Does Refrigeration Prevent Bacterial Growth in Food?

Open fridge full of groceries
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One of the factors in food poisoning is not only bacterial growth in food but the toxins that bacteria can produce as they grow. While thorough cooking will destroy the bacteria as long as there are not overwhelming quantities present, heat will not destroy the toxins.

The best way to avoid bacterial growth and the subsequent toxins is to follow proper handling instructions: keep meat cold, wash your hands and any surface that comes in contact with raw meat, never place cooked meat on a platter that held raw meat, and cook food to safe internal temperatures.

There is an exception to the general rule that refrigeration minimizes bacterial growth: Listeria monocytogenes, a bacteria that causes serious illness, can grow at refrigerator temperatures. Make sure you clean up spills in the fridge immediately. Thoroughly cook meat and poultry to 160 F and check it with a food thermometer. Hot dogs and deli meats are especially problematic with this bacteria, which is why the government recommends pregnant women and those in high-risk groups avoid those foods along with soft cheeses, smoked seafood, pates, and meat spreads.

Background on Bacteria

Bacteria are present in everything. It's impossible to completely avoid bacteria. Some bacteria are helpful to us and other varieties are very harmful. It's the harmful bacteria that we want to minimize in the food we eat.

Bacteria grow best at temperatures between 40 F and 140 F. They multiply very rapidly at those temperatures in ideal strata - that is, perishable foods like meat and dairy products. That's why it's so important to keep perishable foods refrigerated at temperatures below 40 F.

At refrigerator temperatures, that is, 32 F to 40 F, bacteria can still grow, but that growth is slowed dramatically. That's why you must use raw perishable food within a certain time frame, usually 2 to 3 days, even when it is properly refrigerated.

As bacteria grow, they can produce toxins that are not disabled, or rendered harmless, by heat. C. botulinum is the most notorious of these bacteria; the toxin is almost inevitably fatal. But since that bacteria grows in an anaerobic (oxygen-poor) environment, it is most associated with canned foods or foods stored in oil.

Other bacteria, like Staphylococcus aureus, produces a heat-stable toxin that is of concern. Salmonella creates illness, not through toxins, but the bacteria itself.

These toxins are not produced immediately by the bacteria but can take hours or even days to develop. Properly handling and storing meats and dairy products will minimize the risk of these toxins.

Refrigeration While Marinating Meat

As long as the meat is properly refrigerated while it is marinating, you do not need to make a separate batch of marinade to serve as the sauce. At refrigerator temperatures, it takes 12 hours for one bacteria to become two bacteria. There is little chance that enough toxins could be produced in that time frame to make someone sick.

And if the marinade is high in acidic ingredients, as most are, bacterial growth will be suppressed due to a low pH. Combine that environment with low temperatures and your marinating meats will be safe.

If the marinade contains toxins, they are already in the meat you are cooking and the heat will not disable them. If you are that concerned about toxins that bacteria produce, your best choice may be to avoid eating meat, period.

It's simply not possible to ensure that 100% of your food will be 100% safe 100% of the time. If you become very concerned about food poisoning, even if you handle food as safely and correctly as possible, you run the chance of not enjoying nourishment.

Safety Precautions

Always, always marinate meat in the refrigerator. If you want to be very safe, even if marinating for 20 to 30 minutes, put the meat in the fridge. And make sure the raw meat and marinade do not come into contact with any food that will be eaten raw, like fruits and vegetables.

And remember to boil the reserved marinade for 2 to 3 minutes before serving. Bring the marinade to a rolling boil that cannot be stirred down. And use a fresh spoon to serve the hot marinade. If you want to be very safe, simmer the marinade for 15 minutes.

High-Risk Groups

If, however, you have a person in the high-risk group in your household (children, elderly, pregnant women, those with chronic diseases), you may want to take that extra precaution and make a separate batch of marinade. Be sure to boil the marinade to bring it to a desirable serving temperature.

Given the concerns about food safety and the lack of proper inspections of food in this country, if you are in a high-risk group you may want to think about avoiding meat and dairy products altogether. A vegetarian diet can be safer, although fruits and vegetables can also be contaminated with bacteria through improper handling. Always scrub firm produce under running water with a clean brush, and rinse all produce under cool running water before eating. You can immerse melons in 170 F water for 3 minutes before slicing them to destroy bacteria.

Follow Safety Standards

You have to start from the point that all foods can cause a food-borne illness. Most people have developed an immunity to low levels of bacteria and will not become sick as long as the food only has a small amount of the bacteria.

The best course of action is to follow food safety standards, be scrupulous about keeping your kitchen clean and make decisions about food consumption that you are comfortable with.

Now that you're informed, you can make the decision that is best for you and your family.