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Why do store-bought dips (guacamole, sour cream and chive, salsa...) typically say "Keep refrigerated and consume within 24 [or 48] hours of opening"?

Before opening they typically have a "use by" date of a few days to a week away from when I buy them.

Is it related to the stuff that ends up being transferred into the dip by the nachos / crudites / whatever is being dipped? In other words, if I transferred part of the dip out into a separate container using a clean spoon, would I get a longer life (more than 24 / 48 hours) out of the remaining pot of dip?

Examples:
24 hours: Guacamole
48 hours: Salsa, Sour cream dip, Cheese and chive dip

  • Do you generally find that homemade guacamole lasts longer than a day? I don't... they brown and get watery and taste funny... The salsas I buy stay good in the fridge for weeks, so not sure why yours last so little... similarly, I'm pretty sure the sour cream dips from the refrigerated section last for a week or more after opening. I don't have any around the house but that's what I remember. Could you be more specific about the exact products you're discussing? – Catija May 14 '15 at 22:42
  • I've added some examples which are either 24 or 48 hours after opening. – Vicky May 15 '15 at 8:13
  • you'll often see this on things that have been pasteurized -- they might be shelf stable for a long time, but once the package has been opened, they'll go off quickly. It's also true of things that have been packed in a low-oxygen environment. (which I suspect that the guacamole was, to prevent it from changing colors). – Joe May 15 '15 at 13:14
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I would assume that it's for safety reasons.
Not yours only, but the manufacturers' as well.

At the plant the manufacturer can control the environment and make sure that the product leaves in a condition that should last for a certain time under specific conditions ( e.g. when refrigerated). Subtract a bit for safety and you have the manufacturers best-before-date.

Once the consumer opens the sealed package, all bets are off: There is no way to know what may be introduced into the product. This may be as simple as getting oxygen to food that was sealed with packaging gas, introducing new (and ever-present) bacteria, yeasts or mold spores in a previously pasteurized pack or simply scooping with a not entirely clean spoon. Leaving bread crumbs or double-dipping is simply a very extreme example. In other words, one never knows what might start to grow after opening.

But if the product is refrigerated promtly and consumed within X hours, it may be assumed that even if something risky was introduced, the time/temperature is too short for it to multiply into a critical amount leading to foodbourne illness.

If you work very cleanly, I assume that you could extend this time frame quite a bit, but obviously won't tell you to do so - lest you or some other reader comes back complaining that I told you to and made you sick.

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