Should Hot Food Go into the Fridge?

Cooking a holiday dinner for a crowd?  Then chances are, you're planning to prepare some hot dishes a day or two in advance.  Then, you may ask yourself, can my casserole go right from the oven into the fridge, or is that a bad idea?  This quandary actually poses 3 questions:

1) Will hot food damage my refrigerator?

2) Will adding hot food harm my already refrigerated food?

3) Will immediate refrigeration be bad for the hot food?  We asked two members of our Advisory Board, Dr. Timothy Bowser, a food process engineer, and Dr. Karin Allen, a food scientist, to provide the answers.

1) Will hot food damage my refrigerator?

Dr. Bowser: From an engineer's standpoint, it's pretty hard to damage a refrigerator by putting hot food in it (unless it melts the plastic shelves). However, uncovered food with a lot of moisture in it could evaporate large quantities of water which could ice over an air vent, coil, or door.

Dr. Allen: Hot food puts a strain on your fridge.  The efficiency of a fridge relies on constant and even air flow, so always make sure it's not tightly packed.  (Note: this isn't true of the freezer).   If you must put hot food in, divide it into smaller containers, put them into different areas of the fridge, and leave a lot of air space around them.

2) Will adding hot food harm my already refrigerated food?

Dr. Allen: Hot food can cause the neighboring items to warm up into the "danger zone" (40ºF - 140ºF), allowing bacterial growth in those foods.

Dr. Bowser: How much hot food you could place in a refrigerator depends upon the capacity and design of your refrigerator, the thermal conductivity of the food and container, the thickness of the food, and other factors that affect the cooling rate. Food should be cooled down to at least 130-140ºF before being placed in the refrigerator.

3) Will immediate refrigeration be bad for the hot food itself?

Probably not, but considering that it's not good for the efficiency of the fridge or the bacterial content of nearby perishables, don't do it.  Also, if a large amount of hot food is refrigerated (such as a large pot of chili or a casserole) without being put into two or more smaller containers, the food in the center may not cool fast enough to avoid becoming contaminated with bacteria. Food does not cool evenly; the parts closer to the surface and to the metal sides cool more quickly.  Therefore, it's also not a good idea to let foods cool slowly on the stove or counter.  The parts that cool more rapidly could enter the "danger zone" and become contaminated.

The general rule about perishables is that they should never be left at room temperature for more than 2 hours, and the usual advice is to get them back into the fridge as soon as possible. To accomplish this, use one or more of these rapid cooling methods:

Dr. Bowser: It's a good idea to cool down hot foods before refrigerating them by techniques such as these: shallow pans, thin portions, an ice water bath, metal containers (which facilitate heat transfer), and/or ice as an ingredient.

Dr. Allen:

1) The best way by far to cool foods is with a cooling bath [by placing the container of hot food into a pan holding water and ice].  As long as pieces of ice are visible, the water temperature is exactly 32ºF.  Use more water than ice to start; then add extra ice only as needed.

2) Clean metal bowls can be pre-chilled in the freezer and then used to cool the food more rapidly.

3) Freezer packs (or the freezable sticks that come in beverage containers) can be put into the food to cool it.  Just make sure that the freezer packs are food safe, or that they are tightly sealed in a Ziploc bag first. Actually,  I recommend plastic bags around all freezer sticks you've used before to  avoid having chili-flavored water the next time you use the sticks.

4) Stir the food constantly. This will help cool it down more evenly and quickly.

[Editor's note: To summarize the answer to our title question: no, hot food shouldn't be refrigerated.  But once it's cooled down to 140ºF or so, it's ready to join your other perishables in the fridge.]

Source(s):

Timothy J. Bowser, Ph.D.  Oklahoma State University, Dept. of Biosystems and Agricultural Engineering

Karin E. Allen, Ph.D., Utah State University, Dept. of Nutrition, Dietetics, and Food Sciences

Link(s):

thekitchen.com  "Food Safety: How to Use Ice Baths to Cool Food Quickly"
http://www.thekitchn.com/thekitchn/tips-techniques/food-safety-how-to-use-ice-baths-to-cool-food-quickly-048957