Hot leftovers straight into the fridge?
September 15, 2018 7:29 PM   Subscribe

I was taught to let leftovers cool to room temperature before putting them in the refrigerator or freezer, but it has occurred to me that I have no idea why. Is it for food safety reasons? Is it to help the tupperware last longer? Is it to save on refrigerator electricity bills (this seems the most plausible, but how much of a difference would it actually make?)? Is it something else entirely? Or is it just one of those entirely baseless pieces of "wisdom" that gets passed down forever?
posted by 256 to Food & Drink (18 answers total) 4 users marked this as a favorite
Hot food can heat up the fridge too much and make all the other food too warm to be safe. If it goes in the fridge at room temp, it gets down to 40F much faster and doesn’t raise the temp on anything else. The goal is to keep everything out of the danger zone as long as possible.
posted by blnkfrnk at 7:33 PM on September 15, 2018 [9 favorites]

Unless you're putting a ton of boiling liquid into the fridge, it should be able to keep up with the change in average temperature. The belief might go back to when refrigerators were less powerful.

As far as food safety, the USDA says you're fine. In fact, the faster the better.
posted by Candleman at 7:42 PM on September 15, 2018 [11 favorites]

blnkfrnk is correct, but...

You can get a fridge thermometer to be sure, but in my personal experience, the only time I had the fridge temp rise enough to come close to being a problem was when we were trying to put in 20 servings of soup, partially cooled (but still pretty hot) in individual-serving-size containers, in the fridge (staggered).

The fridge temp went from just over 0 degrees C to just over 3 degrees C. 4 degrees is the traditional beginning of the 'danger zone' and the max recommend fridge temp.

So, if you're cooking in bulk or have an old or ailing fridge, it can be a problem. Get a fridge thermometer and in the vast majority of situations you'll be fine, and if you aren't fine, the fridge thermometer can help warn you if you check it.
posted by flibbertigibbet at 7:46 PM on September 15, 2018 [1 favorite]

I was told it was that the water in the food will condense into droplets instead of staying evenly distributed. I’m not sure I believe it, but that’s what I was told.
posted by Tell Me No Lies at 7:47 PM on September 15, 2018 [3 favorites]

Yeah, I am pretty sure that outside of a bulk-cooking/restaurant situation, you should be fine, especially if you are breaking it up into smaller servings and not just putting a boiling stockpot or sheet pan of hot casserole in there. The NYC food handling license (and, I believe, ServSafe in other states) does advise letting items cool for no more than 2 hours, but I guess it’s not as applicable in a home setting. Unless you are working with a dorm fridge or a literal icebox.
posted by blnkfrnk at 7:56 PM on September 15, 2018 [1 favorite]

I was raised to do this, maybe refrigerators used to be massively less efficient? I believe the current thinking is to refrigerate leftovers promptly.
posted by theora55 at 8:21 PM on September 15, 2018 [1 favorite]

When I *do* cook in bulk with the intention of putting it in the fridge or the freezer, I cover the item and let it cool down to at least warm before putting it in the fridge. I don’t put it in while it’s still hot. It can also help to transfer the dish to a metal bowl, which is then placed in an ice bath (fill sink with ice cubes and water) to speed cooling.
posted by Autumnheart at 8:23 PM on September 15, 2018 [2 favorites]

You should refrigerator leftovers promptly.

In food service, people do sometimes cool the food outside the refrigerator first. But they cool it actively. They put a pot of soup into an ice water bath and stir it to cool it quickly. Sometimes there's a tool that looks like a hollow cricket bat; you fill it with water, freeze it, and then stir it through the soup. I unfortunately only know this tool as "the popsicle," which probably isn't the real name.

Or you might spread rice out onto trays in front of a fan and then repackage it more compactly, because the center of a 20L cambro of rice would take hours to cool.

If you're only making five to ten servings at a time this isn't really an issue.
posted by meaty shoe puppet at 8:28 PM on September 15, 2018 [9 favorites]

If you're only making five to ten servings at a time this isn't really an issue.

Dude, I'm talking about one to two servings of leftovers, but a voice in the back of my mind tells me that me and my family will all die if I put it in the fridge while it's still hot.
posted by 256 at 8:33 PM on September 15, 2018 [3 favorites]

>a voice in the back of my mind tells me that me and my family will all die if I put it in the fridge while it's still hot

It's the opposite, actually. The longer it's left out to get down to room temp, the more opportunities it has for airborne bacteria or bacteria that wasn't killed by cooking to colonize and start breeding at their favorite temperatures.

If you put hot food in a covered container into the fridge, it'll probably have condensation of water in the container. It'll temporarily bring down the overall temperature of your fridge, but modern (like, since the 1990s at the least) fridges will make up for it by kicking out some extra cooling to normalize the fridge.

Putting hot food in the fridge is less likely to make anyone sick than letting food cool on the counter and then putting it in the fridge. HOWEVER, letting food cool for an hour or so and then putting it in the fridge is also extremely unlikely to make anyone sick either, unless your food is woefully undercooked, or you live in a place where disease-ridden insects immediately flock to your cooling food to lay their eggs, or passing animals might lick your uncovered unfrigerated food, or parasite- or virus-ridden people with poor hygiene handle your food while it's cooling, or mold runs so rampant in your house that things left out for a day grow visible mold colonies.

It's POSSIBLE that bacteria or other nasties present in your food may have survived cooking that can make people sick and that will proliferate post-cooking... but that's even more likely to happen if you let it cool slowly on the counter rather than rapidly in the fridge. If anything survived cooking temps, it will still grow, just more slowly at colder temps.
posted by erst at 9:07 PM on September 15, 2018 [11 favorites]

My mother grew up with a literal icebox, and she believes this advice has been passed down all the way from those days. If you put something too hot in the icebox, the ice would melt, which would be a huge problem. So it’s totally fine for normal amounts of food in a modern refrigerator.
posted by Missense Mutation at 9:16 PM on September 15, 2018 [1 favorite]

This is an example of knowledge that has been twisted and misinterpreted, leading people away from a safer choice! Yes, you need to cool your food, but no, in the example you've provided, you probably should not leave it out until it comes to room temperature, unless room temp is cool (below 70*F) and the food will get to that temperature quite rapidly.

This has to do with cooling the food fast enough to get certain foods out of the Temperature Danger Zone (140-40* F). It is absolutely not that it's better for food to cool slowly on the counter, but rather that putting it in the refrigerator may not get the food down to a safe storage temperature fast enough. Any hot item should be brought to below 70*F within two hours, and then to 40* in another 4 hours, to prevent bacteria growth. USDA doesn't advise leaving any hot foods out at room temp for more than two hours if you plan to eat them again, and one hour if it is hot out!

It sounds weird because we are mostly used to small servings of things in a large refrigerator, but an item can sometimes cool faster outside the fridge, especially if it is going from, say, a shallow pan to a deep plastic container. On top of this, large quantities of hot food can still raise the temperature of an entire fridge, bringing other things into the TDZ.

Often, when cooling outside the refrigerator is mentioned, it isn't just leaving it out to cool, but actively cooling it in an ice bath, using a chilled paddle, or pouring it into bigger, shallower containers to increase surface area and therefore decrease cooling time.

Long story short, in your home kitchen, putting your leftovers away immediately is the safest choice unless you are putting a big pot of something straight from the stove into the fridge. You're really only risking condensation by popping your Gladware straight in from the pan after dinner. If I am batch cooking or otherwise have hot/warm leftovers, I put them into the smaller storage containers, let them sit just long enoug to avoid big drips of condensation (15 min or so), then put them in the fridge.
posted by assenav at 10:40 PM on September 15, 2018 [27 favorites]

The danger zone is between 6 and 60 degrees celsius and it's not recommended that you leave food in this temperature range for more than four hours over the life of the food, so just keep that in mind and you will be quite safe. I personally leave food out for 30-60 minutes to cool before putting it in the fridge.

If I am planning on freezing the food, I divide into portions and make sure it's closer to fridge temperature before freezing. The reason for this is that in the food safety class I did, the instructor said that if you put food in the freezer which is too warm, the outside of the food will freeze more quickly and will form a kind of case around the warm middle which might then stay too warm for too long. This would be more of an issue with large portions of food than smaller portions.

As already mentioned above, the reason behind not putting hot food in the fridge is to avoid raising the fridge temperature. But if you are only putting a small amount in there and it is portioned out, then it will not raise the temp too much and it will cool down quite quickly without causing a problem. You will probably get condensation on the lid of the container though, which can be annoying, and it might not be good for the life of plastic containers to be putting hot food in them.
posted by kinddieserzeit at 1:48 AM on September 16, 2018 [1 favorite]

*Long story short, in your home kitchen, putting your leftovers away immediately is the safest choice*

This is absolutely correct, for the reasons given.

I don’t know why the ‘cool it on the benchtop’ thing took hold, but it’s a myth.
posted by Salamander at 4:02 AM on September 16, 2018

I put hot food directly into my fridge all the time, have for literally decades, and no one has ever gotten sick because of it.

(One exception: When I make an enormous pot of stock I'll try to cool it down quickly in a cold water bath in the sink first, so I can then fridge it and later remove the fat and freeze it in ziplock baggies for later use.)
posted by 168 at 7:03 AM on September 16, 2018

One thing that has changed dramatically since the time when this was "conventional wisdom" probably for a good reason: materials science. If you put a hot or quite warm glass or ceramic baking dish onto a cold refrigerator shelf, you run a risk of either/both shattering.

But fridge shelves are damn near bulletproof now, and you're likely using food storage rather than going straight into the fridge with the cooking vessel.
posted by Lyn Never at 8:03 AM on September 16, 2018 [2 favorites]

The reason I don't put hot food directly in the fridge is because the air inside the sealed container will dramatically decrease in volume. With inexpensive Tupperware, this can matter. So for me it's really about sealing the container rather than cooling the food.
posted by dbx at 8:28 AM on September 16, 2018

My mother was an early adopter of the electric refrigerator; she was so quick to put leftovers away that you had to speak up promptly if you wanted a second helping. That may be because she remembered the days before antibiotics.

According to the USDA, you should throw out cooked food after two hours at room temperature, or one hour if room temperature is over ninety degrees. The problem is that the time is cumulative; the clock doesn't reset when you put the food in the refrigerator.

What I do is exactly what 168 described, but I will wait to cover a container if I think there may be some condensation. As far as leftovers are concerned, they've been out for a while during the meal, so they go straight in. A large pot of soup or stew may need to cool a bit first; the stockpot goes straight into a sink full of cold water.

Nothing has exploded yet, but I did manage to crack a plastic container by putting it in the freezer full of cooked rice. There's a similar container full of rice in the freezer right now; the convenience is worth the risk.
posted by SereneStorm at 2:59 PM on September 16, 2018

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