Science explains how artisanal Cotija cheese develops
Artisanal Cotija is produced in the Sierra de Jalmich, an area spanning parts of Michoacán and Jalisco. Its preparation uses raw cow’s milk and methods passed between generations. Maricarmen Quirasco Baruch, an academic at the National Autonomous University of Mexico’s Faculty of Chemistry, has described the chemical, biochemical and microbiological processes involved in the cheese’s production and maturation.
The milk comes from cattle raised on open pasture, including criollo animals and crosses involving zebu and other breeds. The animals’ diet can alter the composition of the milk and some characteristics of the finished cheese. Raw milk also brings a microbial community into the process. Salt from the Cuyutlán lagoon in Colima is another defined ingredient: besides seasoning the cheese, it assists whey removal and changes the conditions in which microorganisms can develop.
After milking, the milk is taken to the production site and mixed with animal rennet. The rennet contains chymosin, an enzyme that acts on kappa-casein. This reaction causes the caseins to join into a network that holds fat and part of the water, producing the curd. The curd is then cut and left to stand so that whey can separate. The liquid contains mainly water, lactose, whey proteins, minerals and other dissolved substances.
Part of the whey is removed before the curd is placed in cloth, handled and salted by hand. Salt affects moisture and the availability of water, allowing some microorganisms to persist while restricting others. The curd is then moulded and pressed; in traditional production, stones may be used as weights. After removal from the mould, the cheese is wrapped or secured and aired before maturation begins.
The cheese examined in the account matures for no less than three months. During that period it loses moisture, while its colour, texture, aroma and taste change. Microorganisms consume lactose and produce lactic acid and other compounds. Lipids can release fatty acids, while caseins break down into peptides and amino acids. These substances may later form additional compounds involved in the cheese’s sensory profile. Quirasco Baruch compares the result with a “complex perfume”, because its flavour does not come from one molecule but from many substances in varying proportions.
Genetic analysis by UNAM researchers found three dominant microbial genera and more than 500 non-dominant genera of bacteria and archaea in the samples studied. The predominant species included Leuconostoc mesenteroides, Weissella paramesenteroides and Lactiplantibacillus plantarum, which can contribute to fermentation and the development of aroma and taste. Microorganisms may originate in the milk, salt, equipment and surrounding environment. As maturation advances, humidity falls, salt is redistributed, acidity changes and nutrient availability varies, causing some populations to increase and others to decline. The study did not establish that every Cotija wheel contains identical microorganisms in the same proportions. The account also notes that hygiene, production methods and maturation conditions remain important because not every microorganism in an artisanal product is beneficial or harmless.
