How long does opened tahini last in the fridge?

Short answer: an opened jar of tahini kept anywhere cool and sealed is realistically good for several months, whether or not it ever sees a fridge — closer to the timeline of peanut butter than to the five-to-seven-day window of an opened tub of hummus, even though the two sit next to each other in a lot of recipes. What throws people off is not spoilage at all. It is that a jar of tahini kept cold turns into something closer to a stiff paste or a solid block, which looks like something has gone wrong when nothing has.

Why tahini starts from the same low-risk place as peanut butter

Tahini is ground sesame seeds and their own oil, nothing else in most jars, and that composition matters more than anything printed on the label. Bacteria and mould need water to get going, and a paste that is mostly fat has very little of it to offer. This is the same underlying reason peanut butter sits safely in a cupboard rather than a fridge in most kitchens — an oily, low-moisture paste is simply an unfriendly place for the organisms that spoil fresh food. Hummus, by contrast, is blended with lemon juice, garlic and water, which puts it in the moist, close-to-neutral range that food-safety guidance treats far more cautiously. Tahini on its own never gets there.

So does it actually need the fridge?

Not for safety, in the way milk or a cut vegetable does. What the fridge is genuinely doing for a jar of tahini is the same job it does for a bottle of oil: slowing oxidation, the slow chemical drift that turns fresh sesame oil flat and eventually bitter over time. A jar kept in a cool, dark cupboard and used within a couple of months holds up fine at room temperature. A jar that will sit half-used for longer than that, or that lives somewhere warm — a kitchen that gets direct sun, or a cupboard near the stove — keeps its flavor noticeably longer in the fridge. Neither choice is wrong; the fridge just buys more time against a flavor problem, not a safety one.

Why a cold jar turns into a brick

This is the part that actually surprises people. Sesame oil has a fatty-acid makeup that thickens dramatically once it drops below room temperature, far more than most vegetable oils do, and a jar of tahini has no stabilizers in it to fight that the way some commercial peanut butter does. The result is a jar that goes from pourable to stiff, sometimes stiff enough that a spoon will not go in without effort, and the oil that was floating on top before refrigeration can separate out and re-set as a firmer layer once it is cold. None of that is the paste going bad. It is the same oil behaving differently at a lower temperature, the way olive oil turns cloudy and semi-solid in a cold fridge and goes clear again on the counter. Letting a chilled jar sit at room temperature for twenty or thirty minutes and stirring it firmly from the bottom up, scraping the sides as you go, brings it back to something spreadable again.

What tells you a jar is actually finished

The real end point for tahini is rancidity, not hardness, and the two do not feel the same. Rancid sesame oil smells and tastes distinctly off — sharper than fresh tahini's nutty, slightly bitter profile, sometimes described as smelling like old paint, crayons, or wet cardboard. That smell will not go away with stirring or warming, because it is a chemical change in the oil itself, not a texture one. A separate and much rarer failure is mould, which only shows up if moisture gets into the jar — a wet spoon dipped in and put back, most commonly — and looks like mould anywhere else: fuzzy spots on the surface, not just a firmer paste underneath. If a jar smells like sesame, even a slightly muted version of itself, it is fine. If it smells sharp or off, or has anything growing on the surface, it is not.

Getting the most out of a jar

• Stir before you store it, not just before you use it. A well-mixed jar separates less dramatically in the fridge than one that already had a thick layer of oil sitting on top when it went in.
• Store it upside down occasionally. Flipping a sealed jar every so often lets gravity redistribute the oil instead of letting it settle permanently at one end, which makes the next stir-through easier.
• Keep a dry spoon in it. The same rule that protects a jar of jam or a tub of hummus applies here — any water introduced into an otherwise dry, oily paste gives mould somewhere to start that it would not otherwise have.
• Reseal it tightly. A loosely closed lid lets in the air that oxidation runs on, which is the actual clock running on a jar of tahini, whether it lives in a cupboard or a fridge.

Tahini is also an easy jar to lose track of, since it gets used a spoonful at a time in things like hummus, dressings and marinades rather than eaten on its own, and a half-used jar can sit at the back of a shelf for months without anyone noticing whether it was opened last week or last spring. Munch tracks an opened jar with its own shorter countdown once you mark it opened, separate from the sealed date on the label, so the question of how long a specific jar has actually been open does not depend on remembering when you last reached for it.

The practical takeaway is close to the one for peanut butter or a bottle of oil: a stiff, cold jar of tahini is not a jar going bad, it is a jar behaving exactly the way its oil is supposed to at that temperature. The thing actually worth checking for, occasionally, is smell — sharp and off means finished, nutty and mild means it is exactly what it looks like, just cold.