Refrigerating hot food: any scientific rationales?
I've always put cooked food, be it meat, pizza, soup, stew, roasts, you name it -- into the refrigerator while still hot. Not fresh off the boil, mind you, but at least a half-hour off the heat source.
I realize that this will heat up food next to it, but the problems with that seem to be to me negligible.
Yet some insist that you should wait until the food has completely cooled down to room temperature before they refrigerate/freeze it. I see no scientific explanation as to why this should be so. I figure, the faster something cools down, the better, as room temp is right about the region in which the bad bugs really thrive.
Any arguments, pro or con? (I once had a girlfriend who always left food out overnight -- uncovered. It was completely gross, and when she suggested that we have that again for dinner, well, you can see why she's an ex.)
I think Hounds have chimed in with a lot of good info from a lot of good sources here. Of course, the most conservative approach is the best approach when safety is a concern, but something else one might consider in regards to bugaboos and food safety.
I can't obviously speak for everyone, but in our household, heating up/cooking foods usually means heating it to a temp that is considered high enough to severely degrade/kill off that 99.9% of bacteria. We live in SoCal, where the air is on the drier side, and temps tend to be mild. Cooling off food to a reasonable temp to then put into the fridge takes anywhere from 30 minutes to 1 1/2 hours. The span of time (IMHO) is short enough not to let the worries of bacteria to reform/reestablish themselves. On top of that, if one has brought the considered dish up to a temp prior to serving where the food is relatively sterile, the starting point for bacteria infiltration is nil to very low. I don't ever recall having food poisoning in our household to where we could objectively point at something we had cooked, cooled off and stored, then reheated.
I think if you live in a humid environment, where ambient temps are high, and/or air circulation is via ducts that are poorly maintained, or a swamp cooler is involved, the chances of bugaboo spawn and growth are much higher. Anything where food has been unevenly heated obviously can pose risks as well. I guess the bottom line for me is, one has to take a lot of factors into consideration along with general safety guidelines.
PS: Another obvious mention is relative cleanliness in the areas where food is prepared, cooked, served and stored; e.g., multiple kids, pets in/on any of these areas, frequency and effectiveness of cleaning/sanitizing regimens can challenge even the best of otherwise good intentions.
One not-so-scientific reason to put food in the fridge before it is completely cool is to avoid forgetting to put whatever it in to the fridge later. My dad is particularly bad at this. My mum will come downstairs in the morning to find whatever leftovers she had planned for lunch congealing nicely in the side.
There is also an energy rationale too... as Cowboy pointed out, your food isn't going to cool that much faster in the fridge versus the counter, but your fridge is going to work hard keeping the temperature inside below 40*. Depending on the mass of the foodstuff you're cooling, to a certain degree, cooling it on the counter is more energy efficient and not at all harmful to your health.
I see the faster-the-better theories prevail. Good, that's what i've always done. But a lucky bunch of us may not realise the most efficient way of getting food temperature down quickly: when it's below zero (C, 32F) outdoors , I just drag whatever it is out onto the balcony table. And If I know it's going to be cold for a while, I just leave it there (mainly large containers of soup or such. Sometimes I have quite a party going on on the balcony! I would surmise that even if the temp were, say, only 10 or so (50F) it still would be a quick way to get the temperature down for the fridge.
I think you're being a bit over-zealous. There was an article about this in the NYT by Harold McGee a fews weeks ago. I've pasted what I think is the most relevant quote from the food specialist consulted for the story -
Dr. Snyder agreed that official pronouncements on food safety can be inconsistent and self-defeating. “The F.D.A. Food Code is very conservatively written,” he wrote. “Four hours after it’s cooked is plenty fast enough to get food into the refrigerator.” And slow enough to relax and enjoy the meal.
Dr. Snyder added that it’s safest to cool leftovers uncovered and in a mass no thicker than two inches, so they cool through quickly. If they’re still hot, start the cooling on the countertop. When the container is no longer hot to the touch, put it in the refrigerator, and cover it once the food is good and cold. "
Here's the link to the story
The way I've always learned is (from the CIA: Professional Chef)
"One of the leading causes of food-borne illness is improperly cooled food. Cooked foods that are to be stored need to be cooled to below 41°F/5°C as quickly as possible. This should be completed within four hours, unless you use the two-stage cooling method. In the first stage of this method, foods must be cooled to 70°F/21°C within two hours. In the second stage, foods must reach 41°F/5°C or below within an additional four hours, for a total cooling time of six hours.
The proper way to cool hot liquids is to place them in a metal container in an ice water bath that reaches the same level as the liquid inside the container. Stir the liquid in the container frequently so that the warmer liquid at the center mixes with the cooler liquid at the outside edges of the container, bringing the overall temperature down more rapidly.
Semisolid and solid foods should be refrigerated in single layers in shallow containers to allow greater surface exposure to the cold air. For the same reason, large cuts of meat or other foods should be cut into smaller portions, cooled to room temperature, and wrapped before refrigerating."
I think the only big factor to worry about is whether the food will heat your refrigerator or nearby foods to unsafe levels. So in other words, putting a hot turkey wing in the fridge is no problem. Putting a whole hot turkey into the fridge - problem.
The other thing to keep in mind - hot food doesn't cool THAT much more quickly in refrigerator temps than it does at room temp (at least when air is the cooling medium). It's only a ~35 degree difference in air temp. Same principle as why a hunk of meat doesn't cook that much faster at 435 than it does at 400. So there's not necessarily that much to be gained by cooling a big hunk/tray of whatever in the fridge rather than cooling it to near room temp outside the fridge and then putting it in the fridge.
You're right. You've got two competing factors here -- the need to get the hot food cooled down as quickly as possible, and the need to avoid heating up a refrigerator full of food, which would likely happen if, say, you put an enormous pot of boiling stock in the fridge.
So most of the time recipes tell you to let something cool at room temp for a little while before refrigerating. But certainly not overnight. They generally say you can leave something out for about two hours, no more.
I cool pots of stock in ice. I can get them down to room temp in a half-hour or less, then into the fridge.