Frederic Melton
Swiss cheese is known for its pale yellow hue, firm yet creamy texture, and nutty, mellow, slightly sweet flavour. Its most recognisable feature, however, is the holes scattered across its surface, which are created by the action of bacteria. Propionibacterium freundenreichii is a specific bacterium that converts lactic acid into carbon dioxide, propionic acid, and acetic acid. The carbon dioxide seeps into the cheese body and produces the holes, or eyes, that Swiss cheese is famous for. Lactobacillus helveticus is another culture commonly used in Swiss and alpine cheeses, often giving cheeses a sweet flavour.
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What You'll Learn
- The holes in Swiss cheese are caused by bacteria
- Propionibacterium freudenreichii ferments lactate to create carbon dioxide, propionic acid, and acetic acid
- Lactobacillus helveticus is a culture commonly used in Swiss cheese
- Non-starter lactic acid bacteria (NSLAB) contribute to the flavour of Swiss cheese
- The length of ripening varies from two weeks to over two years
The holes in Swiss cheese are caused by bacteria
Swiss cheese is easily recognizable for its pale yellow hue, firm yet creamy texture, and scattered holes. These holes, or "eyes", are the result of bacteria that create carbon dioxide during the cheese's ripening process.
Propionibacterium freudenreichii, or Propionibacterium freundenreichii, is a specific bacterium that converts lactic acid into carbon dioxide, propionic acid, and acetic acid. The carbon dioxide seeps into the body of the cheese and forms the eyes. The propionate and acetate produced by this bacterium also contribute to the characteristic sweet and nutty flavor of Swiss cheese.
The size of the eyes in Swiss cheese is influenced by various factors, including the aging time, acid content, and temperature during production. Generally, longer aging results in larger eyes, and the eyes in traditional Swiss cheese are cherry to walnut-sized. Swiss cheese manufactured in the US tends to have smaller eyes due to a shorter aging process.
Other bacteria, such as Lactobacillus helveticus, also play a role in the flavor development of Swiss cheese. Lactobacilli are commonly used as adjuncts, which are microbes added to enhance flavor. Lactobacillus helveticus, in particular, contributes a pleasant sweet flavor and promotes the growth of tyrosine crystals.
The presence of bacteria in Swiss cheese is not only responsible for its unique appearance but also offers potential health benefits. Swiss cheese is an excellent source of calcium and protein and has lower sodium content compared to other cheeses. Additionally, it contains low levels of the enzyme commonly found in dairy products, making it more suitable for individuals with lactose intolerance.
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Propionibacterium freudenreichii ferments lactate to create carbon dioxide, propionic acid, and acetic acid
Propionibacterium freudenreichii is a Gram-positive, rod-shaped bacterium that is commonly used as an adjunct starter in Swiss-type cheeses, such as Emmental and Maasdam. This bacterium plays a crucial role in the ripening process of Swiss cheese, fermenting lactate to create carbon dioxide, propionic acid (propionate), and acetic acid (acetate).
During the ripening process, Propionibacterium freudenreichii grows and metabolizes lactate, resulting in the production of these three compounds. The carbon dioxide forms the distinctive "eyes" or holes in Swiss cheese. As the cheese ages, the "eyes" become larger, and the size can also be influenced by factors such as acid content and temperature. The propionic and acetic acids contribute to the characteristic sweet and nutty flavor of Swiss cheese.
Propionibacterium freudenreichii is particularly effective in cheese ripening due to its ability to tolerate different oxygen levels, ranging from anaerobic to aerotolerant conditions. Additionally, it has optimal growth conditions at temperatures of 25–32 °C and a pH range of 6.5–7.0. These factors make it well-suited for the cheese-making environment.
The use of Propionibacterium freudenreichii in cheese production has a long history, and it is considered safe for human consumption. While it is primarily known for its role in Swiss cheese, this bacterium also has other applications. For example, it has been used in the production of vitamin B12, although its use has partially been replaced by Pseudomonas denitrificans due to faster growth and higher yields.
In conclusion, Propionibacterium freudenreichii is a crucial bacterium in the production of Swiss cheese. Its ability to ferment lactate and produce carbon dioxide, propionic acid, and acetic acid gives Swiss cheese its distinctive appearance and flavor. The understanding and utilization of this bacterium have contributed significantly to the art of cheesemaking.
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Lactobacillus helveticus is a culture commonly used in Swiss cheese
L. helveticus is a ubiquitous bacterial species in natural whey cultures (NWCs) used for Swiss Gruyère cheese production. It is considered to have crucial functions for cheese ripening, such as enhancing proteolysis. The core microbiome of these cultures is formed by Lactobacillus helveticus, Streptococcus thermophilus, and Lactobacillus delbrueckii subsp. lactis.
L. helveticus is also commonly used as an adjunct in Swiss and alpine cheeses. Adjuncts are microbes that are added for reasons other than just producing lactic acid. They are often added to encourage flavour development in the cheese. L. helveticus often gives a sweet flavour to cheeses like aged Gouda and promotes the growth of tyrosine crystals.
The relative change in pH can indicate the effectiveness of lactobacillus starters in cheese. The growth and action of lactobacillus cultures usually begin an hour or two later in larger cheeses, as the interior cools more slowly. Bacteria of the Lactobacillus casei types usually increase in numbers if present and can attain large numbers under certain conditions.
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Non-starter lactic acid bacteria (NSLAB) contribute to the flavour of Swiss cheese
Non-starter lactic acid bacteria (NSLAB) are lactic acid bacteria that grow as cheese ripens, which were not originally added for the express purpose of acidifying the milk. They are often present naturally in the milk or are picked up during the cheesemaking process. NSLAB dominate the cheese microbiota during ripening, and strongly influence the biochemistry of curd maturation, contributing to the development of the final characteristics of the cheese.
The significance of NSLAB in cheese quality is still controversial, but they have been shown to contribute to the release of amino acids and to influence flavour development. The uncontrolled evolution of NSLAB may lead to variable results in cheese production, so the selection of strains with specific technological characteristics is important to maintain a certain cheese typicality.
In Cheddar cheese, for example, a mixture of Lactobacillus paracasei, Lact. plantarum, Lact. rhamnosus and unidentified strains was found up to 6 weeks of maturation, after which only Lact. paracasei strains were isolated. Little variation in the spatial distribution of NSLAB strains was observed within the Cheddar cheese, but temporal changes in the species and strains were observed during ripening. The complex changes in the composition of the NSLAB community of Cheddar cheese may be the source of the variation in flavour that is seen in commercial practice.
In addition to Cheddar, NSLAB are also found in other cheeses such as Fiore Sardo, Fossa cheese, and other European traditional cheeses. Raw milk is the main source of NSLAB, but they can also come from other cheese-making ingredients and contamination of plant equipment with persistent biofilms.
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The length of ripening varies from two weeks to over two years
The length of time required for cheese ripening varies significantly, ranging from two weeks to over two years. This duration is dependent on various factors, including the type of cheese, the desired flavour profile, and the specific bacteria and microorganisms involved in the ripening process.
For example, Swiss cheese, known for its distinctive holes, undergoes ripening through the activity of bacteria such as Propionibacterium freudenreichii or Propionibacterium freundenreichii. This bacterium converts lactic acid into carbon dioxide, propionic acid, and acetic acid. The carbon dioxide formation contributes to the development of the eyes or holes in Swiss cheese, and the longer the ripening period, the larger these holes tend to be.
The flavour of Swiss cheese is also influenced by the bacteria during the ripening process. Propionibacterium metabolism produces compounds that give Swiss cheese its characteristic nutty and sweet flavour notes. Additionally, adjuncts, or microbes added to enhance flavour development, can further extend the ripening time to achieve the desired taste profile.
The ripening duration is not only critical for flavour development but also plays a role in the texture and overall character of the cheese. For instance, in Camembert-type and Blue cheeses, the development of a complex bacterial flora, including Roqueforti, contributes to both the flavour and the distinctive appearance of these varieties.
The variability in ripening times allows cheesemakers to create diverse products with unique characteristics. While some cheeses benefit from shorter ripening periods, others develop their full flavour and texture potential over more extended periods, showcasing the intricate relationship between time and the microbial activity that transforms milk into cheese.
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Frequently asked questions
Propionibacterium freundenreichii is the bacteria that creates the holes in Swiss cheese. It ferments lactate to acetate, propionate, and CO2. The CO2 produced by this process gets trapped in the cheese, creating the holes.
The bacteria feed on lactic acid, which is converted into carbon dioxide, propionic acid, and acetic acid.
Lactobacilli, such as Lactobacillus helveticus, are commonly used as a starter culture in Swiss cheese. They contribute to flavour development and are often responsible for the sweet taste in Swiss cheese.
