Failure Rescue / Sauce & emulsion

Mayonnaise won't thicken or split — how to bring it together (and the raw-egg rule)

Broken mayo almost always comes back if you whisk it, slowly, into a fresh yolk or a spoon of made mayonnaise. First, the raw-egg safety note.

Do this now

Safety first — this is raw egg: if it (or the eggs) has been at room temperature for more than about two hours, or anyone eating is pregnant, an infant, over 65, or immunocompromised (and it isn't made with pasteurised eggs), do not rescue it — discard it and start fresh with cold eggs. If it is safe to save: put a fresh egg yolk (or a tablespoon of already-made mayonnaise) in a clean bowl, and whisk the broken mixture into it a teaspoon at a time. Rebuilt on a new emulsifier, it thickens within a minute.

Food-safety note — please read before fixing

Homemade mayonnaise is raw egg yolk. Pregnant people, infants, adults over 65, and anyone immunocompromised should not eat it unless it is made with pasteurised eggs. For everyone: use the freshest eggs, keep it refrigerated, use it within about three days, and never leave it at room temperature for more than two hours. The vinegar or lemon juice sharpens flavour and slows spoilage a little — it is not a substitute for cooking and does not make the egg safe for at-risk groups.

Why it happened

Mayonnaise is a lot of oil emulsified into a little egg yolk. It breaks when the oil goes in faster than the yolk can take it — the droplets get too big and the whole thing turns to soup. It also refuses to start when the yolk and oil are at very different temperatures (fridge-cold yolk, warm oil), which keeps the first droplets from forming at all.

How to fix it

Stop adding oil. Set the broken mixture aside — you will drip it back in, not throw it away.
In a clean bowl, start a fresh base: one egg yolk, or a tablespoon of made mayonnaise, or a teaspoon of mustard (mustard is a strong emulsifier).
Whisk the broken mixture into that base a teaspoon at a time at first, waiting until each addition is absorbed before the next.
Once it visibly thickens, add the rest in a slow, thin stream, whisking constantly.
If it is thicker than you want, loosen it with a few drops of water, lemon juice, or vinegar.

When to start over

The emulsion itself is almost always recoverable. What is not recoverable is time and temperature: if the mayonnaise (or the eggs before it) has sat warm for more than two hours, do not rescue it — the risk is bacterial, not textural. Discard and start with cold, fresh eggs.

What to watch for next time

Bring the yolk and oil to the same coolish room temperature before you start.
Add the oil painfully slowly at first — literally drop by drop until the base has thickened, then in a thin thread.
Watch for the mixture turning pale, opaque, and thick enough to hold a line from the whisk — that is the emulsion caught; only then is it safe to speed up.

How Terumi Morita thinks about it

Mayonnaise is the emulsion everyone should make by hand once, because it teaches the whole family of them: go slow until the base catches, then you can relax. But it is also the one where I am strictest about safety, because it never sees heat. Make it cold, keep it cold, eat it soon — and if anyone at the table is pregnant or vulnerable, reach for pasteurised eggs or a jar without apology.