Mayonnaise
The same ingredients, the same amounts, the same temperature — and a different result if you change the order. Pour the oil in at once and there is no sauce; add it drop by drop and there is. The first scenario where the engine answers "when" rather than "what".
Change them and see
Thick and glossy
The classic band. The oil droplets are packed so tightly they cannot slide past one another, and that crowding rather than any thickener is where the thickness comes from.
In order, minute by minute
Not a list of steps but a timeline: each one carries the minute it happens at and the temperature it happens at. Changing the order changes the result, and this shape is why the engine can say so.
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0 minutes
Bring everything to room temperature.
Cold oil is more viscous, and whisking cannot break it into small enough droplets. Large droplets mean an unstable emulsion. This step looks skippable and is behind a good share of failures.
What to look for The egg should not feel cold in the hand.
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30 minutes
Whisk the yolk, the salt and HALF the lemon juice.
Acid makes the lecithin more surface-active and thins the yolk a little, and both help it take the oil. Half the lemon is held back because it is what you use to loosen the sauce once it has thickened.
What to look for The yolk lightens and foams slightly.
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31 minutesCritical point
Add the oil DROP BY DROP. The first fifty millilitres decide everything.
Building an emulsion means wrapping every oil droplet in lecithin. Oil poured fast gathers into droplets too large to break up before the lecithin can reach them, and they never divide again. Once the sauce has thickened you can pour in a thin stream, because by then there is enough surface to do the dividing.
What to look for The sauce visibly thickens and pales. Until that happens, do not speed up.
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35 minutes
Add the remaining lemon to adjust it.
An over-thick mayonnaise has too little water phase; lemon or a spoonful of water opens it again. Oil thickens and water thins, and both are ends of the same emulsion.
What to look for It should fall slowly off a spoon and hold a peak.
The numbers that decide it
Thick and glossy
Read off the oil-to-yolk ratio. The thickness comes from how crowded the droplets are, not from any thickener.
15
The lemon is flavour and function at once: it makes the lecithin more effective and keeps the emulsion stable.
A built emulsion scatters light and looks satin. A broken one goes dull and the oil separates out.
What is happening in the pot
- ideal 0.8–1.5% Salt · 0.99% Right in the window. Flavours sharpen, bitterness retreats, water is held. Held in the system
What happened, why, and what to do
Some of these can be saved and some cannot. Writing up the second kind as though it were the first costs somebody another twenty minutes.
01 It never thickened ⌄
Why
The oil went in too fast at the start and the emulsion never formed.
Can be saved
Crack a fresh yolk into a clean bowl and add the broken mixture to it drop by drop. This works almost every time.
02 It thickened and then broke ⌄
Why
The yolk ran out of capacity: there was no lecithin left to keep the droplets apart.
Can be saved
Rebuild it into a fresh yolk drop by drop. Or whisk in a spoonful of hot water: increasing the water phase is sometimes enough.
03 Too thick, almost a paste ⌄
Why
The water phase has fallen too far behind the oil.
Can be saved
Whisk in a teaspoon of water or lemon. It opens at once.
04 Made with raw egg and meant to keep ⌄
Why
Mayonnaise is never cooked. Raw egg carries a salmonella risk, and an emulsion is a hospitable place for bacteria even in a fridge.
Cannot be saved
Not a rescue but a precaution: use pasteurised egg, keep it refrigerated and finish it within three days. Do not serve raw-egg mayonnaise to anyone pregnant, to infants, to the elderly or to anyone immunosuppressed.
Watch out Raw or lightly cooked egg carries a salmonella risk. Use pasteurised egg for mayonnaise, tiramisu and the like, and do not serve raw egg to anyone pregnant, to infants, to the elderly or to anyone immunosuppressed.
The safety check does not know the following. That is not the same as nothing being wrong — it means nobody looked, and anything meant to keep at room temperature has to be measured rather than assumed.
- Water activity
This is a model estimate rather than a measurement. How far each threshold behind it has been checked is below; fourteen of the fifteen still have no source on file, and saying so is better than not.
engine 1.0.0 · ruleset 2026.09.1 · confidence medium
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