"Say cheese," the photographer says, and the subject can't help but smile. Indeed, both the word and the food itself are something to smile about. As an appetizer, sandwich entrée, or dessert with fruit, cheese is delicious, healthy, and generally a rather low-risk food as far as pathogens go. However, some cheeses can be a threat to pregnant women and those with weakened immune systems due to illness, old age, or medical treatment. But consumers can protect themselves if, before consuming or purchasing cheese, they pay attention to the type of cheese and the way it was processed. Soft cheeses are more likely than hard ones to carry a possibly deadly bacterium, but that doesn't mean that all soft cheeses are taboo for people in the high-risk categories.
The villain in this story is a bacterium called Listeria monocytogenes, which can cause an infection (listeriosis). Most healthy people will not be sickened or will develop only mild flu-like symptoms—such as fever, headaches, stiffness, nausea, abdominal pain, and diarrhea--after consuming food with sufficient quantities of this pathogen. However, listeria can be life-threatening to a fetus (particularly in the early stages of pregnancy or to the mother (in the later stages of the pregnancy). Thankfully, Listeria is relatively rare, affecting about 2,500 people in the U.S. annually. However, pregnant women are 20 times more likely than other healthy adults to contract it..
What kinds of cheeses are most risky to consume? Although there was a recent recall of a hard cheese containing listeria, the pathogen is much more commonly found in soft cheeses because they have more moisture and less acidity. Feta, Brie, Camembert, blue-veined cheese, and Mexican-style cheese (such as "queso blanco fresco" and queso fresco) are common examples of soft cheeses. (Note: For information on a recent recall of queso fresco cheese, click here: http://www.fda.gov/Safety/Recalls/ucm224712.htm)
Other types of soft cheeses—cream cheese, cottage cheese, processed (e.g.American) cheese--and the hard cheeses (such as cheddar and Parmesan) are considered safe because they've been pasteurized or otherwise processed in ways that inhibit bacterial growth.
So what should the consumer look for on the label to avoid listeria? If the cheese is pasteurized or sufficiently aged, it should be safe. According to food scientist Dr. Clair Hicks, cheese sold in the U.S. must be pasteurized or, if it is made with raw milk, aged for a least 60 days. Currently, recommendations are being considered to extend the food code from 60 to 90 days or more, Hicks told us. Therefore, Hicks recommends that, if the cheese is imported and not labeled pasteurized, the consumer should age it (in the refrigerator) for at least 90 days. Why 90 days? After 90-plus days of storage, the normal flora of bacteria in the cheese will overwhelm the Listeria, and their numbers will fall to the point where they cannot be detected."
"I would never recommend that a person, pregnant or otherwise, eat a fresh non-domestic, non-pasteurized soft cheese that had been aged less than 90 days. The risk is just too high," says Hicks. But here's the catch:he adds, "The 90-day aging would eliminate the consumption of many soft cheeses because they don't hold up for that many days of storage."
However, domestic cheeses made from raw milk and then aged for 6, 9, 12 months get Hicks' approval: "These can be a fantastic eating experience, and I would recommend these cheeses for anybody." It's the soft Hispanic cheeses that slip into the market and are not labeled correctly that Hicks warns consumers about.
Listeria is widely present in the environment, often originating from unclean water sources. It's not just found in cheeses but also in cured meat products, such as hot dogs and bologna, for these reasons: 1) it can grow (though slowly) in the refrigerator; 2) it tolerates the sodium nitrate used to "cure" meat; and 3) it likes a very small amount of oxygen, so it thrives in the vacuum-packaging of many cured meat products.
In addition to the warnings about unpasteurized cheeses already discussed in this article, the FDA offers the following suggestions regarding ways to prevent contracting listeriosis:
- Don't eat hot dogs or luncheon meats unless they're reheated until steaming hot (at least 165ºF).
- Don't eat pates or meat spreads.
- Don't eat smoked seafood unless it's in a cooked dish, such as a casserole. (This includes various types of smoked fish labeled nova-style, lox, kippered, smoked, or jerky.)
- Don't drink raw (unpasteurized milk or foods that contain unpasteurized milk.
- Observe use-by dates on packaged ready-to-eat foods and consume them as soon as possible.
Soft cheese should be consumed by the expiration date. Pasteurization really only has a minor impact on shelf life. However, pasteurized soft cheese probably has a longer shelf life than un-pasteurized cheese soft cheese. Soft cheeses have a lot of moisture in them, so their shelf life curve is a rather narrow bell curve. High moisture cheeses (in the 50+% range) have the shortest shelf life of any cheeses.
Hicks provided the following advice on freezing soft cheeses: "Most high-moisture cheese can be frozen, so, if you can't eat all of the soft cheese by the code date, just freeze it. As long as the cheese has a skin-tight package to prevent freezer burn, it can be frozen for more than a year. Thaw the cheese in the refrigerator for a day or so, and it will retain its flavor attributes and most of its texture attributes."
Clemson Cooperative Extension offers this warning: "Throw out soft cheeses that have been at room temperature for more than four hours."
One final piece of advice: At a party, don't eat soft cheese if you don't know whether it's been pasteurized or properly aged.
For more information about soft cheese on this site, click here: http://shelflifeadvice.com/dairy/cheese/soft-cheese
Clair Hicks, Ph.D., University of Kentucky, Dept. of Animal and Food Sciences
fda.gov Food "While You're Pregnant—Listeria"
babycenter.com "Is it safe to eat soft cheese when you're pregnant?" by Amanda Leonard, registered dietitian
USDA News and Events Podcasts "Script: Let's Talk About Listeria"
Clemson Uiversity, Clemson Cooperative Extension
"Handling of Cheese for Safety and Quality"