Cheese ripening the cheese by fungi to occur. Mould-ripened cheeses ripen faster than hard cheeses, in weeks as opposed to the typical months or even years. This is because the fungi used are more biochemically active than the starter bacteria. Where the ripening occurs is largely dependent on the type of cheese: some cheeses are surface-ripened by moulds, such as Camembert and Brie; and some are ripened internally, such as Stilton. Surface ripening of some cheeses, such as Saint-Nectaire cheese, may also be influenced by yeasts which contribute flavour and coat texture. Others are allowed by the cheesemaker to develop bacterial surface
Cheeses of Mexico aged cheeses held for weeks or months, are aged for only days. This is not enough time to change the pH of the cheese enough to kill any harmful bacteria that may have been in the (unpasteurized) milk at the beginning of the process. The use of raw milk has led to a number of instances of food-borne disease linked to cheese, especially unaged, “fresh” cheeses. Cases of tuberculosis, listeriosis, and other diseases linked to cheese made in Mexico have led to strong restrictions against bringing the same across the US border or along with air travelers entering US airports.