Cheese Ripening

Freshly made cheese has essentially none of the flavor, aroma, rheological, or appearance properties of aged or ripened cheese. Rather, the metamorphosis from a bland, pale, rubbery mass of protein and fat into a flavorful, textured fusion of complex substances takes time and requires patience. Although efforts to reduce aging time and accelerate the ripening process have been somewhat successful (see below), for the most part, cheese ripening is a sequential process, with each step relying on a preceding step. In other words, a particular flavor compound may be present in a cheese only as a result of several preceding metabolic steps.

For example, methyl ketones, which contribute to the characteristic flavor of blue cheese, are synthesized by P. roqueforti from free fatty acids.Thus, methyl ketone formation depends on release of these acids from triglycerides via lipolytic enzymes produced by microorganisms or naturally present in the milk. Similarly, hydrogen sulfide, which is an important flavor note in aged Cheddar cheese (or may also be a defect; see below), is derived from sulfur-containing amino acids that form via protein and peptide hydrolysis.

Of course, not only is ripening a sequential process, but it also is subject to potential chaos and disarray, such that the cheese may ripen poorly or unexpectedly. In some cases, over-production of an otherwise desirable compound occurs, resulting in serious flavor defects. For example, hydrogen sulfide, at concentrations in the ppb range, imparts a pleasant aroma in Cheddar cheese, but when present at ppm levels, the cheese is nearly inedible. In contrast, while blue cheese may contain 90 ppm to 100 ppm of methyl ke-tones, a small amount (1 ppm to 2 ppm) is perfectly fine in Cheddar cheese. Controlling the ripening process, then, is key to successful and consistent production of aged and well-ripened cheese.

Many factors contribute to the ripening process, including live microorganisms, dead microorganisms, enzymes, and chemical and physical reactions. Manipulating and controlling these activities and reactions depends on characteristics intrinsic to the cheese, such as moisture, pH, salt, and Eh, as well as those extrinsic factors that are influenced by the cheese manufacturer. The latter include the source and handling of the milk, the temperature and humidity of the ripening room or environment, and other manipulations performed by the manufacturer. It is the collective result of these events that dictate the properties of the ripened cheese.

As noted above, cheese contains mostly water, protein, and fat as it leaves the vat and moves into the ripening coolers. Although some protein hydrolysis certainly occurs during the lactic fermentation by starter culture bacteria and by the action of milk proteases and the coagulant, as1, as2, and p-caseins are still intact. Similarly, the triglycerides in milk are also mostly unaffected by the early cheese-making steps. However, within just a few days, enzymes begin to attack these substrates and initiate the ripening process.

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