Howdy all,
Hope this is the right flair.
Yesterday I discovered one of our glass Tupperware containers in the hatch of my wife’s car and the lid is sucked in on itself.
The lid has four clips that snap under the lip of the glass and it’s air tight I would assume. It has remnants of her buffalo chicken chili in it. That has dairy in it.
It’s also been relatively warm here until yesterday when I discovered it. It was 15 degrees F difference.
Thanks in advance for your answers.
In: Biology
If the lid was put on with say hot food. Like from a microwave. The air inside gradually cools, as it does it takes up less volume, as cool air is less dense.
This creates a vacuum that can “suck” the container lid closed.
Things, notably air shrink when they cool. When she shut the food in the container it was still hot and was surrounded by hot air. Once she sealed it and allowed it to cool, the air (and to some extent the food too) shrank – in particular the steam that had been in the air condensed into water and shrank considerably. This reduced the pressure inside the container so the atmospheric pressure is holding it shut.
When you heat up a gas in a closed space, its pressure increases. When you cool it down, the opposite happens. In this case the air in the sealed container cooled down, so the pressure dropped to below normal atmospheric pressure. This is a partial vacuum, so the air ‘sucked’ on the lid. If you heated up the container you would find that at a certain temperature the lid would easily come off again as the contents of the container reach atmospheric pressure.
Take a more extreme example, you have sealed it in Denver and flew to NYC. You get off the plane and try to open the container and it is hard as hell to get open. What happened? Simple, you sealed it at an atmospheric pressure of 1 atmosphere minus 1600 meters (so about .82 atmospheres) and then you tried to unseal it at 1 atmosphere. All of that air is trying to get in to equalize, since the pressure in the container is less than the outside. Now is a good time to explain a fundamental law about pressures, high pressure always tries to root out low pressure. It is why your ears pop as you go up in altitude, the air inside the ear is higher pressure and it is desperate to get to that low pressure air.
So, if you put warm food in the container and seal it, the air cools and densifies, meaning it takes up less total volume. The pressure inside the container is slightly less than outside, and the outside air really really wants to get into the container. That vacuum you feel is actually the pressure of the outside air trying to get *into* the container, which is being prevented from getting in by the airtight lid.
You can repeatedly and quickly demonstrate this with a jar candle. Light a candle and place the lid on the top lightly. As the oxygen is consumed by the flame you will see (and hear) the lid suck closed as the air pressure is reduced because the oxygen is being taken out of the air and deposited as ash.
In addition to all the right answers, it isn’t necessary that the food was hot when it went into the container.
The air inside may have started cold and got heated in the hatch of the car. These containers withstand pressure from the outside well, but not from the inside.
The heated air expanded, lifted the lid until a tiny gap opens and some of the air gets out. When outside and thus inside temperatures fall, the air cools and because now there’s less of it, the lid gets pressed on by lower pressure inside and higher pressure outside.
Hot air? Less dense
Cold air ? more dense
The process of “canning” requires heating the food containing jar to near boiling, which heats the remaining air in the jar as well. Then the lid is screwed on.
As the jar cools down from nearly 100C to room temp around 20-30c. The air goes from less dense hot air. To dense cold air. This creates a vacuum as the higher density air creates a low pressure zone. Basically there is less mass of air inside than there typically would be. So the atmosphere around the jar, pushes in on the lid.
That’s the what. But why? Well 3 reasons in a trench coat disguised as one. Bacteria. Bacteria is bad, and is what actually “spoils” your food. Food going bad without bacteria is “stale”.
So reason #1. Heating it to nearly boiling kills a LOT of bacteria. This is good.
Reason #2. Bacteria (at least the ones that hurt us) need oxygen to eat and replicate. By starving them of oxygen, by reducing the total mass of air, and therefor by extension the total mass of oxygen? You’ve forced the remaining bacteria in your food to go dormant, and not replicate.
Reason #3. Bacteria, need to eat to replicate. Just like people. When they do, their little bacteria bodies consume oxygen, and food, and emit carbon dioxide. When they do this, they increase the total air mass in the jar, and therefor increase the pressure in the jar! This happening once? Twice? A hundred times? No problem. This happening a million or billion times? You’ve got a small bacterial colony. This would hurt you. This increased the total air pressure in the jar so much that the “sucked in” lid, is actually pushed out. This serves as an easy way to tell humans that the jar belongs to the bacteria now, and we shouldn’t eat it.
A few things to note. Sorry to tell you this. Bacteria don’t hurt you! Their poop does. So when you get sick with a bacterial infection? It’s micro poop.
Bacteria farts make can lids pop
All your food has bacteria. A little? Your immune system easily takes care of it. A lot? Oh boy are you in for a world of hurt. This is because the bacteria overwhelm the antibacterial capabilities of your body, basically allowing the bacteria to out produce the white blood cells that try to take them down.
This is what C diff, and E. coli infections are. You have C. Diff and E. coli in your intestines right now! A lot of it. But your immune system, and other bacteria in your gut biome are totally capable of keeping it at bay! No issues. When the C Diff or E. coli gain too much traction, and have too large of colonies? That’s what we consider an “infection”
Introducing large amounts of this bacteria (looking at you romaine lettuce) from outside sources can cause serious imbalances.
Latest Answers