Frederic Melton
Swiss cheese is known for its distinctive holes, which are called eyes. When the holes don't appear, cheesemakers say the batch is blind. The eyes 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. Interestingly, the holes have become smaller or non-existent in recent years due to the use of modern milking methods, which prevent hay particles from falling into the milk and creating weak points in the curd structure where gas can form and create the holes.
| Characteristics | Values |
|---|---|
| Reason for holes | Tiny bits of hay in the milk, bacteria cultures producing carbon dioxide gas, temperature, humidity, and fermentation times |
| Bacteria involved | Propionibacterium freudenrichii subspecies shermanii (P. shermanii) |
| Formation time | Around four weeks at 70°F |
| Total time to make | Six weeks, then aged for two months |
| First made | 15th century in Switzerland |
| Other names | Emmentaler, Emmental, Swiss Cheese |
| Hole size | Varies, with some having small eyes and others larger holes |
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What You'll Learn
The role of microbes and bacteria
Now, when it comes to Swiss cheese, a particular bacterial strain, Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short, is the key player in creating those distinctive holes, also charmingly known as "eyes." This additional bacterium produces carbon dioxide gas under the specific conditions Swiss cheese is made in, particularly the warm temperature of around 70 degrees Fahrenheit.
As the P. shermanii bacteria feast on the lactic acid present in the cheese, they release carbon dioxide. This gas forms bubbles or air pockets within the soft and malleable cheese mass. As the cheese then cools down to around 40°F, these bubbles solidify, resulting in the formation of the eyes. It takes about four weeks at 70°F for these holes to form, and the entire process of making Swiss cheese takes about six weeks, followed by two months of ageing.
The size and distribution of the holes in Swiss cheese are influenced by various factors, including temperature, humidity, and fermentation times. Different varieties of Swiss cheese, such as Jarlsberg and Appenzeller, are known for their unique hole sizes and flavours. Interestingly, the traditional method of collecting milk in open buckets allowed tiny bits of hay to fall into the milk, creating weaknesses in the curd structure and facilitating the formation of holes. However, with modern milking methods, this is less common, leading to fewer holes in Swiss cheese in recent years.
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Carbon dioxide gas
The holes in Swiss cheese, also known as "eyes", are caused by carbon dioxide gas. This gas is released by bacteria present in the milk, specifically a bacterium called Propionibacterium shermanii or Propionibacter shermani, which is used for the ripening of Swiss cheese. During the cheese-making process, this bacterium consumes lactic acid, which is then converted into propionic acid and carbon dioxide. The carbon dioxide forms bubbles, which create the holes in the cheese. The size of the holes can vary, and larger holes indicate a more intense and developed flavor.
The presence of this bacterium is essential for the formation of eyes in Swiss cheese. It is a type of bacteria that is naturally found in hay, grasses, and soil, and it can make its way into raw milk when cows are milked. However, the pasteurization process kills this bacterium, so if pasteurized milk is used as the base for Swiss cheese, cheesemakers add it back in to ensure the formation of eyes.
After the Swiss cheese is made and brined, the blocks or wheels are placed in warm rooms. This step aids in the production of carbon dioxide by the bacterium and helps maintain the desired consistency of the cheese. The warm environment promotes the metabolic activity of the bacterium, leading to increased carbon dioxide production.
The relationship between the flavor and the size of the eyes is intriguing. The larger the holes in the cheese, the more intense and mature the flavor. This correlation is attributed to the increased presence of flavor-enhancing bacteria in aged cheese. This may explain the variation in taste between American-produced Swiss cheese, known for its smaller air pockets, and its European counterparts, which tend to have larger eyes and richer, nuttier flavors.
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Temperature, humidity, and fermentation
The process of making Swiss cheese involves warming the cheese to a temperature of around 70°F (21°C). This temperature is crucial as it softens the cheese, making it more pliable and susceptible to the formation of holes. At this temperature, the additional bacteria Propionibacterium freudenrichii subspecies shermanii (P. shermanii) produce carbon dioxide gas. As the bacteria grow and emit gas, they create round openings in the soft, warm cheese.
During the fermentation process, the bacteria consume lactic acid in the cheese and produce carbon dioxide as a byproduct. This gas forms air pockets within the cheese, which eventually become the holes. The specific conditions of temperature and humidity during fermentation influence the size and distribution of these air pockets, resulting in the unique hole pattern of Swiss cheese.
After the bubbles have formed inside the warm cheese, the cheese is then cooled to around 40°F (4°C). This cooling process helps to set the holes in place, creating the characteristic "eyes" of Swiss cheese. It takes about four weeks at 70°F for the eyes to form, and the cheese is then aged for an additional two months before being sold.
The traditional method of cheese-making, which involved collecting milk in open buckets, allowed for the presence of tiny bits of hay or dirt, which created weaknesses in the curd structure. This, combined with the specific temperature and humidity conditions, facilitated the formation of the holes. Modern methods of milk extraction have reduced the occurrence of hay particles, resulting in fewer holes in Swiss cheese today.
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Hay particles in milk
Swiss cheese is known for its distinctive holes, also called "eyes". When the holes are missing, cheese makers say the batch is "blind". The eyes are caused by tiny bits of hay present in the milk, according to researchers from Agroscope, a Swiss agricultural institute.
When cheese is made in barns using open buckets, it is likely that hay particles will find their way into the collected milk. These hay particles create weaknesses in the structure of the curd, allowing gas to form and create holes. The size and distribution of the holes are influenced by factors such as temperature, humidity, and fermentation times.
In 1917, William Clark proposed that Swiss cheese holes were caused by carbon dioxide released by bacteria present in the milk. However, this theory was disproven in 2015 by Agroscope researchers, who discovered that the holes were actually caused by hay particles. The disappearance of traditional buckets used during milking has also contributed to the reduction in hole size or their absence in modern Swiss cheese.
Swiss cheese is made with cow's milk and contains bacteria that help convert the milk into a solid. The additional bacteria, Propionibacterium freudenrichii subspecies shermanii, or P. shermanii for short, produce carbon dioxide gas under the specific conditions that Swiss cheese is made. The warm temperature of around 70 degrees Fahrenheit softens the cheese, and as the bacteria grow, the emitted gases create round openings.
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Modern milking methods
However, with the introduction of modern milk extraction techniques, the incidence of hay contamination has decreased, leading to smaller and fewer holes in Swiss cheese over time. This change in milk collection methods has been a key factor in reducing the size and number of holes.
Today's 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 not only improved the consistency and quality of the milk but also contributed to the gradual reduction in the size and occurrence of holes in Swiss cheese.
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, typically around 22°C, promote the production of carbon dioxide gas by bacteria, leading to the formation of larger bubbles that become the characteristic holes in Swiss cheese. On the other hand, cooling the cheese to around 4°C helps stabilize the bubbles and ensures they remain in place during the aging process.
While the specific techniques may vary, modern milking methods share a common goal of producing high-quality milk while adhering to stringent hygiene standards. These methods have not only improved the overall cheesemaking process but also inadvertently influenced the size and prevalence of holes in Swiss cheese.
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Frequently asked questions
The holes in Swiss cheese, also known as "eyes", are caused by tiny bits of hay present in the milk, according to researchers from Agroscope, a Swiss agricultural institute. The hay particles cause a weakness in the structure of the curd, allowing gas to form and create the holes.
The holes in Swiss cheese are called "eyes". When Swiss cheese does not have any holes, it is known as "blind".
Swiss cheese is made with cow's milk and contains bacteria that help convert the milk into a solid. The holes are formed due to additional bacteria called Propionibacterium freudenrichii subspecies shermanii, which produce carbon dioxide gas. As the bacteria grow, the gases they emit create round openings in the cheese.
