Andy Montoya
Swiss cheese is known for its distinctive holes, which lend the cheese its unique appearance, delightful texture, and slightly nutty taste. The holes, also called eyes, are created by bacteria, carbon dioxide, and culinary artistry. While the presence of holes in Swiss cheese has long been attributed to bacteria, the specific cause has been a subject of debate. Traditionally, it was believed that the holes were formed by carbon dioxide released by bacteria present in the milk. However, recent studies have challenged this theory, suggesting that the holes may be caused by flecks of hay falling into milk buckets during collection or by modern milking methods that prevent hay from contaminating the milk.
| Characteristics | Values |
|---|---|
| Reason for holes in Swiss cheese | The holes in Swiss cheese are caused by bacteria, carbon dioxide, and culinary artistry. |
| Type of bacteria | Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short |
| Function of bacteria | Converts milk into carbon dioxide at warm temperatures of around 70°F (21°C) |
| Hole formation | As the bacteria grow, the emitted gases create round openings. When the cheese is cooled to around 40°F (4°C), the holes remain. |
| Time for hole formation | It takes about four weeks at 70°F for the holes to form |
| Influence on taste and texture | The holes contribute to the cheese's nutty taste and light, airy feel |
| Hole size and distribution | Influenced by temperature, humidity, and fermentation times during the cheese-making process |
| Traditional Swiss cheeses without holes | Gruyère and Emmental |
| Hole size variation | Swiss cheese varieties like Jarlsberg and Appenzeller are known for their different hole sizes |
| Reduction in hole size | Modern milking methods have kept hay out, resulting in smaller holes over time |
| Historical theory | Carbon dioxide released by bacteria present in the milk |
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What You'll Learn
The holes are not caused by mice or rodents
Swiss cheese is known for its distinctive holes, which are called "eyes". The holes are not caused by mice or rodents, as was once believed. In fact, the holes are caused by bacteria and the cheese-making process.
The holes in Swiss cheese are primarily due to a bacterial strain called Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short. This bacterium converts milk into carbon dioxide at warm temperatures of around 70°F (21°C). As the cheese cools, the carbon dioxide is trapped, forming the holes that give Swiss cheese its unique appearance.
The size and distribution of the holes can vary depending on factors such as temperature, humidity, and fermentation times during the cheese-making process. Traditional Swiss cheeses like Emmental and Appenzell tend to have larger holes, while modern Swiss cheeses and those made outside of Switzerland may have smaller holes or none at all.
The presence of holes in Swiss cheese has long been a mystery, with early theories attributing them to carbon dioxide released by bacteria or hungry rodents. However, modern scientific research has dispelled these ideas. In 2015, Agroscope, a Swiss agricultural institute, discovered that the holes are actually caused by flecks of hay falling into milk buckets during the milking process. This finding explained the decrease in hole size observed over the years due to improved milking methods.
So, while the idea of mice nibbling holes in Swiss cheese may have persisted as a charming old wives' tale, the true explanation lies in the fascinating interplay of bacteria, temperature control, and the accidental inclusion of hay particles in the cheese-making process.
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A bacterial strain called Propionibacterium produces carbon dioxide
The holes in Swiss cheese are primarily due to a bacterial strain called Propionibacterium. These are microscopic, gram-positive, non-motile bacteria that create the iconic Swiss cheese bubbles. Propionibacterium takes the lactic acid leftover from other bacteria and converts it into carbon dioxide. This gas gets trapped in the cheese, forming bubbles that we call "holes".
Propionibacterium freudenreichii is a subspecies of Propionibacterium that is commonly associated with cheese. It has two subspecies: Propionibacterium freudenreichii subsp. freudenreichii and Propionibacterium freudenreichii subsp. shermanii. These bacteria can metabolize carbohydrates, polyols, and pyruvate to form propionate, acetate, succinate, and carbon dioxide. They are essential during the cheese ripening process, especially for Swiss cheese, and have been used for centuries to produce its characteristic flavour and "eyes" or holes.
Propionibacterium freudenreichii subsp. shermanii is specifically responsible for converting milk into carbon dioxide at around 70°F (21°C). When the cheese cools, the air bubbles are left behind, creating the holes that Swiss cheese is famous for. This subspecies is also able to ferment lactose, which is why it plays such an important role in cheese production.
The size and distribution of the holes in Swiss cheese are influenced by various factors during the cheese-making process, including temperature, humidity, and fermentation times. For instance, the cheese must have an extremely elastic curd structure and be exposed to high temperatures during the ageing process to activate the bacteria and create the holes.
The presence of these bacteria in Swiss cheese is not accidental. In the past, when cheese was made in the summer and then aged during the winter months in the Swiss Alps, it is believed that the bacteria made its way into the cheese from the grass and flowers consumed by the milking cows. Today, cheesemakers use live cultures to intentionally add these bacteria and create the desired hole structure in Swiss cheese.
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Modern milking methods have reduced the size of the holes
Swiss cheese is known for its distinctive holes, also known as "eyes". These holes are caused by bacteria that help convert the milk into a solid. Specifically, the bacteria Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short, produces carbon dioxide gas, which creates the holes in the cheese. The size and distribution of the holes are influenced by factors such as temperature, humidity, and fermentation times.
Historically, Swiss cheese was made in barns using open buckets, which allowed hay particles to contaminate the milk. These hay particles created weaknesses in the structure of the curd, allowing gas to form and expand, eventually creating the holes. However, with the modernization of dairy farming practices, including the adoption of more automated and antiseptic milking methods, the incidence of hay particles in the milk has decreased.
Modern milking methods prioritize hygiene and the prevention of hay contamination. Milk is now typically extracted using advanced equipment and systems, ensuring that the milk used for cheesemaking is free from foreign particles. These modern techniques have contributed to the reduction in the size and occurrence of holes in Swiss cheese.
One key factor in reducing hole size is the use of sealed containers, pipes, and filters, which minimize the risk of hay contamination. Additionally, modern milking practices often involve temperature control during the cheesemaking process. By adjusting the temperature, cheesemakers can influence the size of the holes. Higher temperatures promote the production of carbon dioxide gas by bacteria, leading to larger bubbles, while cooling the cheese helps stabilize the bubbles and ensures they remain in place during aging.
While the reduction in hole size may be seen as a positive development by some, others may view it as a loss of the traditional characteristics of Swiss cheese. The presence of holes has long been associated with the unique identity of Swiss cheese, and their gradual disappearance could be seen as a departure from the classic cheese-making process.
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The size and distribution of holes are influenced by temperature, humidity, and fermentation
The holes in Swiss cheese are caused by a specific strain of bacteria, Propionibacterium freudenrichii subspecies shermanii, which releases carbon dioxide at warm temperatures of around 70°F (21°C). As the cheese cools, the gas becomes trapped, forming bubbles that create the holes. The size and distribution of these holes are influenced by various factors during the cheese-making process, including temperature, humidity, and fermentation times.
Temperature plays a crucial role in the formation of Swiss cheese holes. The ideal temperature for the bacteria to produce carbon dioxide and for the cheese to remain soft and pliable is around 70°F. At this temperature, the bacteria can grow and emit gases, forming round openings in the cheese. Once the cheese is cooled to around 40°F, the holes are set in place.
Humidity also impacts the hole formation process. While high humidity can affect the texture and quality of cheese, it is unclear exactly how it influences the size and distribution of holes. However, it is known that the interaction between humidity and temperature is essential for the growth of the Propionibacterium bacteria and the production of carbon dioxide.
Fermentation is another key factor. Swiss cheese undergoes propionic acid fermentation, which produces aromatic carbon dioxide bubbles. To activate this process, the cheese must have an extremely elastic curd structure and be subjected to a high-temperature stage during aging. Traditionally, this occurred when cheese made during the summer was aged near a hearth in the winter months in the Swiss Alps. The specific conditions of temperature and humidity during this aging process influence the fermentation and, consequently, the size and distribution of holes.
Additionally, the size and distribution of holes can vary depending on the specific variety of Swiss cheese. For example, Jarlsberg is known for its medium-sized holes, while Appenzeller has larger holes. These differences are due to variations in the cheese-making process, including the specific temperatures, humidity levels, and fermentation times employed.
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Swiss cheese holes are called eyes
Swiss cheese is easily recognizable for its holes, which are called "eyes". The holes are not the result of mice eating through the cheese, as cartoons have often suggested, but rather a product of the cheese-making process.
The holes in Swiss cheese are primarily caused by a specific bacterial strain called Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short. This bacterium converts lactic acid into carbon dioxide at warm temperatures of around 70°F (21°C). As the bacteria grow, they emit gases that become trapped in the cheese, forming bubbles that create the eyes. When the cheese is cooled to around 40°F (4°C), the holes remain, giving Swiss cheese its distinctive appearance.
The size and distribution of the eyes in Swiss cheese can vary depending on factors such as temperature, humidity, and fermentation times during the cheese-making process. Different varieties of Swiss cheese, such as Jarlsberg and Appenzeller, are known for their unique characteristics, with Jarlsberg having medium-sized holes and Appenzeller boasting larger ones.
While the role of bacteria in hole formation was long believed to be the result of carbon dioxide release, modern science has offered alternative explanations. In 2015, researchers from Agroscope, a Swiss agricultural institute, proposed that the holes were caused by microscopically small hay particles falling into milk buckets during collection. This theory was supported by experiments adding hay dust to milk and observing hole development over time. The reduction in hole sizes over the years has been attributed to improved milking methods that minimize hay contamination.
Swiss cheese, also known as Emmental cheese, originated in the Emmental region of Switzerland in the 14th century. It is traditionally made with raw cow's milk, though modern variations may use pasteurized or part-skim milk. The cheese is classified with geographical indications, requiring specific ingredients, shapes, and aging processes to bear the Emmental name.
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Frequently asked questions
No, the holes in Swiss cheese are not caused by mould. They are caused by a specific bacteria called Propionibacterium freudenrichii subspecies shermanii, which converts milk into carbon dioxide at warm temperatures.
Propionibacterium freudenrichii subspecies shermanii, or P. shermanii, produces carbon dioxide gas at warm temperatures. This gas gets trapped in the cheese, forming bubbles that create the holes in Swiss cheese.
Yes, various factors such as temperature, humidity, and fermentation times influence the size and distribution of the holes. The cheese-making process, including the specific conditions under which Swiss cheese is crafted, also plays a role in hole formation.
Modern milking methods have improved hygiene, reducing the amount of hay dust and dirt that falls into milk buckets. This has resulted in fewer and smaller holes in Swiss cheese over the years.
