Most mayonnaise failures are recoverable, and the fix is almost always the same one: give the fat a fresh surface to cling to. What differs is which failure is actually in front of you. A batch that never thickened needs a different read than one that thickened fine and split an hour later, and a jar that turned watery in the fridge overnight isn't broken the same way either. Only one of these is not worth trying to save.
It Never Thickened at All
If the bowl still looks like oily vinegar — thin, translucent, never once turning pale and thick — the yolk never got the chance to coat the oil before the droplets found each other again. This usually means the oil went in as a stream from the very first drop, before any emulsion existed to help carry the rest. The fix is a full restart: whisk a fresh yolk, or a teaspoon of water, alone in a clean bowl, then dribble the failed mixture back in the same slow way you'd add oil to a new batch. About a cup of that failed mixture per fresh yolk is the ratio to work from.
Grainy Isn't the Same as Broken
A mayonnaise that looks flecked or slightly curdled, but hasn't split into a visible pool of oil, is an earlier stage of the same problem. Droplets have started finding each other, but not enough of them have merged to collapse the whole batch. This one is the easiest catch. Stop pouring, whisk hard for a few seconds, and the texture usually smooths back out on its own — most of the surfactant is still doing its job, it just fell behind for a moment.
It Thickened, Then Split
This is the failure most people mean when they say mayonnaise "broke": it looked done, and then it didn't. Either the oil kept coming after the yolk's lecithin was already at capacity, or you pushed well past the working ratio of about a cup of oil per yolk, even with a careful hand. The fix is the same fresh-surface trick as a batch that never came together — a new yolk, whisked alone, taking the failed mixture back in slowly.
Thin Isn't Broken Either
A smooth mayonnaise that just won't get thick isn't a failed emulsion at all. It's an emulsion that never got enough oil relative to acid and water to reach full body. Nothing to rescue here — keep whisking in oil, a little at a time, until the ratio catches up to roughly a cup per yolk.
Why It Broke Overnight in the Fridge
Mayonnaise that separates after a night in the refrigerator, even though it was smooth going in, fails by a different mechanism entirely. Refrigerator temperatures, 35 to 40°F (2 to 4°C), are cold enough to partially solidify some of the oil into sharp-edged fat crystals, and those crystals can tear through the coating around a droplet the way a whisk never would. Bring the jar fully back to room temperature before judging it broken. Often the crystals melt, the film reseals itself, and a gentle whisk brings it right back — no fresh yolk required.
The One Failure That Doesn't Come Back
Every fix above assumes the yolk itself is still liquid raw egg, just poorly distributed. If instead you see actual solid curds — small, opaque, yellow lumps that don't dissolve no matter how hard you whisk — the yolk cooked. That happens with oil added too hot, or a food processor run long enough to heat the bowl. Cooked egg protein has permanently changed shape. It will not go back into an emulsion. That batch gets thrown out, not rescued.
How Long You Can Keep Troubleshooting It
Raw yolk sitting out while you work a stubborn batch back together is still raw yolk sitting in the range where bacteria multiply, 40 to 140°F (4 to 60°C). Treat two hours as a cumulative total on the counter, not two hours per attempt. If you've already spent that long trying to save one bowl, it stops being a texture problem — start over with a fresh yolk instead of continuing to work the same one.