and carbon dioxide, giving Swiss cheeses like Emmental their characteristic holes.
Yeast
Yeasts are commonly used in moulded and surface-ripened cheeses. They contribute to the unique textures and flavours of these cheeses. One notable example is Geotrichum candidum, a yeast with mould-like tendencies that give some cheeses a "brainy" appearance.
Moulds
Moulds are filamentous fungi that play a significant role in the cheesemaking process, especially in natural rind cheeses. They interact with bacteria and yeast to create the complex flavours and characteristics of certain cheeses. Mould-ripened cheeses like Camembert have fuzzy rinds, while blue-veined cheeses like Cabrales and Roquefort are known for their distinctive marbling.
Moulds can be introduced intentionally or develop naturally during the ageing process. The development of moulds can be encouraged by specific environmental conditions, such as temperature and humidity control.
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Microbial CSI
Microbes are essential to the process of cheesemaking. They are responsible for the unique flavours, textures, and aromas of the thousands of cheese varieties produced worldwide. The broad groups of cheesemaking microbes include bacteria, yeasts, and filamentous fungi (molds).
The study of microbes in cheese involves examining the microbial ecosystems within different cheeses. Scientists like Ben Wolfe, a microbial ecologist at Tufts University, investigate the bacteria and fungi present in cheese by sampling cheeses from around the world and extracting and identifying their DNA. This process has been likened to a "microbial CSI", as scientists delve into the complex world of microorganisms within cheese.
Cheese is a dairy product that is coagulated from milk proteins, specifically the protein casein. During cheesemaking, milk is usually acidified, and enzymes or bacterial enzymes are added to coagulate the milk. The milk separates into solid curds and liquid whey, which is drained away. The curds are then salted, shaped, and left to ripen in a controlled environment. Microorganisms play a crucial role in each step, influencing the final flavour and texture of the cheese.
The milk sugar lactose is broken down into lactic acid by a group of bacteria called lactic acid bacteria (LAB). These bacteria, often referred to as starter cultures, lower the pH of the milk, inhibiting the growth of spoilage organisms. There are two main families of lactic acid bacteria: lactococci (sphere-shaped) and lactobacilli (rod-shaped). Streptococci also play a role in initial cheese ripening.
In addition to these bacteria, other microbes contribute to the unique characteristics of cheese. For example, Propionobacter shermanii is found in alpine and Italian hard cheeses. This bacterium can digest acetic acid, converting it into propionic acid and carbon dioxide. The carbon dioxide creates the characteristic "holes" in cheeses like Emmental, while the propionic acid contributes to their sharp aroma.
Cheese also provides a habitat for microbes that are intentionally introduced or naturally present during the aging process. Traditional cheesemaking often involves allowing microbes from the aging room to settle and grow on the stored cheeses. These can include yeasts and molds, which contribute to the distinctive fuzzy rinds of certain cheeses. Washed-rind cheeses, such as Limburger, are known for their strong odour, produced by microbes like B. linens, which break down proteins into odorous compounds.
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Microbial ecosystems
Cheese is a dairy product with a wide range of flavours, textures, and forms, produced by coagulating milk proteins and separating them into solid curds and liquid whey. The solid curds are then pressed into the finished cheese product. The process involves microorganisms at every step, with bacteria, yeasts, and moulds contributing to the unique characteristics of different cheeses.
Cheese is often described as a microbial ecosystem, with each slice containing billions of microbes. These microbes interact with each other and their environment, creating a complex society within the cheese. The variety of microbes found in cheese is vast, with over 100 different microbial species found in a single cheese type. The specific combination of microorganisms is what gives each cheese its distinct character and flavour.
The microbes in cheese can come from various sources. In traditional cheesemaking, microbes might be present in the ageing room or introduced through the sea salt used in the brine. Some cheesemakers hold back part of the whey from a batch of cheese to use as a starter culture for the next batch, a process called backslopping. This method has been used for centuries, with the microbes adapting to their dairy environment over time. Modern cheesemaking often involves the use of pure microbial cultures, which has led to more standardised cheese production.
Lactic acid bacteria, or "starter cultures", play a crucial role in converting milk sugar (lactose) into lactic acid, lowering the cheese's pH and inhibiting the growth of spoilage organisms. There are two main families of lactic acid bacteria: lactococci (sphere-shaped) and lactobacilli (rod-shaped). Other microbes, such as Brevibacterium linens, are responsible for the distinctive odour of certain cheeses, producing compounds that give rise to strong aromas.
The addition of microbes is not limited to producing lactic acid. Adjuncts, such as Lactobacillus helveticus, are added to encourage flavour development and contribute to the unique characteristics of different cheeses. As cheese ages, the microbial composition continues to evolve, with Non-Starter Lactic Acid Bacteria (NSLAB) increasing in number while starter cultures die off. This dynamic microbial ecosystem is what gives cheese its distinctive and delicious qualities.
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Adjuncts and non-starters
Adjuncts are microbes added to cheese for reasons other than producing lactic acid. They are often used to encourage flavour development. Common adjuncts include Lactobacillus helveticus, Lactobacillus casei, Leuconostoc mesenteroides subsp. cremoris, and Geotrichum candidum. Lactobacillus helveticus, for example, often gives a sweet flavour to cheeses like aged gouda.
Adjuncts are added at low levels to the starter or separately to the milk in the vat, leading to enhanced flavour development and increased control over the nature of that flavour. They are also added because they produce antimicrobial substances called bacteriocins that inhibit other organisms that may be present in cheese.
Non-starter lactic acid bacteria (NSLAB) are lactic acid bacteria that grow as cheese is ripened but weren't added for the express purpose of acidifying the milk. They are present naturally in the milk or are picked up during cheesemaking. As cheese ages, the number of NSLAB increases while starter cultures die off. Their exact role in cheese flavour development is still being understood.
The secondary flora of non-starter microorganisms may be added in the form of defined cultures or may be composed of adventitious microorganisms that gain access to the cheese from ingredients or the environment. They contribute significantly to the specific characteristics of a particular variety of cheese.
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Marine microbes
Cheese is a dairy product made from milk that is chemically altered using bacteria and mould microbes. While all cheesemaking follows the same general process, each type of cheese gets its distinct flavour, texture, and colour based on the different species of bacteria or mould used to create it.
There are a great number of cheese varieties, reflecting the versatility of the microorganisms used in cheese-making. The broad groups of cheese-making microbes include many varieties of bacteria, yeast, and filamentous fungi (moulds).
Some of the most common bacteria used in cheese are lactic acid bacteria, which are used to curdle the milk, creating lactic acid. Non-starter lactic acid bacteria are those that grow as cheese is ripened and are not added for the express purpose of acidifying the milk. Instead, they are present naturally in the milk or are picked up during the cheesemaking process. As cheese ages, the number of NSLAB increases while starter cultures die off.
Cheese is one of the few foods that contains extraordinarily high numbers of living, metabolising microbes. A single gram of the rind of good cheese contains 10 billion microbial cells, a mix of bacteria and fungi that contribute to its flavour.
Recent research has found that marine microbes are also present in cheese. For example, Pseudoalteromonas, a genus of marine bacteria, has been found to produce a great number of flavour compounds, including esters, ketones, and sulfur compounds, which impart fruity, mouldy, and oniony flavours in cheese. Another example is Halomonas, a genus of bacteria usually associated with salt ponds and marine environments, which may get into the cheese via the sea salt in the brine that cheesemakers use to wash down their cheeses.
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Frequently asked questions
Microbes are microscopic living organisms. Bacteria, yeasts, and moulds are the three primary groups of cheese-making microbes. They are responsible for the unique flavours and textures of cheese.
Some common microbes used in cheese include Lactobacillus helveticus, Brevibacterium linens, Geotrichum candidum, and Propionobacter shermanii.
Microbes break down proteins in cheese, releasing various highly flavoured molecules. Different microbes produce different flavour compounds, resulting in the diverse flavours of cheese.
Cheesemakers can control the types and amounts of microbes in cheese by using prepared cultures, adjusting temperature and humidity, and choosing specific ingredients.
