Patrick Oconnell
Cheese is an ecosystem, teeming with bacteria, yeasts, and moulds. In fact, a single slice of cheese can contain billions of microbes, and a single type of cheese can contain over 100 different microbial species. Some of the most important fungi that grow on cheese include Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma. For certain cheeses, such as Camembert and Roquefort, moulds are added intentionally. However, some fungal species can produce undesirable metabolites such as mycotoxins, which pose a food safety problem and can lead to significant economic losses for the cheese industry.
| Characteristics | Values |
|---|---|
| Fungi growing on cheese | Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma |
| Cheeses with intentionally added moulds | Camembert, Roquefort |
| Hazardous mycotoxins found in cheese | Ochratoxin A, Aflatoxin M1 |
| Mycotoxins produced by unwanted fungal species | Via direct cheese contamination or indirect milk contamination |
| Number of different kinds of bacteria and fungi in long-ripened cheeses like Roquefort | Hundreds, sometimes more than 400 |
| Microbial count in a fully ripened cheese | 10 billion bacteria, yeasts, and other fungi per gram of rind |
| Fungal mold seen in Tomme de Savoie cheese | Mucor lanceolatus |
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What You'll Learn
Types of fungus used in cheese
Cheese is an ecosystem, teeming with billions of bacteria, yeasts, and fungi. These microbes are what make each type of cheese distinctive and delicious. In fact, some cheeses contain more than 400 different kinds of bacteria and fungi!
The earliest evidence of cheesemaking dates back to the 6th century in Poland, where only lactic acid bacteria (LAB) were added to fresh milk to promote curdling. Since then, mechanical advancements and experimentation with different fungal species have resulted in the wide variety of cheeses available today.
One of the most well-known fungi used in cheesemaking is Penicillium, specifically the species Penicillium camemberti. This fungus is responsible for the main flavour and odour, soft texture, and white crust of popular cheeses such as Camembert, Brie, Langres, Coulommiers, and Cambozola. It is also used to flavour other foods, such as dry, fermented sausages.
Other important fungi in cheesemaking include Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma. Some cheeses, like Camembert and Roquefort, intentionally add moulds to develop their flavour. However, some fungal species can be undesirable, as they may produce harmful mycotoxins or impart a bitter taste if their concentration is too high.
Fungi play a critical role in the creation of cheese, influencing its texture, flavour, and overall character. The specific fungi present in a cheese depend on how it is made, ripened, and the variety it is.
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How fungus and bacteria work together
Cheese is an ecosystem, teeming with bacteria, yeasts, and moulds. In fact, a single slice of cheese can contain billions of microbes, and a single type of cheese can contain over 100 different microbial species. These microbes are what make each cheese distinctive and flavourful.
Fungi and bacteria work together in cheese in a number of ways. Firstly, bacteria can use the fungal network to spread and grow. The fungi's microscopic, branched tendrils, known as hyphae, provide highways for bacterial swimmers to get around and travel far and wide. This intermingling of fungi and bacteria creates a complex and tasty cheese. For example, the bacteria Serratia proteamaculans, which gives cheese a note of cooked cabbage, can be found alongside fuzzy tufts of Mucor lanceolatus mould.
However, from a microbial standpoint, the cooperation between fungi and bacteria is not always beneficial. Both entities require the same ingredients to survive – water and nutrients – and when resources are scarce, they employ strategies to outcompete one another. For example, fungal moulds create chemicals to burst bacteria open, which have been used by humans to create antibiotics like penicillin. On the other hand, bacteria have specialised enzymes, called chitinases, that liquify fungi, turning them into a slurry of carbon and nitrogen.
Despite this competition, fungi and bacteria have been "domesticated" by cheesemakers over centuries of cheesemaking. Cheesemakers in Switzerland, for example, use the traditional method of backslopping, where a part of the whey from a batch of cheese is held back and used again when making the next batch. Over time, the backslopped microbes have lost genes that are no longer useful for them in their specialised dairy environment, such as genes needed to metabolise non-lactose sugars.
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The dangers of fungus in cheese
While mould is a key ingredient in many types of cheese, certain fungal species can be harmful. Some undesirable fungi can produce mycotoxins, which are toxic metabolites. The most hazardous mycotoxins found in cheese include ochratoxin A, aflatoxin M1, cyclopiazonic acid, and sterigmatocystin. These toxins can contaminate cheese directly or indirectly through milk or animal feed. Although no human food poisoning cases have been linked to contaminated cheese consumption, these toxins have been detected in cheeses at varying concentrations.
The main source of mould contamination in cheese production facilities is the environment, particularly the air and surfaces in the plant. To prevent the spread of problem moulds, visible mould growth on cheese should be avoided. Proper identification of the contamination source is necessary to implement effective control measures.
When consuming cheese with mould, it is generally safe to cut away or scrape off the mouldy parts for most types of cheese. However, it is important to assess the type of cheese and the extent of mould growth. Fresh soft cheeses, such as ricotta, mascarpone, and chèvre, should be discarded if mould is present, as it is likely to have penetrated deeply and negatively affected the flavour. For soft cheeses like Brie or Camembert, a quarter-inch layer should be cut away from any mouldy surfaces. Harder, aged cheeses like Cheddar or Parmesan can have the mould scraped off.
It is worth noting that the stomach's acidic environment can kill mould spores, so consuming a small amount of mould is usually not harmful. However, it is always recommended to store cheese properly and consume it within a reasonable timeframe to prevent excessive mould growth. Overall, while some moulds in cheese are desirable and contribute to its unique flavour, others can pose potential health risks, and it is important to handle and consume mouldy cheese with caution.
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How fungus impacts the taste of cheese
The presence of fungus significantly impacts the taste of cheese. Fungi, along with bacteria and yeasts, are part of the cheesemaking process and contribute to the flavour and texture of the final product. While some types of fungus are intentionally added to certain cheeses, other types of fungus can unintentionally contaminate the cheese, altering its taste and making it unsafe for consumption.
Fungus plays a crucial role in the development of flavour in cheese. During the cheesemaking process, fungi interact with bacteria, creating a complex microbial ecosystem. This interplay between fungi and bacteria leads to the production of various flavours and aromas, resulting in a more nuanced and tasty cheese. For example, the fungus Mucor lanceolatus, which grows on Tomme de Savoie cheese, does not have a strong taste itself. However, it provides a structure for more flavourful bacteria to travel along, contributing to the overall flavour profile of the cheese.
Different types of fungi can impart distinct flavours to the cheese. For instance, the slow-growing fungal mold Penicillium has an earthy taste reminiscent of mushrooms, with a hint of damp basement. On the other hand, the choice of bacterial species, such as Serratia proteamaculans, can give cheese a unique note of cooked cabbage. The combination of these fungal and bacterial flavours creates a diverse and appealing taste profile in the final cheese product.
While some fungi are desirable in cheesemaking, other types of fungus can be detrimental. Unwanted fungal species, such as Aspergillus niger, can contaminate cheese and produce undesirable metabolites called mycotoxins. Mycotoxins not only negatively impact the flavour and texture of the cheese but also pose potential health risks. Ochratoxin A and aflatoxin M1 are two of the most hazardous mycotoxins found in contaminated cheese, which can enter the cheese through direct contamination or indirect milk contamination from animal feed. Therefore, it is essential to prevent the growth of problem moulds during cheese production to maintain both the quality and safety of the cheese.
In summary, fungus plays a critical role in shaping the taste of cheese. The presence of specific fungal species, their interaction with bacteria, and the production of various metabolites all contribute to the flavour profile of the final cheese product. While some fungi are intentionally added to develop desirable flavours, it is crucial to control and prevent the growth of unwanted fungal contaminants to ensure the safety and quality of the cheese.
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How to identify fungus contamination
While the presence of fungi is essential to the production of some cheeses, it can also be a source of contamination. Mould growth on cheese can cause quality and food safety issues and result in significant economic losses for cheese producers.
To identify fungus contamination, it is necessary to look out for visible mould growth on the cheese. This may appear as a change in texture or colour, such as a white rind or darkly mottled surface. If mould is visible, it is important to avoid consuming the cheese, as it may be a sign of further contamination.
In addition to visual inspection, other methods can be employed to identify specific fungal species. For example, phenotypic and genotypic tactics can be used to identify fungal isolates. This involves the sequencing of taxonomically related target genes, allowing for the precise identification of the fungus. Another method is to examine the microbial population by sampling and extracting the DNA of the cheese to determine the presence of specific bacteria and fungi.
To prevent fungus contamination, it is crucial to maintain good hygiene practices and implement production controls. This includes regular cleaning and disinfection of equipment and facilities, as well as the occasional examination of the microbiological population to identify potential risks associated with toxin-producing species. By following these practices, cheese producers can ensure the safety of their products and reduce the risk of economic losses due to fungus contamination.
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Frequently asked questions
Some examples of fungus used in cheese are Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma.
Fungi can end up in cheese through various means. For some cheeses, fungi are intentionally added, as in the case of Camembert and Roquefort. In other cases, fungi can be introduced via the brine that cheesemakers use to wash their cheeses.
Fungi play a crucial role in the cheese-making process by contributing to the distinct flavours and characteristics of different cheeses. The interaction between fungi and bacteria creates a complex and tasty cheese.
While fungi are essential for the production of certain cheeses, they can also pose a food safety problem. Some fungal species may produce mycotoxins, such as ochratoxin A, cyclopiazonic acid, and sterigmatocystin, which can be hazardous even under normal processing conditions.
