How long does sour cream last in the fridge?

The short version: unopened and kept continuously cold, sour cream is often still fine for one to two weeks past the date on the tub, because that date is a conservative quality estimate rather than a safety cliff. Once opened, the commonly cited window is about one to two weeks, refrigerated and kept covered — noticeably longer than opened milk or opened cream, because sour cream starts the clock already fermented rather than plain.

Why "cultured" buys it extra time

Plain milk and cream spoil when stray bacteria get in and start multiplying in an otherwise hospitable, near-neutral liquid. Sour cream skips that starting line: it is milk or cream that has already been deliberately fermented with lactic acid bacteria, which drop the pH low enough that a lot of the organisms that spoil plain dairy struggle to get a foothold in the first place. That is the whole reason it keeps noticeably longer than the cream it was made from, both sealed and after opening. It is not immunity, though — it is a head start. Given enough time, air and temperature swings, sour cream still spoils; it just tolerates more of all three before it does.

What actually decides how long it holds

Temperature stability, more than the number of days. A tub that lives on the fridge door — the warmest spot, and the one that swings closest to room temperature every time the door opens — has a shorter real life than the identical tub kept on a middle shelf toward the back, even if both carry the same printed date.

What touches the surface. A clean spoon, used once and never dipped back into anything else, does far less damage than a spoon that went from a plate of something else straight back into the tub. Sour cream is thick enough that contamination tends to stay localised near the surface rather than mixing straight through, which is part of why a thin layer of visible mould on top does not mean the whole tub is compromised in the same way a cloudy liquid would be — though it is still the point to stop, not to scrape off and continue.

How well it is resealed. The original tub lid, pressed back down flat, does a reasonable job. A container left loosely covered, or one that has been scooped from with the lid off and set aside "for a minute," lets in more air and more of whatever is floating around the fridge than it needs to.

Separation is normal. These things are not.

A thin layer of watery liquid pooling on top after a few days in the fridge is whey separating out, which is completely ordinary for a cultured product and not a sign of anything wrong — stir it back in. What is worth paying attention to is different from that:

• Smell. Sour cream is supposed to smell tangy and slightly acidic — that is the culture, not a warning. What is not normal is a sharp, distinctly unpleasant or ammonia-like smell layered on top of the usual tang. That shift is the most reliable single signal.
• Look. Beyond the normal watery separation, watch for yellowing at the edges, a change from smooth to grainy or lumpy throughout, or any mould — fuzzy spots in blue, green, black or pink. Mould on a thick, cultured product like this is a reason to discard it, not scrape around it.
• Texture and taste. If smell and appearance both check out, a small taste is a reasonable last step. A sharper, almost fizzy or bitter edge beyond the usual tang is the product telling you it has moved past its normal fermentation and into a different, less predictable one.

The false-negative case worth knowing about is the same one that applies to most dairy: a tub that had a warm stretch — left out during a long dinner, or riding home in a hot car — can be further along than its smell alone suggests, so a tub with a known warm patch in its recent history deserves a bit more scepticism than the calendar does.

The thing that actually helps

The printed date answers a question about the sealed tub sitting on a shelf in a shop. It has nothing to say about a tub that has been opened, scooped from a dozen times with three different spoons, and pushed to the back behind the jam. What actually matters at the moment you are deciding whether to use it is a much smaller question: when did this get opened, and has it been kept cold and covered since. Munch tracks that separately from the date on the label — marking an item opened starts its own countdown from that day, visible to everyone in the household, so the answer to "is this still good" does not depend on anyone remembering which Tuesday the tub was first opened.