I tend to keep condiments and things of that nature for a very long time in my fridge even though most Google searches say use within 3-5 days after opening. How can a sauce or can of broth or any other shelf stable thing last for months, if not longer, in my pantry, but if I open to use it for a few seconds and put it in my fridge it’s supposed to be used with if a few days? I’m talking anything from pickles to mustard to broth. All of those items seem perfectly fine in the fridge even after weeks or sometimes months.
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Highly acidic things like pickles and mustard do last a good while open in the fridge. But the difference is they were sealed at temps bacteria cannot survive/ in a sterile environment. Once you open it in your home that’s chock full of bacteria, those bacteria are now inside of it and can start the spoiling process. Anyone telling you mustard only lasts 3-5 days after opening is crazy. But they do spoil much much faster after opening because the bacteria is now in there. Can of sauce is probably the easiest to observe for yourself. Lasts months in the pantry no problem. Leave an open can of tomato sauce in your fridge for a month. It will be moldy and gross.
When a can is sealed, typically high heat is used. So the food is sterilized *and* vacuum sealed. There’s no way for bacteria or even more air to get inside. Same thing with boxes, pouches, etc. A lot of times when those are sealed, a gas like Nitrogen is blasted inside. Bacteria and other organisms need oxygen to survive, so replacing the air with something that isn’t oxygen makes it likely they stay fresh. (There’s a few exceptions, some foods are susceptible to bacteria that thrive without Oxygen, nature hates rules.)
When you open it you break that seal. Not only can oxygen get inside, but you could have dust or other particles in your house carrying a tiny amount of bacteria. Every hour that bacteria multiplies, and after a while there can be enough to make you sick.
Things that are fine for a long time tend to have reasons they’re bacteria-resistant. For example, honey has very little water inside so bacteria has a hard time living in it. Refrigerator temperatures slow down bacteria’s rate of multiplying, so it can make things last longer. Pickles… I’m not usually used to those having a short life in a jar, at least. Usually they’re sitting in a brine solution. That’s one of those “bacteria-resistant” things I mentioned, it’s a super salty/acidic liquid and that’s just not a place bacteria grows well. Lots of off-grid people pickle vegetables because it helps keep them from spoiling.
The food can seem fine. The “use by” dates are safe margins. They look at how fast the likely bacteria CAN multiply, then how much of it usually makes people sick, and pick a date way before that “makes you sick” date just to be safe. If you eat it past that date and get sick, that’s on you. They have to pick a date that’s safe enough nobody can sue them. So they err on the safe side. That’s the point of the laws that make them calculate the date. Back then we felt like if hundreds of thousands of people got food poisoning that’d be bad for the economy because they’d not be at work and they’d go to doctors.
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**Put even shorter:**
The factory’s job is to guarantee the food is safe. They get inspected by the government to make sure this is true. The promise is only good as long as the food is sealed.
Once you break the seal, you can do a lot of stuff that might make the food spoil faster. When they tell you “use within…”, they’re protecting themselves from you suing them if you get sick. Depending on what you do, the food can be good for a long time, but in the end they care about not getting sued so they usually pick a very short date. Once that date is up, the government is satisfied they did their job.
They do go bad because generally products like those come in sealed containers meaning that they aren’t exposed to the surrounding environment(microbes) and the factory probsbly also sterilizes them(boil in high heat). When you open them they are suddenly exposed to an environment filled with microorganisms that feed and grow on the food. Salty, Acidic environments prevent growth
short answer: the sealed pack is sterile, but thats not the case once its opened.
during manufacture, they can take various steps to ensure that the contents of the foodstuff are basically microbe free (or, at least, anything that was sealed inside them was killed afterwards). So long as the seal is good, that food wont rot for a very long time.
once you open it, all the bacteria in your kitchen can get into it, and it will begin to rot.
also, most “use by” dates and recommendations are a bit conservative, as they dont want to be liable for saying food that MIGHT be off is ok, so they underestimate on the packaging for safety.
When they are sealed, they are sealed clean. But once you open, outside germs and mold spores can get in and grow quickly due to lack of competition.
Depends kn the environment they’re kept in, but generally a 1-2 weeks for most sauces will be fine if they’re kept refrigerated.
But I also subscribe to the idea that companies write their expiration dates as early as possible to get more sales from food waste.
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