Like milk goes bad a week or two after opening it but if you don’t open it, it will stay good until the expiration date? Like yogurt, sour cream, shredded cheese. All those things. I’m confused
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Different reasons. Many things are packaged in environments without oxygen – eg in nitrogen gas. Other things are heated after they’re packaged. You can avoid contamination in different ways, or at least minimize it.
Many things stay good way past the expiration date anyway.
Many packages are filled with inert gas like nitrogen, so there is no oxygen to spoil the food.
Many manufacturing plants are way cleaner than average homes, so less mold etc. end up in the final packaging.
Things like canned food and jarred stuff are sealed, THEN subjected to heat (or sometimes radiaton), so any bacteria in the product is killed, and since it’s sealed, no more can get in.
Since all the microbes are dead, little to no spoilage of the food happens.. the problem isn’t the air, but what’s in the air.
Once you open it, you reintroduce new microbes and they begin breaking down the product.
The environment in which foods are packaged is pretty sterile. There won’t be a lot of microbes in the air. Some products are heated after packaging to destroy any contaminants that may have happened. Some products are injected with nitrogen rather than oxygen, taking away chance for living organisms to be retained.
Once you open the package, you’re introducing mold spores from the air, potentially bacteria, cross contamination, etc.
I drink ultra-high temp pasteurized milk, and it lasts a very long time even after opening because I rarely expose it to the air for more than a quick second.
Lunch meat is easier to contaminate, for example, because some meat remains in the container/bag that you’ve touched already, thereby introducing bacteria.
But anyway- generally there’s just not a lot of exposure to contaminants during the production process; and they have industrial filtering systems in place to reduce the contaminants in the air as much as possible. Items where this is harder to prevent are often heated after packaging to destroy bacteria. (Sorry now I’m repeating myself so I will stop lol!)
I’m a bacteria; a survivor. Before the hot times, me and all my brethren were eating and breathing and replicating with reckless abandon. We were innocent, then, and knew not of the coming trials.
But then the Pasteurization attacked. 99.9999% of my friends died in the heat. Luckily, I managed to squeak through, though I imagine had it been some kind of ultra-high pasteurization, I might not have made it. But I survived, and was even able to reproduce a little bit afterwards. Unfortunately, the Great Seal had cut off the air, and while my children and I used what oxygen we could to help repopulate the world, we ran out. We stopped spending so much energy, despite all the food all around us. And we waited, and prayed for deliverance. And lo, when the Giant One lifted the Great Seal, blessed air came to us once more. We gave thanks to the Giant One, and we feasted and divided as never before. After all, why would the Giant One deliver us oxygen if not to tell us to reproduce? Praise the Giant One, and let us multiply a trillion-fold!
On some products, you’ll see a note on the label that says “Packaged in a protective atmosphere.” This means that right before it was sealed, it was placed in an oxygen-free environment, so whatever air space is in the container is filled with an inert gas like nitrogen. This is done with products like bread which can’t be re-heated after being cooked, and also products that would oxidise on their own without bacterial intervention, e.g. potato chips.
Other products, often canned goods, are heat-treated (e.g. Pasteurisation) or irradiated after sealing, which sterilises the product within and the can provides the protection. I watched some fascinating YT videos on food irradiation where the operators irradiated themselves by completely ignoring the safety protocols or defeating them entirely (“Balls!”).
As others have mentioned during the packaging process they have the ability to remove all oxygen from the packaging which will far lengthen the shelf life of the item until it’s opened.
My buddy works in agricultural insurance and recently toured a new state of the art potato processing plant. Once the potatoes arrive they are cleaned and then they enter the massive building as whole potatoes, the entire building is air tight with no oxygen or light inside, the entire process is automated, first they are skinned, then cut into specific shapes/sized, dried (a few other steps in the process as well I’m sure), packaged in air tight wrap and boxed, all of which is done in a sterile environment without any light or oxygen, this drastically increases how they can last in their packaging. After this they will be shipped in either fridge or freezer trucks to distribution.
So for this example they actually haven’t been exposed to any oxygen whatsoever since they were cut, and uncut/fresh they naturally preserve for a pretty long period..
>when they clearly had to be exposed to air before being sealed?
Because when they’re sealed, they’re not exposed to oxygen. It’s either under a vacuum, or they put a gas in there. For example, Pringles tubes are filled with nitrogen. If bacteria need oxygen, and there’s no oxygen, then bacteria don’t do anything.
Another reason is that the bacteria is killed. Canned tuna or milk are examples of this. If the bacteria is killed, it’s harmless to you.
Things like chips and cookies are packaged in a dry environment.
Now once you open the container, it’s exposed to oxygen moisture and bacteria that’s floating around in the air, which will now allow bacteria to grow, food to go stale, etc.
Chiming in to add another point. I used to operate a brewery canning machine. Before being filled with beer, each can gets purged with carbon dioxide. So before the lid gets popped on and seamed, there’s a cushion of beer foam and CO2, rather than oxygen.
Lots of answers explaining a part of it, or why it works in one circumstance. But really the whole thing comes down to one strategy: **minimize the amount of stuff that causes spoliation (like bacteria and oxygen) that exists in the package**.
There are a ton of tactics, depending on what you’re packaging. But a lot has to do with sanitary environments, packaging technology (such as replacing air with oxygen in it with nitrogen before sealing the package), and post-packaging treatments (like pasteurizing something that’s been sealed, so that any bacteria is dead and there’s no path for more until the seal gets broken).
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