The origin of cheese is lost in antiquity. But, most assuredly, milk was contaminated with lactic acid bacteria, which through acidification of the milk, created conditions unfavorable for growth of other bacteria. As the story goes, milk held in storage vessels (animal stomachs) clotted, making cream cheese, the ''mother of all cheeses.'' The acid environment caused milk proteins to clot. It was a great leap forward when centuries later humans discovered the use of coagulating enzymes. This led to production of less sour cheeses. Natural contamination of milk or cheese by bacteria, yeasts, and molds led to development of a multitude of flavor sensations in cheese as it aged. Imagine, a long time ago, when humans first tasted that odorous morsel covered with colorful molds, yeasts, and bacteria. But now consider a world without Roquefort, Stilton, Limburger, or Gruyere. Boring! Unthinkable!

Modern cheese making is controlled and has been refined through strict adherence to manufacturing guidelines and careful selection of specific lactic acid bacteria and ripening microorganisms. Even so, sometimes there are problems. No cheese is produced in a sterile environment, so contamination is inevitable. One of the chief causes of poor flavor quality in cheese is the undesirable metabolism of contaminating microorganisms. A preventable cause of poor-quality flavor is that many retailers sell products long after they have reached the end of their expected shelf life. The ability of a cheese to age well with regard to undesirable microbial growth depends on cheese composition, manufacturing protocol, level of contamination, and ability of the contaminants to grow in cheese. There fore, cheese maker, retailer, and consumer must be aware of limitations of the product with regard to growth of contaminants and defects that they cause. It must be kept in mind that not all undesirable attributes of a cheese result from contaminating microorganisms. Some cheese defects may be caused by poor milk quality (late lactation milk, milk from mastitic animals high in enzymes of animal origin, i.e. lipase and protease), inappropriate rate of acid development by the starter, or poor manufacturing and storage regimens.

Although there are more than 1000 named varieties of cheeses worldwide, this chapter discusses only the major types.

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