Keeping your food hot enough or cold enough to prevent bacterial growth is one of the core principles of food safety, but that's not always as easy as it sounds. If you have a pot of hot food, for example, and need to bring it to a safe refrigerator temperature for storage, the obvious solution is to place it in the refrigerator. Certain authorities discourage this, arguing that it stresses your fridge or places your other foods at risk. There's a grain of truth in this, but the reality is more nuanced.
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Time and Temperature
As with humans, bacteria function best within a specific range of temperatures. Below 40 degrees Fahrenheit, most are sluggish and barely active, while at temperatures above 140 F they struggle to survive. The "danger zone" is the range between those extremes, where they can -- and will -- reproduce freely. Minimizing the time your food spends in that temperature zone is central to maintaining food safety. Guidelines published by the U.S. Department of Agriculture emphasize refrigerating your foods within two hours at most, and within one hour if your ambient temperature is 90 F or higher.
Use Your Judgment
The argument against putting hot food in your fridge is clear and logical. The hot items raise the temperature in your fridge, causing it to work harder -- placing extra strain on its condenser and cooling system -- and potentially raising the temperature of all your other foods, putting them at risk. If you've prepared a few gallons of broth for later use, then whisking your pot straight from the stove to the fridge is genuinely problematic. A few sealed containers of leftovers, on the other hand, aren't going to raise the temperature of your fridge appreciably. Use your judgment and take full advantage of room-temperature cooling first.
Stack the Deck
Selected judiciously, even a brief cooling period at room temperature can sharply reduce the heat your refrigerator must cope with. Divide large pots of soup or stew into flat, shallow containers as quickly as possible. Heat dissipates much more quickly when you reduce the quantity of a liquid and increase its surface area. If you must cool a whole pot, place it in a sink of cold water or ice water, and stir regularly to shed heat. Speed matters even more by wrapping freezer gel packs in sandwich bags and dropping them into the pot. This cools your food more rapidly than refrigeration and helps it reach a food-safe temperature after a shorter time in the fridge.
Every time you open your fridge, you warm the door and the front of the shelves, so put your hot foods in the back corners where it's coldest. Use the smallest and shallowest containers you can, because those dissipate heat the most rapidly. Don't stack them, because when you do, you're doubling their thermal mass and that slows cooling. Proper air circulation provides a crucial boost to your fridge's performance, so try to leave plenty of space between and around your hot foods. If you know you'll be preparing a large batch of food for refrigeration, take a few minutes beforehand to clear away any outdated foods and reduce the airflow-blocking clutter in your fridge.