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Blue cheese is a general classification of cheeses that have had cultures of the mold Penicillium added so that the final product is spotted or veined throughout with blue mold that carries a distinct smell, either from that or various specially cultivated bacteria. Some blue cheeses are injected with spores before the curds form, and others have spores mixed in with the curds after they form. Blue cheeses are typically aged in a temperature-controlled environment such as a cave. Blue cheese can be eaten by itself or can be spread, crumbled or melted into or over foods.
The characteristic flavor of blue cheeses tends to be sharp and salty. The smell of this food is due to both the mold and types of bacteria encouraged to grow on the cheese: for example, the bacterium Brevibacterium linens is responsible for the smell of many blue cheeses, as well as foot odor and other human body odors.
Blue cheese is believed to have been discovered by accident when cheeses were stored in natural temperatures and moisture-controlled caves which happen to be favorable environments for many varieties of harmless mold. It was moist in the cave so the mold would form. According to legend, one of the first blue cheeses, Roquefort, was discovered when a young boy, eating bread and ewes' milk cheese, abandoned his meal in a nearby cave after seeing a beautiful girl in the distance. When he returned months later, the mold (Penicillium roqueforti) had transformed his cheese into Roquefort.
Gorgonzola is one of the oldest known blue cheeses, having been created around AD 879, though it is said that it did not actually contain blue veins until around the 11th century. Stilton is a relatively new addition becoming popular sometime in the early 1700s. Many varieties of blue cheese that originated subsequently, such as the 20th century Danablu and Cambozola, were an attempt to fill the demand for Roquefort-style cheeses that were prohibitive due to either cost or politics.
Similarly to other varieties of cheese, the process of making blue cheese consists of six standard steps, as well as further additions that give this blue-veined cheese its particular properties.
The first step is acidification where a starter culture is added to milk in order to change lactose to lactic acid, thus changing the acidity of the milk and turning it from liquid to solid. The next step is coagulation, where rennet, a mixture of rennin and other material found in the stomach lining of a calf is added to solidify the milk further. Following this, thick curds are cut typically with a knife to encourage the release of liquid or whey. The smaller the curds are cut, the thicker and harder the resulting cheese will become. Salt is then added to provide flavor as well as to act as a preservative so the cheese does not spoil. Next, the cheese is given its form and further pressed with weights if necessary to expel any excess liquid. The final step is ripening the cheese by aging it. The temperature and the level of humidity in the room where the cheese is aging is monitored to ensure the cheese does not spoil or lose its optimal flavor and texture.
Blue cheese undergoes the aforementioned steps with an added step to give it blue veins. These are a result of adding the molds Penicillium roqueforti and Penicillium glaucum to the cheesemaking process, often introduced after the curds have been ladled into containers in order to be drained and formed into a full wheel of cheese. Although Penicillium roqueforti and Penicillium glaucum are found naturally, cheese producers nowadays use commercially manufactured Penicillium roqueforti culture that have been freeze-dried, a form of dehydration where water is evaporated from the frozen state without the transition through the liquid state, to retain their value and are activated with the addition of water. After the addition of the molds to the cheese, the next significant step is needling, which is when the wheels of blue cheese are pierced to create small openings to allow the air to enter and feed the mold cultures, thus encouraging the formation of blue veins.
The distinctive flavor and aroma of blue cheese arises from methyl ketones (including 2-pentanone, 2-heptanone, and 2-nonanone) which are a metabolic product of Penicillium roqueforti. These compounds are not formed in other types of cheese fermented by bacterial acidification alone.
The main structure of the blue cheese comes from the aggregation of the casein. In milk, casein does not aggregate because of the outer layer of the particle, called the “hairy layer.” The hairy layer consists of κ-casein, which are strings of polypeptides that extend outward from the center of the casein micelle. The entanglement of the hairy layer between casein micelles decreases the entropy of the system because it constrains the micelles, preventing them from spreading out. Curds form, however, due to the function that the enzyme, rennet, plays in removing the hairy layer in the casein micelle. Rennet is an enzyme that cleaves the κ-casein off the casein micelle, thus removing the strain that occurs when the hairy layer entangles. The casein micelles are then able to aggregate together when they collide with each other, forming the curds that can then be made into blue cheese.
Penicillium roqueforti and Penicillium glaucum are both molds that require the presence of oxygen to grow. Therefore, initial fermentation of the cheese is done by lactic acid bacteria. The lactic acid bacteria, however, are killed by the low pH and the secondary fermenters, Penicillium roqueforti, take over and break the lactic acid down, maintaining a pH in the aged cheese above 6.0. As the pH rises again from the loss of lactic acid, the enzymes in the molds responsible for lipolysis and proteolysis are more active and can continue to ferment the cheese because they are optimal at a pH of 6.0.
Penicillium roqueforti creates the characteristic blue veins in blue cheese after the aged curds have been pierced, forming air tunnels in the cheese. When given oxygen, the mold is able to grow along the surface of the curd-air interface. In pressing the cheese, the curds are not tightly packed in order to allow for air gaps between them. After piercing, the mold can also grow in between the curds.
In the European Union, many blue cheeses, such as Cabrales, Danablu, Gorgonzola, Roquefort and Blue Stilton, carry a protected designation of origin, meaning they can bear the name only if they have been made in a particular region. Similarly, individual countries have protections of their own such as France's Appellation d'Origine Contrôlée and Italy's Denominazione di Origine Protetta. Blue cheeses with no protected origin name are designated simply "blue cheese".
Properties of the Three Great Blue Cheeses of the WorldEdit
Gorgonzola, Stilton, and Roquefort are considered to be the three great blue cheeses of the world. These 3 famous cheeses all have a protected designation of origin in which they may only be called their respective name if produced a certain way in a certain place of the world. In this section, we explore some of their microbiological, physical, and chemical properties which contribute to their unique colour, flavour, and aroma.
Gorgonzola blue cheese takes its name from the village of Gorgonzola in Italy where it was first made. Belonging to the family of Stracchino cheeses, Gorgonzola is a whole milk, white, and "uncooked" cheese. This blue cheese has been inoculated with Penicillium glaucum which, during ripening, produces the famous characteristic of blue-green veins. According to research, the odour of Gorgonzola varies between natural and creamy Gorgonzola cheese. 63 components in natural Gorgonzola cheese and 52 components in creamy Gorgonzola cheese contribute to odour with 2-nonanone, 1-octen-3-ol, 2-heptanol, ethyl hexanoate, methylanisole and 2-heptanone being the most important compounds to odour in both cheeses. Gorgonzola cheese is considered to be "naturally lactose-free" due to its very low content of glucose, galactose, and lactose.
Stilton blue cheese had been first produced in the village of Stilton in England. Different from Stichelton, which is made from raw milk, Stilton cheese is made from pasteurized milk. In addition to being inoculated with Penicillium roqueforti to give it the blue vein characteristic, research has shown that other microbiota which are relatives of Lactococcus lactis, Enterococcus faecalis, Lactobacillus plantarum, Lactobacillus curvatus, Leuconostoc mesenteroides, Staphylococcus equorum, and Staphylococcus sp. can also be found in Stilton cheese. Some important microbiota contribute to the aromatic profile such as those of the Lactobacillus genus due to their production of volatile compounds. During ripening, free fatty acids increase in amount which contribute to the characteristic flavour of blue cheeses due to fat breakdown by Penicillium roqueforti.
Roquefort blue cheese originates from the village of Roquefort-sur-Soulzon in France. Roquefort cheese's unique flavours come from the use of unpasteurized sheep's milk, inoculation with Penicillium roqueforti, and the special conditions of the natural caves of Roquefort-sur-Soulzon in which they are ripened. Penicillium roqueforti is the cause of the blue veins in Roquefort cheese. In addition to Penicillium roqueforti, a variety of yeasts are also present; namely Debaryomyces hansenii and its non-sporulating form Candida famata, and Kluyveromyces lactis and its non-sporulating form Candida sphaerica. Similarly to other kinds of blue cheeses, Roquefort's flavour and odour can be attributed to the particular mixture of methyl ketones such as 2-heptanone, 2-pentanone, and 2-nonanone.
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