My mother and my sisters have always held this belief:
BELIEF: If you have some food that’s still warm, especially meat (including poultry), and you store it in a closed container and put it in the fridge, it will turn sour. To avoid this, you should leave the container lid at least partly open in the fridge, until the food is cold enough.
SECONDARY RULE: Ensure that it’s not on a solid (glass) shelf in the fridge, but on a metal shelf that lets cold air circulate underneath.
They are not alone in following these rules, in my region.
Is there any basis to this? What does “sour” mean in this context?
Cooling hot food in a closed container will condense out some liquid that will settle on the food. In an open container, the same condensation will be removed by the fridge as it maintains a very non-humid environment. So there is a legit difference between container opened or closed.
Open will result in more dried out desiccated food, more transfers of odors into the open container from other food, and more transfer of odor from this food to anything else open. A closed container has no smell transfer either direction and retains more of the foods moisture in the container and in the food.
Whether wetter or drier is better probably depends on what food we’re talking about. But none of that has anything to do with “sour” by which I assume they mean “spoiled” as in “dangerous to eat”.
There is a theoretical difference between a glass or wire shelf. It’s real unlikely this matters except in the most marginal situation where you’re already at great risk for spoilage. Which is better is also arguable depending on the airflow pattern in the fridge vs the particular shelf.
Ultimately there is a small pebble of actual sense in the middle of their giant boulder-sized snowball of bullshit.
A giant cauldron of something that’s hot will take a very long time to cool down to fridge temp all the way through the body of the food. If enough of the bulk food spends too many hours in the danger zone between 140F & 40F, it may develop contamination. To prevent spoilage you want the food to cool quickly.
The best way to do that with a big bulk is to package it in a larger number of smaller shallow containers. Not one giant bucket. See here:
In the old days, fridges might have struggled to keep everything cold if you put a large amount of something hot in them - so doing this could raise the fridge temperature for a while and cause other things in there to spoil quicker (in theory).
As I understand it, that’s not generally an issue with modern fridges, as long as the amount being added is smallish in volume (like a few portions in size).
But old habits die hard. I get people yelling at me about this in my cooking videos, even when I don’t actually do it. As well as people saying that putting metal containers in the fridge will create toxic metal poisoning (like a steel can is going to transmute into cadmium or something)
Also an issue with something like picnic coolers. But yeah, according to everything I’ve heard, it’s a myth that it’s somehow safer or better for the hot food itself to leave it out of the fridge until it cools to room temperature.
If anything, putting a lid on the food right away will make it less likely to spoil. Spoilage mostly comes from some sort of organism (such as mold or bacteria) growing in/on the food, and those organisms aren’t spontaneously generated. They come from spores in the air that settle on the food, and the sooner you cover the dish, the less opportunity that has to happen.
Food hygiene standards usually limit the time that a food is in the ‘danger zone’ for bacterial growth - so it probably makes sense in terms of power usage to leave the food out to cool from boiling, until it dips into the danger zone (and maybe a while longer), then cool the rest of the way in the fridge
There are 2 reasons to let food air-cool to room temp before refrigerating it:
Prevent water condensation. Putting warm food in a sealed container in a refrigerator allows condensation to develop. Condensation drips on the food and runs to the bottom of the container, creating a kind of broth that’s ideal for bacterial formation.
Food should spend as little time as possible in the “danger zone” temperature of bacterial formation. Sealing it immediately will trap the heat inside and allow it to stay in the danger zone longer (with above-mentioned condensation making matters worse).
So keep food loosely covered so heat and moisture can escape, and seal and refrigerate immediately when it’s reached room temp. I do this on the countertop, not in the fridge, but in the fridge should be fine (might be better, except it may warm the other food)
As far as the storage surface, either a metal grille or a glass shelf is fine. The grille allows air to circulate around the container, but the glass surface will serve as an equally good heat sink. A bad choice would be setting it on a dish towel or wooden cutting board or other insulator. Metal bowls are very good.
This is the main reason that I let food cool on the counter before I refrigerate it. Depending on the food, the condensation can make it soggy or watery.
What’s the point of keeping it loosely covered? Wouldn’t it be better to keep it completely uncovered so it will cool faster? (Absent any known insects or hungry pets, of course.)
No one has yet commented on the “no glass shelf” rule. I wonder if that comes from “cold glass may crack when plunged into hot water, or maybe vice versa, I don’t remember, so just don’t put a hot container on a glass shelf I guess.”
If you only care about cooling it fastest, then leaving it completely uncovered is ideal. However there are also a lot of bacteria-carrying particles circulating in the air that can settle from above.
I find that paper towels are good for this. Because they are rolled, they form a natural arch over the top that prevents dust settling from above, but allows moisture and heat to escape from the sides (and somewhat through the paper). But sometimes I’ll just leave the plastic lid on loosely and cocked to the side.
Just as a data point, my wife will leave food sitting open and uncovered on the countertop for 2-3 hours. I think this is acceptable for veggies and grains, but I’ve argued vigorously (and unsuccessfully) that this is a bad idea for most proteins and soups.
However, the truth is that her way has never caused any undue spoilage, and arguing is stressful. So I just let her do her thing, leaving everything uncovered like a petri dish, and quietly make sure it doesn’t stay out a moment longer than it takes to cool down to room temp (like 30 mins). But if it’s soup or protein I’ll definitely cover it with a paper towel when she’s not looking.
Yeah, I suspect this is the reason for that rule, and there is some truth to it. If a pot is sufficiently hot, it theoretically could crack the glass. It’s the same thing that happens to the idiots who pour boiling water on their windshield to melt the ice.
I thought the “leave the lid off” rule was to prevent the growth of the really bad anaerobic bacteria like botulism which could flourish in the time before the food is fully cool while the lid prevented enough air circulation to stop them.
Cover leftovers, wrap them in airtight packaging, or seal them in storage containers. These practices help keep bacteria out, retain moisture, and prevent leftovers from picking up odors from other food in the refrigerator. Immediately refrigerate or freeze the wrapped leftovers for rapid cooling.
Hell, I just leave it out there. I love the extra shelf space winter gives me, as we have a counter-depth fridge, so space is at a bit of a premium. I mean, I can take them out of the dutch ovens into more sensible containers, but when I could just stick the darn thing out there and forget about it? Awesome.
My high school chemistry teacher (from ~40 years ago) told us never to buy dented food cans, and never to put food cans in the fridge. Dents are bad news as this can damage the coating inside the can, leading to corrosion leaching into the food (really bad news in the days when this coating was tin as galvanic effects accelerate the corrosion and produce toxic tin compounds). The fridge thing also dates to when cans were lined with tin, as the allotrope of tin at fridge temperatures and below is less dense (i.e., expands when cooled) and is weaker and prone to crumbling.
Thankfully food cans are lined with somewhat less toxic (at time of writing) plastic these days, but I still don’t buy dented cans or put them in the fridge… just in case.