Although cheeses like cottage cheese and quarg are consumed fresh, most cheeses require a ripening period (from a few weeks up to several years) for development of characteristic flavor, consistency, and appearance. The changes during ripening are brought about by enzymes and microorganisms. The effects of the enzymes and the microorganisms depend on pH and temperature, on the content of moisture and of salt, and on the surface treatment. Examples of regimens for storage for ripening:
Emmental: 2 weeks at 12°C; 3-6 weeks at 20-24°C; then at 8-10°C Cheddar: 4-12 months at 6-10°C
Semihard cheeses: Gouda/Danbo, etc.: 2-4 weeks at 12-18°C; then at 6-10°C
Blue-veined cheese: 3-5 weeks at 8-12°C; 1-3 months at 2-6°C
White mold cheese: 1-2 weeks at 12-15°C; 1-2 weeks at 6-10°C; 2-6 weeks at 2-5°C
The fermentation of lactose to lactic acid by lactic acid bacteria, and the fermentation of citrate by citrate using bacteria in DL-starters, is described in the sections above. In cheeses such as Emmental and other large-eyed cheeses, lactic acid is further fermented by propionic acid bacteria to propionic acid, acetic acid, and CO2.
The caseins are gradually hydrolyzed by rennet proteinase enzymes and by plasmin, an indigenous milk protease, which yields a number of large polypeptides; the latter do not influence the flavor of the cheese, but some hydrophobic peptides may be astringent or may have a bitter taste. These first steps of the proteolysis are important for changing the structure of semihard cheeses from a rubberlike to a sliceable consistency.
Some of the peptide bonds in the polypeptides can be further hydrolyzed by enzymes from the lactic acid bacteria to yield smaller peptides and free amino acids, contributing to the basic taste of cheese. Amino acids may be further converted to smaller molecules— ammonia, organic acids, amines, esters, low molecular sulfur compounds, etc.—contribu-ting to the aroma of ripened cheese.
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