It just sits there on the bench for hours...
January 18, 2011 11:53 PM   Subscribe

My girlfriend thinks it's bad to put hot or warm food in the fridge without letting it cool to room temperature first. Something something bacteria something something. I think she's stupid. I also think she's wrong. Is she?
posted by doublehappy to Food & Drink (20 answers total) 3 users marked this as a favorite

That's eerily similar and includes all the details I left out like forgotten food on the bench and the horrible run on sentence about same. I really did search for previous questions, but I was talking about a bench and a refrigerator, not a counter and a fridge! Thanks.
posted by doublehappy at 12:54 AM on January 19, 2011 [2 favorites]

After reading the other thread - it only really matters if you're putting something hot directly into the freezer. Apparently piping hot food can throw the freezer out of whack.

I usually go stove > fridge > freezer if I'm making something specifically to be frozen for later.

Also, as far as I know a couple hours sitting out won't make all that big a difference with most cooked foods, anyway.
posted by Sara C. at 1:02 AM on January 19, 2011

Here is the USDA's take on the matter. In brief, they agree with you, if you divide larger quantities into smaller packages.
posted by Orinda at 1:06 AM on January 19, 2011 [2 favorites]

I attended one of those food service classes years ago where they certify you for restaurant work per the department of health or whatever and for what it's worth the big issue there was the middle of larger portions of hot foods. We used to use an ice bath to cool the food rapidly before saving it in a fridge when I worked in a restaurant. From what I understand the core of the food (I like to think of big dishes of food like planets) can remain warm enough for bacterial growth much longer than the outside portions.

This was multiple years ago so my memory might be fuzzy. I'd go with what the USDA says, because it seems that what they're getting at is what I've been told concerning large portions.
posted by IvoShandor at 1:23 AM on January 19, 2011 [5 favorites]

The colloquial way this was explained to me is that refrigerators are good at keeping things cold, but they're not as great at making them cold, which is where the time->bacteria issue comes in.

It's more apparent when there's a lot of hot [whatever] in a single container. It's why in restaurants we'd give giant batches of things an ice bath or cold rinse to bring the temp down first(pasta), break it up into smaller portions or spread them in shallow containers(rice) to provide more surface area and so on. With big batches of soup, we'd make sure to stir the container whenever someone went into the walk-in fridge to keep the hot "core" dissipated. Once things are fully-cooled, they can them be dumped into big buckets for storage if needed.
posted by Su at 3:03 AM on January 19, 2011

Well, letting it cool before putting it into the freezer or refrigerator does save energy, since you aren't using electricity to reduce the temperature from hot to room temp. As to the bacteria question, I also defer to the USDA.

I wouldn't say she's "wrong" (or stupid).
posted by Kirth Gerson at 3:34 AM on January 19, 2011

It can be bad to put hot food into the fridge if your fridge has glass shelves - a hot saucepan (for example) coming into contact with cold glass can shatter the shelf.
posted by UbuRoivas at 3:52 AM on January 19, 2011

If your concern is bacterial growth, then you want to reduce the temperature of your food as fast as possible. If the options are putting it in the fridge right away or letting it cool on the counter, food will cool a little bit faster in the fridge than on the counter. (However, an ice bath will cool it much faster than either of those other options.)

But putting hot food in the fridge will raise the overall temperature of the fridge a bit, and the fridge will have to run a little bit to reduce its temperature back to the thermostat setting. So it's a little more energy efficient to cool the food some outside the fridge first than stick it right into the fridge.

In the end, I'd guess that the actual difference in cooling times between these two methods is negligible in terms of how it affects bacterial growth, so you could do the counter cooling for a bit in order to save some energy without any danger.
posted by dseaton at 4:06 AM on January 19, 2011

Wouldn't bacterial growth be just as likely if you left the food on the counter to cool?
posted by jasondigitized at 4:10 AM on January 19, 2011

My wife is a chef who has been to countless ServSafe courses like the one IvoShandor describes and she concurs with the USDA. It's also OK to disagree with your girlfriend but she is not going to be your girlfriend for long if you call her stupid in a public forum.
posted by fixedgear at 5:20 AM on January 19, 2011 [45 favorites]

Cook's Illustrated takes the stickler's approach and agrees with your girlfriend, for the "fridges aren't good at making things cold, just keeping them so" aforementioned reason. Meanwhile the many hours it's taking to cool your leftovers it's throwing the whole unit and all the other food in it out of whack, which is problematic when you've got, say, raw chicken in there.

They suggest baggies of ice from the freezer or a cold pack or whatever surrounding (on top of and below too) the leftover package on the counter to help speed along the cool down process so it doesn't take hours in the danger zone. That's what I do whenever I have a huge vat of hot soup or stock I need to get in the fridge in under 2 hours.
posted by ifjuly at 5:21 AM on January 19, 2011

[Despite the phrasing, this question really isn't about the girlfriend]
posted by vacapinta at 5:58 AM on January 19, 2011 [2 favorites]

I usually transfer things to a deep stainless steel insert, and then put that into a sink filled with cold water. After ten minutes or so it's usually safe to put in the fridge without worrying about bacteria, warming up other food in the fridge, or breaking shelves.
posted by chrillsicka at 7:20 AM on January 19, 2011

Small portions, like dinner leftovers, go right in the fridge.

Large batches I intend to freeze, like chili or tomato sauce, get ladled into serving size containers, put in the fridge and then later transferred to the freezer.
posted by utsutsu at 7:33 AM on January 19, 2011

To see how much it costs to transfer hot food to a refrigerator we can do a quick back-of-envelop calculation.

Take one liter of soup (1000 grams, about a quart) from 100 degrees C (boiling) to 0 degrees (just above freezing). The specific heat of water is a little more than 4 joules per gram per degree C.

So the heat transferred is

1000 grams * 100 degrees * 4 joules per gram-degree = 400,000 joules.

Let's say your high efficiency refrigerator has a coefficient of performance of 4, that is, it transfers 4 joules of heat for every joule of electrical energy. So you need 100,000 joules of electrical energy to cool the liter of soup.

A watt is one joule per second so you need 100,000 watt-seconds of electricity. This would be the equivalent of running a 100-watt light bulb for 1000 seconds or a little more than 15 minutes.

As far as cost goes,

100,000 watt-seconds/3600 seconds per hour = 28 watt-hours. Electricity costs about 20 cents per kilowatt-hour so

(28 watt-hours/1000) * 20 cents = 0.6 cents.

So we can conclude that putting a quart of boiling hot soup in the refrigerator is about the same as running a 100-watt light for 15 minutes and costs roughly a half of a penny.

If you cool the soup to around room temperature before putting it in the refrigerator you save about 2/3 of that cost.

Hey, maybe what you should do is put the hot soup in the refrigerator and turn out the kitchen light -- then you're even.
posted by JackFlash at 11:03 AM on January 19, 2011

Yes on both counts.

It's not efficient to put hot things in the fridge, but there's no (additional) bacteria concerns doing it that way. Unless of course you're putting a large, boiling hot cauldron in the fridge, in which case you'll be significantly raising the temperature of the fridge for a significant period of time.

Also, whether something is room temperature or very hot, the whole point of a refrigerator is making AND keeping things cold (unless all your stuff goes straight from the grocery store chiller to your fridge, in which case, you're doing it wrong). So use it for those things and enjoy the miracle of life in the 21st century.
posted by coolguymichael at 11:28 AM on January 19, 2011

Thanks for your answers, everyone. There's still just enough both ways to keep the argument alive on the fringes, but she's conceded the core!

Thanks also to some of you* for your cheerless assessment of my relationship's future. We wrote the question together - she threw a grape at me so I hit her called her stupid on the internet. I think we're fine. I don't really think she's stupid.

*Are you the same people that answer "What should I get X for their birthday?" type questions with "Donate $100 to charity on their behalf"? You make the world less fun.
posted by doublehappy at 4:27 PM on January 20, 2011

Throwing a grape constitutes assault & battery in some jurisdictions, and is indicative of an abusive relationship. You should get yourself a lawyer, and some therapy.
posted by UbuRoivas at 4:40 PM on January 20, 2011 [2 favorites]

I'm in New Zealand, so I can't sue for battery, and the grape hit me from behind with no warning, so I'd fail in an assault claim, too. She's also a few years ahead of me at law school, so I'd be completely screwed.
posted by doublehappy at 6:37 PM on January 20, 2011

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