I had a friend who claimed that if you sealed the lid on Tupperware before the contents had cooled, the food would spoil quicker. Is this possible? I would think that sealing food when it was hot would reduce the introduction of bacteria, not encourage it.
[sarcasm] Oh, sure… and when I boild preserves for canning to sterilize everything, I always like to cool it off before I seal it, because you know how those microbes leave the food once it’s cold… [/sarcasm]
I can’t think why it would spoil faster that way, either… Could your friend explain why?
I know what your friend is getting at. You want the food to cool down fast, away from bacteria-incubating temperatures, and if you put a lid on something that’s hot, it helps it stay warm, as it prevents it from radiating quite so much heat out into the atmosphere or wherever. So, goes the thinking, you leave the lid off to enable the food to cool off faster.
However, a plastic lid doesn’t have that much insulating ability, and even a covered Tupperware full of hot spaghetti sauce will cool off pretty fast. The whole thing sounds related to that “you have to let food cool off on the counter before you put it in the fridge” thing, which isn’t true.
Also, if you try to seal a lid on Tupperware while the food is still hot, when it all cools off in the fridge it sometimes pops the seal, and you don’t realize it, so when you reach in there to take it out, the lid falls off and you get spaghetti sauce all over the place. Which is IMO reason enough to let the spaghetti sauce cool off a few minutes before you try to put the lid on.
Actually the reason you can seal hot perserves is you seal it with no air in the top of the jar. Air has germs…no air= no germs. If you seal your food in tupperware you are trapping air (germs) in the container in a nice warm cozy environment. In ideal enviroments, between 40F and 120F, bacterial will double in volume about every 2 hours. The longer it says between those temps the more bacteria grows. That’s why you should always re-heat just what you will eat not an entire pan of something that will get reheated and cooled several times.
That’s my story and i am sticking to it.
When canning, you seal jars when they’re hot to avoid contamination. The food in the jar, which has been raised to a very high temperature, is sterile. If you let the can cool down, there’s a chance that germs can land on the (now not-so-hot) food, and when you put the lid on, you’ll just seal them in.
There’s the handy side-effect that as the air cools, it contracts, so you get a nice “vacuum seal.” It’s not a true vacuum, of course. There’s still air in the jar. It’s just that the air pressure inside the jar is a bit lower than the air pressure outside the jar.
DDG’s on the mark. The problem is that the medium temperature range is ideal for bacterial growth and proliferation, and when you simply throw a lid on a container of hot food and shove it in the fridge, it stays in that range for a long time. How long, and whether it’s a problem, is usually a function of the quanitity of the food, the size and shape of the container, the temperature of the surroundings, etc. It’s especially a problem with large quantities of stuff like spaghetti sauce or stock. Simply heating up the food again isn’t enough, since with many nasties the problem is the toxins they excrete while they’re active at the medium temps – the longer they’re kicking around, the more toxins you get, and the toxins usually aren’t broken down by reheating.
When making stock, I generally try to cool it rapidly once it’s done by filling half of my sink with ice, ice packs, those blue things you freeze to use in coolers, and whatever else is available, and water. I then pour the stock into a new, cool container, and place the container down into the sink, forcing down if need be so that the ice water level outside is higher than the level of the stock inside. I then swirl the pot back and forth, stirring the ice water with my hand and the stock with a spoon occasionally, to get the whole thing cooled as quickly as possible. Once it’s cool, I’ll then pour it into smaller containers for the fridge and/or freezer.
If you have only a small container, and it has lots of surface area relative to volume (i.e., like one of those square sandwich containers or even one of it’s slightly larger but still shallow cousins), you’re probably OK – in any event, the food’s not likely to spend any longer in the “danger zone” temps than it would if you left it on the counter with the lid off in order for it to cool down. For large quantities of things in a single container, an ice bath is probably the best strategy.
Tell your friend to leave the lid off the container, but put it in the fridge.
Once it’s cool, then put the lid on. This avoids leaving uncovered food out at room temperature.
I wouldn’t actually do this myself. I just put on the lid and put it in the fridge. But it will probably satisfy your friend.