A “cheesy” beginning

What is the common theme here: Reggianito, Etzy Ketzy, Catupiry, Kanafeh, Blu Della Casera, Brunost, and Chhurpi? Intriguing names? Yes. Types of cheese? Bingo.

Cheese is obtained by converting milk into a solid or semi-solid state, by a process known as coagulation. This process breaks down the milk protein, casein, causing it to clump together and form cheese. Coagulation can be carried out by two methods: 1. By adding an acid, such as lime juice or 2. By using rennet which is a cocktail of enzymes found in the stomach of ruminant animals, such as cows. Both these processes cause casein to lose its structure and form aggregates, which results in the formation of curd. To make cheese, the curd is heated, pressed to remove excess moisture, salted, and then ripened. The ripening process is sometimes aided by the addition of micro-organisms.

The origins of cheese making date back to the Neolithic period between 5400-4800 BC. The study conducted by Salque et al., in 2012, describes the earliest evidence of cheese production, through the discovery of milk fat in several pottery vessels resembling sieves or cheese strainers. The making of cheese seems to be accidental; nomadic tribes used to carry milk in bags made from the lining of animal stomachs. This practice, coupled with the churning that occurred due to galloping motion of the horse, would likely have caused the curdling of milk, which could then be sieved to make cheese.

It remains unclear at what point the deliberate addition of microbes to the cheese making process occurred. However, the role of microbiology and cheese making is inextricably linked. In large scale manufacturing of cheeses, it is common to use starter cultures of lactic acid bacteria (LAB). These bacteria (usually belonging to Lactobacillus, Lactococcus, and Streptococcus families) are capable of breaking down the milk sugars to form lactic acid. This process is then coupled with the addition of rennet to maximize the coagulation of milk proteins. The starter cultures also contribute to the flavor of aged cheese and prevent the growth of pathogens as well as undesirable organisms, which result in spoilage.

Figure 2: Lactobacillus acidophilus– one of the LAB species that is used as a starter culture. It is commonly used in yogurt. Source.

In addition to starter cultures, adjunct cultures are used to provide additional flavors and textures to cheese. These organisms can be bacteria, yeast, and mold. Some of them are listed below.

• Lactobacillus casei and Lactobacillus plantarum are used as secondary cultures in Cheddar cheese. These bacteria contribute to the flavor and texture by breaking down the proteins, fats, and sugars in milk to release volatile compounds. Fun fact: These bacteria do not contribute to the typical orange color of Cheddar; that color comes from the flavorless Annatto seed that is added to dye the cheese.

Figure 3: Annatto seeds. These seeds are also used as coloring agents for Gloucester cheese, Chesire, Red Leicester, and processed cheese products such as American cheese. Source.

•  Propionibacterium freudenreichii is used to create “eyes” in Swiss cheese. During the cheese production, this bacterium uses the generated lactic acid to produce carbon dioxide, acetate, and propionic acid. The carbon dioxide forms bubbles that riddles the cheese with holes. Acetate and propionic acid give Swiss cheese its distinctive nutty flavor. Interestingly, a relative of this bacterium, Propionibacterium acnes, is the principle cause of acne.
• Brevibacterium linens, which is also responsible for foot odor, is used to smear cheeses such as Limburger and Münster (Now you know why some smelly feet remind you of cheese!). Such surface-ripened cheeses (which ripen from the rind to the inward paste) have a complex and transient microflora; they are initially dominated by yeast and then by bacteria such as Brevibacterium. The yeast breaks down the lactate present in curd, raising the pH, which allows bacteria to grow. The growth of the bacteria is also facilitated by brine-washing the cheese surface. The bacteria produce pungent odors by releasing sulfur compounds and contribute to the firm rind around the cheese.

Figure 4: Limburger cheese with the outer rind. Source.

Fun fact: In 2006, a study showed that the malaria mosquito is attracted equally to the smell of Limburger and the smell of human feet. Cheese eaters beware!

• Penicillium camemberti and Penicillium roqueforti are used to make Camembert and blue cheese respectively. P. camemberti forms a distinctive hard, white crust and can be either mixed initially with the other ingredients or added to the cheese afterward. Blue cheese is characterized by the spotted blue color of the P. roqueforti cultures. Blue cheese was believed to have been discovered by accident when cheeses were stored in caves; the moist and temperature-controlled environments were ideal for fungal growth. An interesting legend claims that Roquefort was discovered when a youth, distracted by a beautiful girl, left his meal of ewe’s milk cheese in a cave and returned several months later to discover that his cheese had turned into Roquefort.

Figure 5: Stilton, a blue cheese from England. When the cheese is still in its curd form, it is inoculated with Penicillium roqueforti. Subsequently, the fungi grow within the cheese as it ages imparting the characteristic appearance and taste. Source.

There are around 900 known types of cheeses in the world. The exact number varies based on how one categorizes them: moisture content, the source of milk, types of starter cultures and adjunct cultures, and processing techniques. This article highlights the most common techniques and cultures employed to make cheese. Understanding the science behind cheese-making will hopefully make the eating experience more enjoyable for you. Bon appetit!

Author

Ananya Sen is currently a Ph.D. student in Microbiology at the University of Illinois at Urbana-Champaign. When she’s not studying oxidative stress, she is busy pursuing her passion for scientific writing. Currently, she contributes articles to ASM,  ScienceSeeker, and her own blog where she discusses the history of various scientific processes. She is an ardent reader and will happily discuss anything from Jane Austen to Gillian Flynn. Her graduation goals include covering all the national parks in the U.S. with her sidekick Oscar, a Schnauzer/Pomeranian mix.

Editor

Roopsha Sengupta did her Ph.D. at the Institute of Molecular Pathology, Vienna and postdoctoral research at the Gurdon Institute, University of Cambridge, UK, specializing in the field of Epigenetics. During her research, she was involved in many exciting discoveries and had the privilege of working and collaborating with a number of inspiring scientists. As an editor for ClubSciWri, she loves working on a wide range of topics and presenting articles coherently, while nudging authors to give their best.

Blog Design: Roopsha Sengupta

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This article was first published in Ananya’s blog. This is an edited version.

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