I am an apprentice cheese maker and have two cheese science questions.

1. When making camembert, we add penicillin candidum (or some other forms of penicillin) to the milk or spray it on the outside. My mother is allergic to penicillin but has never had a reaction to my camembert. Why?

2. U.S. regulations require that the milk in cheese be pasteurized or that the cheese be aged at least 60 days. I know pasteurization gets rid of bad bacteria, but why does aging?

First, we have to straighten out some terminology. You're confusing the drug with the mold, the bacteria with the diseases they cause, and the mold with the allergen -- the substance that triggers allergic reactions in some people. Here's the straight scoop:

Penicillin (not penicillium) is the name of the drug.

Penicillium (not penicillin) is the genus name of the mold that produces it.

Listeriosis and brucellosis are diseases caused by bacteria, not the names of the bacteria themselves. Got it?

The Drug The oft-told story of the "wonder drug" penicillin goes back to 1928, when the Scottish physician-bacteriologist Alexander Fleming took a vacation from his work at St. Mary's Hospital in London. He returned weeks later to find that some spores of the mold Penicillium notatum had drifted into his laboratory and settled on one of his cultures of the pathogenic Staphylococcus aureus bacteria.

(Fleming reportedly ran a rather sloppy lab and habitually left uncovered culture dishes out in the open.) He noticed that the bacteria refused to grow near where the mold colony was growing; he surmised that the Penicillium mold was releasing an antibacterial substance; he named the substance "penicillin" and he won a Nobel Prize in 1945. (Advice to aspiring Nobel laureates: Keep a sloppy lab and take long vacations.)

Today, penicillin is produced on a large scale by "farming" the mold spores of Penicilliumchrysogenum, a more prolific penicillin producer than P. notatum, in steel tanks, feeding them on "corn steep," a carbohydrate- and nitrogen-rich waste product of the wet-grinding of corn in making cornstarch.

It's important to note what your mother is and is not allergic to. She is allergic to the chemical penicillin itself (formula R-C9H11N2O4S, where R represents one of several atomic groupings), not the P. chrysogenum mold. The Penicillium molds used in cheese making do not generate penicillin, so they pose no problem for anyone who is allergic to the drug.

The Molds Several different Penicillium species are used in making cheese, either by injecting the mold culture into the cheese (interior mold-ripened cheese) or by coating the cheese rounds with the mold (surface-ripened cheeses). The molds contribute good flavors and impart a soft "bloom" to the cheese surfaces. Among the species most commonly used are P. camemberti for camembert; P. glaucum for gorgonzola; P. candidum for Brie, Coulommiers and several French goat cheeses and P. roqueforti for Roquefort, Danish blue and Stilton.

Molds are fungi that grow on moist, warm organic matter. As mycophiles (mushroom lovers) well know, there are good guys and bad guys among the fungi. Even some of the Penicillium species produce toxins that may make a food inedible or even dangerous. For example, the bluish-green mold that makes many over-the-hill foods look like Chia Pets is a Penicillium. But penicillin it is not. So throw away all moldy food, along with any nearby food that may have been exposed to its airborne spores. Don't run your kitchen like Fleming ran his lab.

The Bacteria Bacteria, of course, can also be good guys or bad guys. Among the common black-hat, pathogenic bacteria are Listeria monocytogenes and certain members of the genus Brucellae. The symptoms of infection by these bacteria are called listeriosis and brucellosis, respectively. Brucellosis goes by several different names -- Malta fever, Mediterranean fever, Cyprus fever, etc. -- depending on the part of the world in which the various Brucellae species cause trouble. The name undulant fever comes from the fact that the temperature of a brucellosis sufferer undulates up and down as the days go by.

Both the Listeria and the Brucellae bacteria, along with other pathogenic villains such as Escherichia coli O157:H7, Campylobacter jejuni and several species of Salmonella, can be contaminants in unsanitary dairies.

The Cheese For the past 50 years, the Food and Drug Administration has required that all cheeses sold in the United States, whether domestic or imported, meet any one of the following three conditions: 1) the milk it is made from has been pasteurized by being heated to 145 degrees F for 30 minutes or 161 degrees for 15 seconds, or 2) the cheese itself has been subjected to equivalent heating conditions, or 3) the cheese has been aged for at least 60 days at a temperature no lower than 35 degrees. Long aging at moderately warm temperatures dries out the curd to produce the harder cheeses such as Gruyere and cheddar, and bacteria cannot multiply without moisture. But soft cheeses, which are not aged as long, must be made from pasteurized milk.

During the past few years, the FDA has therefore been making noises about eliminating the 60-day aging option, that is, forbidding the distribution of any cheese, aged or not, that was made from unpasteurized or "raw" milk. (The second option, pasteurizing the finished cheese, is in most cases quite impractical.)

Vociferous objections to this trial balloon have been raised from many quarters, including European cheese makers and exporters, who use raw milk for most of their greatest products; American artisanal cheese makers; and just plain food lovers, all of whom point out that pasteurization damages flavor and that illness from Listeria contamination of cheese is very rare, anyway.

(Of the few hundred annual listeriosis deaths in the United States, it is difficult to pin down how many may have been caused by cheese, because other foods, notably hot dogs, delicatessen meats and chicken, are the major sources of Listeria contamination and many outbreaks have no identifiable source.)

So, can we still buy cheeses made from unpasteurized milk? Absolutely. They're sold quite legally in many markets. The labels will say "raw milk." Do some producers cheat by aging their raw milk cheeses for less than 60 days? We'll never know. Will the FDA ever get around to banning all unpasteurized cheese? If they do, it will be over the figurative dead bodies of thousands of cheese lovers.

Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author, most recently, of "What Einstein Told His Cook: Kitchen Science Explained" (W.W. Norton, hardcover, $25.95). He can be reached at wolke@pitt.edu.