Who Discovered Penicillin, How is Penicillium used to Make Cheese, and Why is Cheese Aged?

First, we have to straighten out some terminology:

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

• Penicillium (not penicillin) is the genus of the mold that produces the drug.

• Listeriosis and brucellosis are diseases caused by bacteria, not the names of the bacteria themselves.

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, and surmised that the Penicillium mold was releasing some kind of antibacterial substance. He named the substance “penicillin” and won a Nobel Prize for it 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 Penicillium chrysogenum, 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 understand what people are and are not allergic to. Some people are allergic to the chemical penicillin itself, 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. 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 dangerous. For example, the bluish-green mold that makes your 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.

Several different Penicillium species are used in making cheese, either by injecting the mold culture into the cheese (interior-ripened cheese) or by coating the cheese rounds with the mold (surfaceripened cheese). 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; candidum for Brie, Coulommiers, and several French goat cheeses, and P. roqueforti for Roquefort, Danish blue, and Stilton.

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 Brucella. 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 B rucella species have caused the most trouble. (The name undulant fever comes from the fact that the fever chart of a brucellosis sufferer undulates up and down as the days go by.)

Both the Listeria and the Brucella bacteria, along with other pathogenic villains such as Campylobacterjejuni, several species of Salmonella, and the ever-popular Escherichia coli 0157:H7 can breed in the moist environments of dairies and cheese plants.

The cheese. For more than fifty-five years, the FDA 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°F (63°C) for 30 minutes or 161°F (72°C) for 15 seconds, (2) the cheese itself has been subjected to equivalent heating conditions, or (3) the cheese has been aged for at least sixty days at a temperature no lower than 35°F (1.7°C). Long aging to produce the harder cheeses such as Gruyere and Cheddar both increases the acidity of the curd and dries it out, and many bacteria cannot multiply under dry, acidic conditions. But soft cheeses, which are not aged as long, cannot be made with absolute safety from unpasteurized milk.

Over the past several years, the FDA has been making noises about lengthening or eliminating the sixty-day aging option, that is, forbidding the distribution of any cheese, aged or not, that was made from unpasteurized or “raw” milk, on the grounds that Listeria and E. coli bacteria have been known to survive a sixty-day aging period.

(The second option, pasteurizing the finished cheese, is in most cases quite impractical.)

Vociferous objections to this trial balloon have been raised in many quarters, including European cheese makers and exporters, who use raw milk for many of the products they’re most proud of; American artisanal cheese makers; and just plain food lovers, many of whom believe 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? Yes. As of this writing, they’re sold quite legally in many markets. The labels will say they’re made from “raw milk.” Do some producers cheat by aging their raw-milk cheeses for less than sixty days? Indubitably. Will the FDA ever ban all unpasteurized cheese? If they do, it will be over the figurative dead bodies of thousands of cheese lovers.

Tune in tomorrow for the next episode of “As the Cheese Wheel Turns.”