Olives

Unopened jarred or canned olives keep 1–2 years in the pantry. Once opened, refrigerate them — they keep about 12–18 months in the fridge in their brine.

Keep them submerged. Olives above the brine line oxidize, shrivel, and mold quickly, while submerged olives keep for the better part of a year. If the brine runs low, make more: roughly a teaspoon of salt per cup of water, or use a little olive oil to cover the surface.

Use a clean utensil, never fingers.

Deli-counter olives are usually a fresher, less heavily processed product and keep a shorter time — a few weeks — and should be kept in their liquid too.

Olives do not freeze well; they turn soft and mushy.

Raw olives are inedibly bitter because of a compound called oleuropein, and every olive you have ever eaten has been through a curing process to remove it — brine curing, lye curing, dry salt curing, or water curing. That process is also what preserves them.

The result is a food protected by salt and usually acid together, with a water activity low enough and a pH often low enough to make microbial growth difficult. This is why an opened jar keeps for the better part of a year while most opened refrigerated foods keep for days.

The brine is doing that work, which is why keeping the olives under it matters so much. An olive exposed to air loses the salt protection at its surface, oxidizes, and provides a landing site for mold.

A white film or cloudiness in olive brine is usually harmless — either yeast growth, which is common and expected in naturally cured olives, or precipitated salts. A thin white surface film can be skimmed off if the olives beneath smell and taste normal.

The signals that matter: a bulging lid or a jar that hisses on opening, fuzzy colored mold, brine that has gone slimy or ropy, a sharply fermented or foul smell, and olives that have gone soft and mushy rather than firm.