Is it ok to put still-warm food in the fridge or freezer?
January 25, 2006 2:44 AM   Subscribe

Is it ok to put still-warm leftovers in the fridge or freezer?

My girlfriend and I constantly disagree about this. She was always told, growing up, that you have to wait until recently-cooked food has cooled to room temperature before you can put it in the fridge. If you don't, she says, bacteria will grow on it much more easily and you will get sick.

I've ALWAYS just put the warm leftovers right into the fridge/freezer, and never had any problems with it, and in fact I find that the "leaving it till it cools down" often leads to food forgotten on the counter overnight, which in my opinion would be more likely to lead to spoilage. (Sweet mother of god that was a horrible runon sentence!)

My google-fu has led to little in the way of answers, does anybody have any concrete facts one way or the other? As far as I'm concerned, it just seems like common sense that bacteria is less likely (or at worst, just as likely) to grow on warm-food-in-the-cold-fridge as it is in warm-food-on-the-kitchen-counter. My girlfriend refuses to believe me, as it was SO ingrained into her brain in a child.

Help me, AskMe, you're my only hope!
posted by antifuse to Food & Drink (44 answers total) 4 users marked this as a favorite
Response by poster: Note: I haven't checked with any of her friends if they do the same thing, but I wonder if this is an Irish thing? I don't know ANYBODY at home in Canada that does this...
posted by antifuse at 2:54 AM on January 25, 2006

Best answer: The food will cool faster in the refrigerator, leading to less bacterial growth. The downside is that you'll waste a little bit of energy cooling warm food.
posted by insomnus at 3:00 AM on January 25, 2006

Best answer: I'm sure this came up in the past couple of months. Maybe one of these?

My take: most bacteria thrive between 5deg and 60deg. The faster you get out of that range, the less bacteria. Whether putting warm food in the fridge speeds the cooling process or warms other food in the fridge... not a clue. I bet it uses more energy, though.
posted by Leon at 3:04 AM on January 25, 2006

An Irish thing? I've heard that some Irish families have been cooking the same Irish stew for generations by just topping it up. I don't have any evidence but I'm with you in terms of not getting sick when whacking it straight in the freezer or fridge although I suspect it messes with the fridge dynamics.
posted by tellurian at 3:07 AM on January 25, 2006

Response by poster: Yeah, I'm not all that concerned with fridge dynamics... but maybe her parents were just thrifty with the ol' electric bill, and used a harmless little white lie to keep the kids from messing with the fridge?

And Leon: I *did* do a similar search beforehand, but none of those results really addressed my particular question.
posted by antifuse at 3:14 AM on January 25, 2006

I think the reason you wouldn't put still hot food in the freezer/fridge is that you give it time to stop "steaming" meaning you don't get condense on the inside of the plastic box. But if you don't care about a bit of water there's no reason not to do it.
posted by Skyanth at 3:16 AM on January 25, 2006

Best answer: No It is NOT an Irish thing. Yes we leave a stew on the cooker for a day or two (or rather did) without refrigeration. But your girlfriend has mixed up 2 different concepts. It is bad to whack warm food in the fridge purely on energy grounds as it needs more energy to cool it. Unless your kitchen was very warm there would be a negligible difference in actual bacteria growth. I agree with you, you are far more likley to leave it long after it gets to room temperature or indeed forget it if you leave it out. So whack it in the fridge.
There seems to be quite a cultural difference between US and Irish hygiene rules on this subject. While it would be easy to think in terms of "primitive" and "advanced" (honestly, somone once explained their hyper vigilance with regard to bugs using this terminology) I think it simply reflects how far each is from really fresh food sources. IMHO, food is more processed in the US and has farther to travel to get to your plate. It is probably wise, therefore, to be that bit more careful.
posted by Wilder at 3:17 AM on January 25, 2006

Your girlfriend has it totally backwards. Bacteria grows in warm, moist environments, so the longer your food is warm the more opportunity bacteria has to feast on it. It is best to put warm food directly into the fridge — do not let it cool beforehand.

That said, she may be thinking of the container issue. If you have glass shelves in your fridge, or you cooked something (say a quiche) in a glass plate, you should transfer the food into a container that is NOT warm.

Put a hot pot on a cold glass shelf or put a hot glass plate in the fridge and the sudden change in temp could cause the glass to shatter, and then you'd have no leftovers at all.
posted by Brittanie at 3:17 AM on January 25, 2006

Very interesting question; my family (from The Netherlands) also insists on cooling everything off -often using cooling elements or placing the pans in question in a sink with cold water- before putting them in the fridge or freezer. That can take hours.

They have no sensible explanation why they do it, but they are extremely adamant that whacking warm things in either fridge or freezer is not good for the food.

The container is not the issue, because tupperware and tupperwareish containers aren't likely to be damaged by this process.

Not a very helpful reply, I know, but I thought it was important to add that it's certainly an international thing.
posted by Grensgeval at 3:23 AM on January 25, 2006

Not sure how "Irish" it is but that's what I was always taught to do and thought it was down to germs or something. I think I'll just start sticking food straight into my fridge now.
posted by twistedonion at 3:37 AM on January 25, 2006

Best answer: Aha! I have phoned around a bit (they already think I'm weird, now they are worried) and did in-depth interviews with my family about this issue.

They were able to give two very sensible reasons:

1) Chucking warm/hot things in the fridge or freezer raises the temperature of the other foods too much, maybe even to the point of partially defrosting them. Not good.

2) The idea is to cool a warm thing down, right? Well, the fastest way -so they insist- on doing that is not by putting it directly in the fridge, but by (see my post above) placing the container in a sink with cold water (with on the bottom a few frozen cooling blocks) and stirring the soup/food around, so there is no warm pocket in the center.
This ensures the fastest cooling possible, much quicker than air-cooling like a fridge or freezer does.

Now, as a MythBusters aficionado, I know that they are right - and if you want to speed up the cooling even more: add salt to the cold water.
posted by Grensgeval at 3:42 AM on January 25, 2006 [1 favorite]

Best answer: Okay, after some Googling - forget that Irish anecdote.
From here [pdf]
3.3 As in the case of cooking, the growth of bacteria during cooling depends on the temperature, the time, and the nature of the food (pH, salt content etc.). For example, bacteria also have a pH and a salt range over which they can grow. There is an optimum value for maximum growth and then, as with temperature, growth slows towards the extremes of the range. Hence, as the pH moves towards the lower part of the growth range for a bacterium, the bacteria may grow slowly even at its optimum growth temperature and probably not at all beyond a very narrow temperature range around this optimum value. The presence of acids as well as the physical structure of the food can also change the bacteria’s ability to grow. For the consumer it is very difficult to understand the complex inter-relationship of the nature of the food and temperature to determine a safe cooling time. Therefore, generalised recommendations have been made. Often the temperature range of 63°C to 5°C is considered to be the ‘danger zone’ in which bacteria have the greatest chance of growing but as can be seen from Table 1 this could be narrowed down still further to 55°C to 5°C. Furthermore, it has been recommended that food should not remain in this ‘danger zone’ for longer than 2 hours. However, this is a very conservative time period since we are taking the extremes of the growth ranges for harmful bacteria into account in combination with the fact that other conditions for bacterial growth in the food are rarely optimal. Considering these facts a true ‘danger zone’ with a restriction of 2 hours has been suggested as lying between 55°C and 15°C.

posted by tellurian at 3:44 AM on January 25, 2006 [1 favorite]

Best answer: A website called eHow seems to agree that cooling is unnecessary:

How to Store Leftovers
How to Refrigerate Foods Safely

Selected Quotes:

Refrigerate leftovers within 2 hours of the time they were prepared.

Cool food in the refrigerator instead of on the counter.

It is fine to put hot food in the fridge.

I was always told you had to cool stuff, though was always unsatisfied with the explanations. I seem to remember mutterings about how the rapid temperature drop causes the bacteria to get frozen, rather than killed, only to reawaken upon warming-up. Also, that the warm food would spead bacteria to the cold food. None of which really made sense. A weight has lifted from my mind.
posted by MetaMonkey at 4:03 AM on January 25, 2006

After some consideration of your quandary I realise this is not a scientific thing. I once had a three day disagreement with my partner on the fibre content of white versus other bread. I now buy white for me and the other for her. Neither of you will be happy unless you portion out the leftovers and refrigerate them as you see fit.
Does refridgerate really lose the d?
posted by tellurian at 4:06 AM on January 25, 2006

I would say that rather than a US / Irish difference this is more likely a big fridge people / small fridge people difference. I have a little tiny fridge that fits under my kitchen sink, and if I whack a great big container of hot leftovers in there, all the other food is going to suffer. There's just not enough "cold" in my fridge to counteract the effects.
posted by hazyjane at 4:29 AM on January 25, 2006 [1 favorite]

Response by poster: Note: I don't really plan on using any of these arguments in the future... trying to argue this with my girlfriend to prove that I'm right will just lead to her being pissed off at my know-it-all attitude :) I'm just glad to know that I was, in fact, right.
posted by antifuse at 4:29 AM on January 25, 2006

Alton Brown talked about this a bit in his stock-making episode True Brew IV: Take Stock. He warned against putting a pot of hot stock in the fridge because it would turn all of your other food hot and cause it to spoil, and recommended putting it in a large cooler filled with ice until it was sufficiently cooled.
posted by tastybrains at 4:48 AM on January 25, 2006

tellurian - yes it does
posted by altolinguistic at 4:52 AM on January 25, 2006

I usually let stuff cool before putting in the frig, but not for bacteria reasons. I just hate when the steam from hot food gets trapped in the container and turns to water.

Never had a bacteria problem, though I have accidently left food out over night once or thrice. In those cases it goes in the trash.
posted by Brandon Blatcher at 5:17 AM on January 25, 2006

I was told that you had to allow food to cool to room temperature so as to avoid putting extra strain on the fridge. Not because it would use more power, but the fridge would have to work harder to maintain the temperature.
posted by riffola at 5:17 AM on January 25, 2006

tellurian: Does refridgerate really lose the d?
altolinguistic: ... yes it does

Interesting: "fridge" is actually the modern colloquial shortening of "refrigerate". According to the OED, the first uses of "fridge" are from: the late 19th C (thought to be derived from the brand name "Frigidaire"), the 1920s ('frig) and 1935 (the first appearance of "fridge"). "Refrigerator" goes back to the early 17th century, and "refrigeration" (actually "refrygeracion") to 1471.
posted by bright cold day at 5:22 AM on January 25, 2006 [1 favorite]

Best answer: Arguments with girlfriends should of course begin with the realisation that you are wrong.

With a little bit of maths you could probably come up with an equation that modelled the likely level of general warming of your particular fridge for food containers of a particular size and temperature. You could then estimate cooling curves for the introduced food, warming curves for the fridge as a whole, and the difference in energy consumption between the case where food was introduced to the fridge versus where it was not. You could analyse different types of bateria multiplication rates and you could account for different rates of heat transmission by containers of difference volumes and compositions. In a couple of weeks you could model the whole thing as a computer program and take her through it step by step.

Then you would be really wrong.
posted by rongorongo at 5:27 AM on January 25, 2006 [3 favorites]

Best answer: I'm with Alton Brown on this one, though it has a lot to do with how much food we're talking about. A pot of still half boiling stock? Not going anywhere near my fridge. A bowl of lukewarm soup, sure, throw it in the freezer. A fridge or freezer is a small, contained system, and it doesn't have infinite capacity for cold. Throwing significant amounts of hot stuff in will raise the temperature of things around it, allowing for bacteria growth in the case of the fridge, and damaging the texture and increasing freezer burn on things in the fridge.

As a result, I cool things if there's more than a single serving leftover, before putting them in the fridge. Often, if I'm serving them out on plates or into plastic containers, the mere act of serving them gives them enough time and exposure to cool enough. I usually try to put anything warmer than room temperature in the fridge before it goes in the freezer.
posted by jacquilynne at 5:32 AM on January 25, 2006

I differentiate the fridge and the freezer. I might put hot food in the fridge but never the freezer - it'll defrost the stuff that's next to it! Also, stuff like sauces develop weird humps and bulges if you put them in the freezer hot.
posted by CunningLinguist at 5:38 AM on January 25, 2006

Do you use antibacterial soap on your hands every time you poop? Do you scrub long enough to kill everything? If not, you're probably doing more to potentially infect people with a serious disease than you'd ever do by letting BOILED food cool at room temperature. This is sheer paranoia.
posted by rxrfrx at 6:32 AM on January 25, 2006

I was once told that if hot things cool down quickly the texture would change somehow. I didn't really believe it, but I still usually let very hot things sit a bit before putting them in the fridge.
posted by amarynth at 6:51 AM on January 25, 2006

bright cold day - so I was wrong, it's the opposite! Cool.
posted by altolinguistic at 7:11 AM on January 25, 2006

If I could mark a "Best Answer" in this thread, it would be jacquilynne's.
posted by briank at 7:28 AM on January 25, 2006

I learnt in my food technology GCSE (oh yes) that putting warm food in a fridge or freezer could raise the temperature inside to an unsafe level, and put all the other food at risk.

From notes I just dug up:

"To preserve food properly, it must be quick-frozen, meaning it must pass through the freezing zone (0C to –4C) within 30 minutes. "

I guess if the freezer has been warmed up, that won't happen.
posted by Orange Goblin at 7:34 AM on January 25, 2006

Interesting thread; wanted to chime in that I too was taught that food needed to cool before placement in the refrigerator (and have had no problems). My parents were pretty much African bushmen though - most definitely not Irish. I suppose it's high time to change my ways.
posted by youarenothere at 7:45 AM on January 25, 2006

I just want to point out that if it were a question of fresh v. processed food, the processed food would be less likely to grow stuff. That's why McDonalds fries last forever, while In-N-Outs go moldy in a day. The processing kills things.

Also, you people have severe problems. What kind of crappy fridge do you have that warm stuff warms the other food?
posted by dame at 7:49 AM on January 25, 2006

I learnt in my food technology GCSE (oh yes) that putting warm food in a fridge or freezer could raise the temperature inside to an unsafe level, and put all the other food at risk.

And interestingly enough, I learned in the food safety class that I had to take before a summer job one year that you should put food immediately in the refrigerator.

Even the food safety people can't agree.
posted by gaspode at 8:15 AM on January 25, 2006

My parents (from England) will put cooked chicken carcasses in the oven or microwave instead of the refridgerator to eat the next day (so the cat doesn't get them). So far no one has ever gotten sick.
posted by blue_beetle at 8:17 AM on January 25, 2006

I seem to remember mutterings about how the rapid temperature drop causes the bacteria to get frozen, rather than killed, only to reawaken upon warming-up.

You have two choices, 'frozen' or 'multiplying'. You can't kill bacteria by cooling them.
posted by delmoi at 8:18 AM on January 25, 2006

I suppose this could be a holdover from when fridges were made with big chunks of ice, and while you won't waste much electricity cooling something down, you would have much less heat-absorption with just ice.

FWIW, Cooling 2 liters of water (i.e. a big stew, since most of the rest of the food is just water at a molecular level) from 300°F to 50°F would require removing about 130 Joules of energy. Even if you assume 50% efficiency, that's the equivalent energy of using a sixty watt bulb for four seconds

So it's very unlikely that putting warm food in the fridge would have any effect on the surrounding food if you have in any way decent refrigerator.
posted by delmoi at 8:25 AM on January 25, 2006

Best Answer: rongorongo
posted by jacobsee at 8:26 AM on January 25, 2006

Response by poster: Some interesting answers in here... I didn't think this would get so many responses!

I should point out... even though I mentioned the freezer, most of our disagreements are about putting leftover food in the fridge, in tupperware containers, AFTER WE'VE EATEN DINNER. So it's not like this stuff is still bubblingly hot, it's just warm to the touch. But still, it stays on that counter until you can't detect the slightest bit of warmth!

Of course I, like most guys, have learned the easy way to deal with situations like this. Say "Of course dear, you're right" and then go to the internet for our validation. :)
posted by antifuse at 8:34 AM on January 25, 2006

I'm not sure how this fits in here, but I recall distinctly, years ago while cooking at a restaurant, we'd made 60 gallons of gumbo and put it in the cooler in 5 gallon buckets. The next morning, the gumbo was spoiled and bubbling...just bubbling in the buckets like a slow simmer. Some strange process had occurred in the cooler overnight. From that point on we let the gumbo cool completely before putting it into the cooler.
posted by wsg at 8:54 AM on January 25, 2006 [1 favorite]

I agree with delmoi that this is a holdover from when people had ice boxes. It seems that ice boxes never got really cold, just cool, and putting in hot food could noticeably raise the temperature and cause the ice to melt faster. At least that's what my grandmother told me. My grandmother, whose family didn't get an ice box until she was in her teens, was adamant about leaving food to cool on the counter before putting it in the fridge, and so my mom also did this, even though her family had an electric fridge.
posted by luneray at 9:08 AM on January 25, 2006

Best answer: You and your g/f are both right, sort of. But I think she is more right.
From my microbiology textbook (c)2004:
Danger zone temperature: 60-130 degF
(Rapid growth of bacteria)

A line graph: Rate of cooling for a 2"deep container of rice VS. a 6" deep container of rice (both were hot and placed into a fridge that was kept at just above 30degF) shows:
2" deep took about 1 hour to cool down to appropriate temp. (it spent only 1 hour in danger zone, which is good)
6" deep container took over 5 hours to cool down (over 5 hours in danger zone leaving plenty of time for microbes to multiply)

If you place food in a (deep, especially) container with a lid on it, the lid will act as insulation. The best thing to do (my microbiology instructor also strongly supported this) is to leave your food on the countertop for 20-45minutes (no more than 2 hrs) to cool down and then place it in the fridge. This means it can lose the heat more quickly instead of having a battle of temperatures in the fridge for 5 hours.

Of course your way won't cause foodborne illness every time as there's all these different factors affecting the outcome, and you may have an "iron gut." I think you are rolling the dice for diarrhea.

By the way, delmoi is right. You actually can preserve bacteria by freezing them. Only sufficient heat or some kind of antibiotic or other chemical will actually kill them.
posted by mojabunni at 10:05 AM on January 25, 2006

My mom taught me to let stuff cool. I grew up in the 60's, in Michigan. Not Irish. I was taught more recently that the thought on this had changed, and now the 'approved' (Dep. of Agriculture?) way was to put warm stuff in the fridge.

My understanding of the old thought was the matter of condensation. A patina of water condensed on the food is very good for bacterial growth.

I am fairly certain the only safe thing is to live in a bubble and eat sterile chemicals. But as a child I rolled around in the dirt of the earth and ate unwashed carrots, fresh from the ground. Bugs are advised to steer clear, my immune system is fully actuated.
posted by Goofyy at 10:44 AM on January 25, 2006

Most bacteria that grows aerobically on food at room temperature is relatively harmless, except for fecal coliforms (but you did wash your hands after pooping, right?). I generally don't refrigerate food if I know I'll be eating it again the same day.
posted by randomstriker at 12:31 PM on January 25, 2006

Grensgeval, how is adding salt to the water bath supposed to cool things down faster, to any significant degree? Are the cooling blocks you refer to actual exposed blocks of ice? If they aren't, then the salt is going to make next to no difference.
posted by Good Brain at 1:09 PM on January 25, 2006

One time I put a hot pot of soup in the fridge and it shattered the glass in there...d'oh! Be sure to use a trivet.
posted by pepcorn at 2:08 PM on January 25, 2006

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