Came to think about this while eating a store bought chicken curry with rice meal. The packaging had a the expiration date on the 24th, if kept in the fridge. Meanwhile, had I stored leftovers of same food I’d have made myself, it would probably only last a few days in the fridge (especially rice, which is said to expire fast)
Hence I wonder, how do they get the food to last so long? I get it has to have something to do with better hygiene and airtight packaging, but that alone can’t make it last so much longer, right?
In: Biology
Salt and preservatives inhibit microbial growth and oxidation / other ways food degrades.
It also comes down to the way they’re prepared and packaged. They’re cooked thoroughly to kill as many germs as possible and then cooled down as quickly as possible, to minimize time spent in the “danger zone” (in which bacteria, the kind that cause food spoilage rapidly multiply) and thereby minimize the amount of bacteria present when it gets sealed up. And then they’re usually sealed immediately. That sealing is probably the biggest part after sterilization: it prevents any oxygen or moisture and other microbes from getting in. It’s why canned food can last so long, but as soon as you break the seal the clock is ticking on when it’ll go bad.
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Prepared and packaged foods have preservatives in them, and they’re pasteurized — either sealed in to airtight packaging and then heated above 140 degrees or they’re packages while still above that temp. Either way, bacteria cannot survive at those temps, so the food is sealed and there are no live bacteria, no way for new bacteria to get into the food and cause it to spoil.
Once the packaging is opened, and the food is exposed to air that has bacteria floating around then the food can spoil in a few days.
Sealed packaging does a lot of work. As in, a *huge* amount of work. Notice how many foods and sauces will have a ‘refrigerate after opening’ or ‘use within 7 days after opening’ on the label. Another part is industrial preservatives, but even without that you can achieve similar results just with proper household canning methods.
What makes most food spoil? The answer is mold (at least in our modern world of easy access to refrigeration; bacteria is usually a problem for more specific foods and/or temperatures, and pests are *much* less likely to be an issue inside a fridge).
Mold spores are *everywhere*, and the only reason they are not a constant problem to our health is that they just don’t grow well in our bodies (thanks, immune system!). But they *do* grow well in moist, lightly aerated situations, which is what most of our cooked leftovers are. Even when refrigerated, though slower than room temperature.
So industrial packaging will either use heat to kill most of the spores (canning/pasteurizing) or use alternate airs (such as nitrogen gas, a famous example being potato chip bags) before sealing the packaging for any of those ‘long shelf life’, read-to-eat foods. An alternative is having something else about the food making it hard for mold to grow (e.g. acid or salt), but I don’t think that’s the kind of food you are thinking of; these examples will usually have an expiration date that is months or years away, not just weeks.
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