Eyes are the round holes that are a characteristic feature of Swiss-type cheese [1] (e.g. Emmentaler cheese) and some Dutch-type cheeses. The eyes are bubbles of carbon dioxide gas. The gas is produced by various species of bacteria in the cheese. [2]
In Swiss-type cheeses, the eyes form as a result of the activity of propionic acid bacteria ( propionibacteria ), notably Propionibacterium freudenreichii subsp. shermanii. [3] [4] These bacteria transform lactic acid into propionic acid and carbon dioxide, according to the formula:
The CO2 so produced accumulates at weak points in the curd, where it forms the bubbles that become the cheese's eyes. [3] Not all CO2 is so trapped: in an 80 kg (180 lb) cheese, about 20 L of CO2 remain in the eyes, while 60 L remain dissolved in the cheese mass and 40 L are lost from the cheese. [1]
In Dutch-type cheeses, the CO2 that forms the eyes results from the metabolisation of citrate by citrate-positive ("Cit+") strains of lactococci. [1]
The citric acid cycle—also known as the Krebs cycle, Szent-Györgyi-Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The chemical energy released is available under the form of ATP. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.
Swiss cheese is any variety of cheese that resembles Emmental cheese, a yellow, medium-hard cheese that originated in the area around Emmental, Switzerland. It is classified as a Swiss-type or Alpine cheese. Some types of Swiss cheese have a distinctive appearance, as the blocks or rounds of the cheese are riddled with holes known as "eyes". Swiss cheese without eyes is known as "blind".
Propionic acid is a naturally occurring carboxylic acid with chemical formula CH
3CH
2CO
2H. It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH
3CH
2CO−
2 as well as the salts and esters of propionic acid are known as propionates or propanoates.
Jarlsberg is a mild cheese made from cow's milk, with large, regular eyes, originating from Jarlsberg, Norway. It is produced in Norway, as well as in Ireland and the US state of Ohio, licensed from Norwegian dairy producers. It is classified as a Swiss-type cheese.
Kashkaval is a type of cheese made from cow's milk, sheep's milk or both. In Albania, Bulgaria, Kosovo, North Macedonia, Romania and Serbia, the term is often used to refer to all yellow cheeses. In English-language menus in Bulgaria, kashkaval is translated as "yellow cheese".
Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight.
Cheesemaking is the craft of making cheese. The production of cheese, like many other food preservation processes, allows the nutritional and economic value of a food material, in this case milk, to be preserved in concentrated form. Cheesemaking allows the production of the cheese with diverse flavors and consistencies.
Emmental, Emmentaler, or Emmenthal is a yellow, medium-hard cheese that originated in Emmen, Switzerland. It is classified as a Swiss-type cheese.
Propionibacterium is a gram-positive, anaerobic, rod-shaped genus of bacteria named for their unique metabolism: They are able to synthesize propionic acid by using unusual transcarboxylase enzymes.
Calcium lactate is a white crystalline salt with formula C
6H
10CaO
6, consisting of two lactate anions H
3C(CHOH)CO−
2 for each calcium cation Ca2+
. It forms several hydrates, the most common being the pentahydrate C
6H
10CaO
6·5H
2O.
Acidogenesis is the second stage in the four stages of anaerobic digestion:
Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food. This includes the study of microorganisms causing food spoilage; pathogens that may cause disease ; microbes used to produce fermented foods such as cheese, yogurt, bread, beer, and wine; and microbes with other useful roles, such as producing probiotics.
Cheese is a dairy product produced in a range of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk. During production, milk is usually acidified and either the enzymes of rennet or bacterial enzymes with similar activity are added to cause the casein to coagulate. The solid curds are then separated from the liquid whey and pressed into finished cheese. Some cheeses have aromatic molds on the rind, the outer layer, or throughout.
Lactobacillus helveticus is a lactic-acid producing, rod-shaped bacterium of the genus Lactobacillus. It is most commonly used in the production of American Swiss cheese and Emmental cheese, but is also sometimes used in making other styles of cheese, such as Cheddar, Parmesan, Romano, provolone, and mozzarella. The primary function of L. helveticus culture is to prevent bitterness and produce nutty flavors in the final cheese. In Emmental cheese production, L. helveticus is used in conjunction with a Propionibacterium culture, which is responsible for developing the holes through production of carbon dioxide gas.
There are many different types of cheese. Cheeses can be grouped or classified according to criteria such as length of fermentation, texture, methods of production, fat content, animal milk, and country or region of origin. The method most commonly and traditionally used is based on moisture content, which is then further narrowed down by fat content and curing or ripening methods. The criteria may either be used singly or in combination, with no single method being universally used.
Propionibacterium freudenreichii is a gram-positive, non-motile bacterium that plays an important role in the creation of Emmental cheese, and to some extent, Jarlsberg cheese, Leerdammer and Maasdam cheese. Its concentration in Swiss-type cheeses is higher than in any other cheese. Propionibacteria are commonly found in milk and dairy products, though they have also been extracted from soil. P. freudenreichii has a circular chromosome about 2.5 Mb long. When Emmental cheese is being produced, P. freudenreichii ferments lactate to form acetate, propionate, and carbon dioxide
(3 C3H6O3 → 2 C2H5CO2 + C2H3O2 + CO2).
Cheese ripening, alternatively cheese maturation or affinage, is a process in cheesemaking. It is responsible for the distinct flavour of cheese, and through the modification of "ripening agents", determines the features that define many different varieties of cheeses, such as taste, texture, and body. The process is "characterized by a series of complex physical, chemical and microbiological changes" that incorporates the agents of "bacteria and enzymes of the milk, lactic culture, rennet, lipases, added moulds or yeasts, and environmental contaminants". The majority of cheese is ripened, except for fresh cheese.
Swiss-type cheeses, also known as Alpine cheeses, are a group of hard or semi-hard cheeses with a distinct character, whose origins lie in the Alps of Europe, although they are now eaten and imitated in most cheesemaking parts of the world. Their distinct character arose from the requirements of cheese made in the summer on high Alpine grasslands, and then transported with the cows down to the valleys in the winter, in the historic culture of Alpine transhumance. Traditionally the cheeses were made in large rounds or "wheels" with a hard rind, and were robust enough for both keeping and transporting.
Enzyme-modified cheese (EMC) is a concentrated cheese flavour ingredient that is produced from cheese by treatment with enzymes such as proteases, lipases and esterases. An incubation period under controlled conditions is required for proper flavor development.These enzymes accelerate and intensify the ripening of cheese, which is normally done with enzymes released by an microbial culture. They may be added to during cheesemaking, after the cheese curds have been pressed, or even after the cheese has been naturally aged. EMCs were first made in the 1970s.
James Morgan Sherman was an American professor of bacteriology and dairy industry. He was the president of the American Society for Microbiology in 1937.