How long does cold brew coffee last in the fridge?

The short version: black cold brew concentrate, kept sealed and cold, is usually fine for one to two weeks — noticeably longer than most people expect from something that lives in the fridge door. Diluted, ready-to-drink cold brew tends to hold up for three or four days once opened. Add milk, cream or a dairy creamer to any of it, though, and the jar is no longer running on coffee's clock. It's running on the dairy's, which is much shorter and does not care how patient the coffee underneath it is.

Why cold brew is unusually patient

Two things are working in its favour. First, it is brewed cold, which extracts less of the oil and compound profile that turns hot-brewed coffee stale and bitter within a day of sitting in a pot. Second, black cold brew is mostly water and dissolved coffee solids — low in the sugar, protein and free moisture that bacteria actually need to get going. It is not a sterile liquid, and it is not immune to anything, but it is a much less hospitable place for spoilage than a carton of milk sitting one shelf over. That is the reason cafés can hold a batch for well over a week without anyone getting sick, and why a jar you made on Sunday is a reasonable thing to still be drinking the following weekend.

What actually changes over that time is flavour, not safety

The dominant failure mode for black cold brew is not spoilage — it is oxidation. Every time air gets into the jar, a little more of the fresher, brighter flavour compounds break down, and what is left drifts toward flat and slightly bitter. This happens whether or not the coffee is "still good" in any safety sense, which is exactly why cold brew rewards a different kind of attention than milk does. Nobody needs to sniff a jar of week-old cold brew looking for sourness the way they would milk; the honest question is closer to "does this still taste like something," and that answer fades gradually rather than announcing itself.

The three things that actually decide the window

• Concentrate versus already diluted. Undiluted concentrate, stored airtight, is the longest-lived form — the coffee-to-water ratio is high enough that there is very little free water for anything to use. The moment you cut it with water or ice, you have created a weaker, wetter liquid that behaves less like concentrate and more like a regular beverage, and the shorter window applies from that point, not from when the concentrate was first brewed.
• Container and light. An airtight jar or bottle slows the oxidation that dulls the flavour; a loosely covered jug lets air keep working on it every time the fridge door moves. A dark bottle or an opaque container also helps, since light degrades coffee compounds faster than a dark fridge shelf does on its own.
• Whatever you added. Sugar syrup mixed in behaves roughly like the syrups covered elsewhere on this site — stable on its own, but no longer sterile once a used spoon has been in and out of the jar. Milk, cream or a dairy creamer changes the category entirely: from that point the jar is an opened dairy product with coffee in it, and it should be judged the way an opened carton of milk or cream is, not the way black cold brew is.

Store-bought cold brew plays by different rules

A bottle of cold brew from a shop or a carton from the supermarket was made and packaged under conditions a home kitchen does not replicate, and it carries its own printed date for exactly that reason. Once it is opened, the honest move is to follow the "use within X days of opening" line on the label rather than the general homemade-concentrate window above — the same logic that applies to an opened carton of milk. The maker knows what pasteurisation or filtration their product went through; a general rule does not.

How to tell staleness from the real thing

Staleness is the default outcome and is not a safety concern — it just tastes worse. Genuine spoilage is rarer in black cold brew but not impossible, and it looks different from a milk carton going off: a sour, fermented smell that is not just "flat coffee," visible mould on the surface (more likely once sugar or dairy has been added), or a fizzy, slightly carbonated quality to a liquid that should be still. Any of those is the point to stop, the same "when in doubt" rule that applies everywhere else on this site. Everything short of that is a flavour judgement, not a safety one, and it is fine to keep drinking a jar that has simply gone a bit flat.

The habit that actually helps

Write the brew date on the jar, the same trick that works for milk and for leftovers, because "I think I made this Sunday or was it the one before" is a much harder question to answer with a spoon in your hand than with a date already in front of you. In a shared fridge it matters even more: a jar of dark liquid with no label reads as either treasure or trash depending on who opens the fridge, and it is usually thrown out by whoever is less sure. The other habit worth keeping is separating a portion before adding milk — pour what you are drinking now into a cup and add the creamer there, rather than tipping milk into the whole batch. That keeps the rest of the jar running on coffee's slow clock instead of pulling the entire thing onto dairy's fast one.

None of this needs a shelf-life table memorised. It needs one date on the jar, a plain jar kept separate from whatever you added milk to, and the knowledge that with cold brew, "gone a bit flat" and "gone off" are usually two different questions with two different answers.