How long do opened olives last in the fridge?

An opened jar of olives in brine, kept in the fridge and topped up with its own liquid rather than left to sit half-dry above it, is usually fine for several weeks — closer to a month than to a week. Olives scooped loose from a deli case behave nothing like that, and are much closer to a fresh food with a countdown measured in days. Both are sold under the same word, "olives," which is exactly why a jar that has sat in the fridge door for a while is hard to judge without knowing which of the two you actually have.

Why brine buys so much more time than most opened food

Jarred olives are already a preserved food before the lid is ever opened. The brine they sit in is salty and usually acidic — vinegar in most commercial jars, or the olives' own lactic fermentation in a traditionally cured batch — and that combination is hostile to most of the organisms that spoil food, for the same underlying reason a jar of pickles or a bottle of vinegar resists them. Opening the jar does not switch that off. What it does is let air in and let a spoon in, and from that point on the olives keep as long as they stay genuinely submerged in the liquid that was protecting them, not sitting exposed above it.

Store-bought jar versus the deli counter

A sealed, pasteurised jar from a supermarket shelf is built to be shelf-stable for a long time unopened, and the brine inside is concentrated enough that "several weeks, refrigerated" is a reasonable, conservative expectation once it is open — many jars carry their own "refrigerate after opening, use within X weeks" line, and that number is the one worth trusting over a general rule.

Olives scooped from an open deli case are a different product wearing the same name. They are usually not pasteurised the same way, they have often been handled by tongs that dozens of other people used before you, and the oil or light brine many are dressed in is not doing the same heavy-duty preserving job as a proper jar brine. Treat a deli-case tub the way you would treat an opened dip: days, not weeks, and toward the shorter end if it is dressed in oil with fresh herbs or garlic rather than a simple, salty, vinegar-forward brine.

What actually decides how long a jar lasts, once it is open

Staying under the liquid. Olives sitting proud above the brine line dry out, discolour, and lose the protection the liquid was giving them. If the level has dropped after a few servings, topping it up with a little extra brine, or a light salted vinegar solution, keeps the ones near the top as protected as the ones at the bottom.

The utensil, not the fingers. A clean fork or spoon that never touches anything else adds far less to the jar than a hand reaching in, the same principle that applies to a tub of hummus or a jar of mayonnaise. It is a small habit that buys real time.

Oil-packed and marinated varieties. Olives dressed in olive oil with garlic, citrus peel or fresh herbs added — a common deli and farmers'-market style — are the exception to "brine keeps forever." Oil on its own is not acidic and is not the same protective barrier as brine, and fresh garlic or herbs sitting in oil at fridge temperature is exactly the kind of thing conservative food-safety guidance treats with more caution than a plain salty jar. Keep these refrigerated at all times and lean toward the shorter end of any "use by" guidance on the container.

Temperature. As with everything else living in the fridge door, the door itself is the warmest, least stable shelf in the fridge. A jar that gets moved to a middle shelf holds its condition better than one that rides the door through every opening of the day.

The one sign that actually means the jar is done

Vinegar can grow a harmless, cobweb-like "mother" that looks alarming but is not a reason to throw the bottle out. Olive brine does not get the same pass. Brine that has turned cloudy, slimy, or noticeably ropy — rather than just naturally a little murky from the olives themselves — is a sign that something is actually growing in it, and that is a discard signal, not a cosmetic one. The same goes for any fuzzy spot, any smell that has gone sharply off rather than staying briny and slightly fermented, or olives that have gone soft and mushy rather than staying firm. None of that is the same story as vinegar's harmless strands, even though the two can look similar at first glance in a jar on the same shelf.

Can you freeze them?

Not usefully for eating whole. Olives are mostly water held inside a firm structure, and freezing ruptures that structure the same way it does with cucumbers — thawed olives come out soft, mushy and watery rather than firm. If a jar genuinely will not get finished, freezing what is left works better as a step toward a cooked sauce, a tapenade, or something blended, rather than a plan to eat them straight from the jar later.

Olives are a natural fit for the part of the fridge nobody checks often — a half-full jar wedged behind the mustard, easy to forget precisely because it lasts long enough to stop feeling urgent. Munch tracks opened items by the day you actually opened them rather than the date printed on the lid, and shares that with everyone in the household who cooks, so a jar that has quietly been fine for three weeks does not get treated as a mystery, and a jar that has actually turned does not get missed either.