understand all of it. The starting material is always milk to which they add either bacteria or

rennet. Rennet is a substance found in the stomachs of some unweaned animals and cheese

makers usually employ the most-commonly available calf rennet. It contains the enzyme rennin,

that coagulates milk. Shortages of rennet spurred biotechnologists to genetically engineer the

enzyme in the laboratory using bacterial fermentation. The U. S. Food and Drug Administration

approved the use of genetically engineered rennet in 1990, and it has been in use ever since.

Today about 60 percent of all our cheeses are produced by genetically engineered rennet.

Whether by bacteria or rennet, lactic acid forms from lactose (milk sugar), as the heated

milk coagulates. As a result, clumps of soft, jelly-like curds appear. Bacteria produce curds in

anywhere from 5 to 16 hours, while rennet produces curds within 15 to 30 minutes. Obviously,

the cheese industry prefers the considerably faster rennet. The liquid left over after the curds

form is the whey.

Many vegetarians refuse to eat cheese made with rennet because it is an animal-derived

product, referring to the fact that the animal had to die to provide the rennet. Their stand is

uncertain at this point because genetically-engineered rennet is so widely used in cheese making.

But health-food stores regularly sell more costly rennet-free cheeses, that had bacterial

coagulation.

TASTINGS The discovery of rennet

Curdling by rennet must have been discovered in ancient times, probably by the

Central Asian nomads who survived mostly on a dairy diet. They carried their

fresh milk in leather pouches made from animal stomachs. Someone one day must

have used the stomach of an unweaned calf. What a surprise they must have had

the first time they opened their pouch for a refreshing drink, only to find that it

had turned into solid chunks floating in whey (that didn’t taste too bad).

Here is a brief synopsis of how cheese-makers produce cheese once they have the curds:

1.First they gently cut the curds with huge sets of knives or steel wires to increase the

surface area. This speeds up the expulsion of the whey. Then they slowly cook the curds at low

heat to drive out even more whey. Heating of the soft, semisolid mass also gives it an incipient

texture, reduces moisture and kills harmful bacteria.

2. Next they drain off as much whey as possible through strainers, and they place the

curds into containers that form the final huge cheese blocks shapes. They leave these to rest or,

as they call it, to knit. This allows the lactic acid to develop the characteristic texture of the

particular cheese and helps to further reduce moisture.

3. After resting they sprinkle salt over the surface of the cheese blocks. This further helps

to develop texture, improves the appearance and draws out even more moisture. Salt also checks

lactic acid fermentation, suppresses the activity of harmful microorganisms and contributes to

the final flavor.

4. But they still have to get rid of more moisture. They press the cheese blocks by heavy

weights or by mechanical pressure between 6 and 18 hours, which drains more trapped whey.

How much pressure they apply and for how long varies from one kind of cheese to another. At

this point, they still only have solid blocks of salty, faintly milk-tasting flavorless cheese.

5. The last important step, ripening (also called aging), is what really develops the true

flavor of the cheese. Ripening progresses simultaneously on two levels. Live bacteria work on

one level and enzymes on the second. They both produce different flavor chemicals, and those

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