Cheese making transforms simple milk into a diverse range of products, a process practiced for thousands of years. This transformation relies heavily on the activity of various microorganisms. These tiny life forms are fundamental to converting liquid milk into solid cheese, developing the unique textures, aromas, and flavors that define different cheese varieties.
Essential Functions of Microorganisms
Microorganisms perform fundamental functions indispensable for cheese production. Their primary role involves acid production, particularly through lactic acid fermentation. Lactic acid bacteria (LAB) convert lactose, the sugar in milk, into lactic acid, which lowers the milk’s pH. This acidification causes milk proteins, specifically casein, to coagulate, forming a gel-like curd, which is the solid foundation of cheese.
Beyond curd formation, microorganisms initiate complex ripening processes. They contribute enzymes that break down proteins and fats within the curd. This enzymatic activity is responsible for developing the distinct flavors, aromas, and textures that distinguish one cheese from another.
Primary Microbes in Cheese Production
The main categories of microorganisms used in cheesemaking include bacteria, molds, and yeasts. Lactic acid bacteria (LAB) are common starter cultures, including Lactococcus, Lactobacillus, and Streptococcus. These bacteria are important for the initial acidification of milk by converting lactose into lactic acid.
Other bacteria contribute to specific cheese types. Propionibacterium freudenreichii creates the characteristic holes, or “eyes,” in Swiss cheese varieties like Emmental by producing carbon dioxide gas. Brevibacterium linens develops on the surface of washed-rind cheeses, contributing to their reddish-orange color and pungent aroma.
Molds, typically Penicillium species, are used in many ripened cheeses. Penicillium roqueforti creates the blue-green veins in blue cheeses like Roquefort and Stilton. Penicillium camemberti forms the white, velvety rind on soft cheeses such as Brie and Camembert. Yeasts, including Debaryomyces hansenii and Geotrichum candidum, also play a role in surface-ripened cheeses by deacidifying the cheese surface and influencing flavor and rind development.
Microbial Impact on Cheese Characteristics
Microbial activity shapes cheese characteristics, influencing flavor, texture, and appearance. During ripening, bacterial enzymes break down milk proteins (proteolysis) and fats (lipolysis). These processes release smaller compounds like peptides, amino acids, and fatty acids, responsible for the complex and varied flavors and aromas found in cheese. Lactic acid bacteria contribute to the initial tangy flavor through lactic acid production.
Specific microbes contribute to distinct cheese features. Propionibacterium freudenreichii consumes lactic acid, producing propionic acid, acetic acid, and carbon dioxide. The acids provide the sweet, nutty flavor of Swiss cheese, while carbon dioxide creates the large, round holes. The longer Swiss cheese ages, the larger these “eyes” can become.
Molds like Penicillium roqueforti in blue cheeses grow in low-oxygen environments, producing enzymes that break down fats and proteins. This leads to sharp, pungent flavors and characteristic blue-green veins. Penicillium camemberti on soft cheeses forms a white rind and releases enzymes that diffuse inward. These enzymes soften the interior, creating a creamy texture and contributing earthy or mushroom-like flavors.
Brevibacterium linens on washed-rind cheeses contributes to their orange color and strong, savory aromas, often described as “footy” or “barnyard-like,” due to the production of sulfur-containing compounds. Yeasts, particularly in surface-ripened varieties, consume lactic acid, raising the cheese surface pH. This creates favorable conditions for other bacteria and impacts rind formation and flavor development.
Managing Microbial Processes for Quality
Controlling microbial activity ensures consistent quality and safety in cheese production. Cheesemakers introduce specific, beneficial microorganisms, known as starter cultures, into the milk. These cultures are selected strains that perform desired functions, such as rapid acidification, and outcompete undesirable bacteria. This deliberate inoculation helps guide the fermentation process from its earliest stages.
Environmental control during ripening is another management aspect. Factors like temperature, humidity, and airflow are regulated to create optimal conditions for beneficial microbes and their enzymatic activities, while inhibiting spoilage organisms. For example, blue cheeses are often pierced to allow oxygen access, necessary for Penicillium roqueforti to thrive.
Strict hygiene and sanitation practices throughout the cheesemaking facility prevent contamination from unwanted microbes. This includes cleaning equipment and controlling air quality. By meticulously managing these microbial processes, cheesemakers can consistently produce a wide range of cheeses with predictable flavors, textures, and appearances, while also ensuring the product’s safety.