Eggs: Coagulation Temperatures and What They Decide

Two numbers

• Egg white begins to set at about 62°C.
• Yolk begins to set at about 68°C.
• Above 80°C the proteins contract hard and squeeze water out — dry curds sitting in liquid.

Nearly every egg failure follows from those three lines. Eggs go wrong from too much heat far more often than from too little.

Those two numbers are where setting begins. The order in which they finish is the reverse: white needs close to 80°C to set properly while yolk is done by about 70. So hold a whole egg at 68–70°C and only the yolk sets — that is Onsen tamago, the exact inverse of a soft-boiled egg's set white around a running yolk.

It also explains what the boiled-egg table below actually measures. That table is not measuring a temperature but a gradient — shell at 100°C, centre still cold — so it cooks outside-in. Remove the gradient and the sequence inverts.

When no heat is needed at all

The numbers above describe one route to a set egg. There is another. Above about pH 12 the same proteins unfold and re-link with no heat at all, so the white of a Century Egg becomes a translucent amber jelly over five weeks and never sees a flame. The network it forms is coarser, which is why that white ends up clear rather than opaque.

And a second route, which sets the other half of the egg

Cure the same duck egg in salt instead of alkali and it also comes out set with no heat — but nothing else about it matches. The Century Egg page states the pair outright: "the same egg cured in salt rather than alkali. Instead of going dark and creamy the yolk turns orange and hard." Alkali cuts the protein apart and sets the white, leaving the yolk dark and soft; brine pulls water out and leaves the white thin and salty while the yolk goes firm, grainy and orange. Two months, no flame either way, and opposite halves of the egg end up solid.

Which is why "whole eggs and yolks do not set to the same firmness", below, reads backwards here. That section is about heat: heated, the white is the part you can slice and the yolk stays creamy. Salt-cured, the yolk is the part you can slice — so Mooncake sets a whole one at the centre of its pastry and cuts straight through it, and Lo Mai Gai treats it as a solid ingredient dropped into a parcel rather than as an egg.

Scrambled eggs and omelettes want low heat

Put an Omelette over high heat and the outside browns and tightens while the inside goes dry. Tenderness only comes from low heat, slowly, kept moving.

• Medium-low pan: butter should sizzle without colouring.
• Take it off while it still looks slightly underdone. Residual heat keeps cooking it.
• A splash of milk or cream raises the setting temperature and widens your margin. Starch does the same thing on a much larger scale — granules swollen at 60–75°C get between the egg proteins and lift the setting temperature by tens of degrees. That is why the flour-bearing custard of Clafoutis goes into a bare 180°C oven with no water bath and does not curdle, and why the custard in an Egg Tart carries cornflour.

Gyeranmari applies the same principle in layers — each layer has to be rolled before it fully sets, or the layers will not bond.

When the sheet is a material rather than the dish

Everything above is written for an egg that is the dish, where the target is tenderness and the instruction is to stop while it still looks underset. A thin sheet cooked in order to be cut up wants the other end of the same range. Kerak Telor spreads a duck egg 5mm thick over rice and needs it to hold together as one sheet, because that sheet is the structure of the dish; Laksa shreds one over the noodles, the cha-om version of Kaeng Som cuts one into squares, Spam Musubi lays one between the meat and the rice, and Gimbap fries a thick one into long strips where Janchi-guksu fries a thin one. A knife on an underset sheet tears it, and a shred that will not hold an edge disappears into the bowl.

So what decides how far you take it is not how it will feel in the mouth but what happens to it after it leaves the pan. The heat stays low either way — browning is still a fault, since a browned sheet is tough and the colour is wrong in a garnish. What moves is the moment you stop.

Gyeranmari, just above, is the third answer and the most exacting, because it is neither: every layer has to be caught before it sets or the layers will not bond, so the roll is built entirely out of sheets that are underdone on purpose and finish in the stack. Omurice keeps two of the three answers on one plate — the classic wraps the rice in a sheet set firmly enough to lift, while the fuwatoro version lays a barely-set one over it and cuts it open to spill.

Boiled egg timings

Starting in cold water makes timing unrepeatable. Lower them into boiling water and time from there (fridge-cold, medium eggs):

• 6 min — white barely set, yolk still liquid.
• 7 min — jammy, set only at the yolk's edge.
• 9 min — just moist in the middle.
• 11 min — fully set, not yet chalky.
• 13 min+ — crumbly yolk with a grey-green ring (iron sulfide). Overcooked.

Into cold water immediately: it stops the carryover cooking and helps them peel.

Getting them to peel

Very fresh eggs peel badly — the internal pH is low and the white clings to the membrane. Eggs a few days old peel better. Beyond that, starting in boiling water and chilling hard afterwards does the most.

Steamed custards: ratio and a sieve

For Gyeranjjim, egg to liquid is about 1 : 1.5. Less and it is rubbery; more and it will not set.

Two things make the texture:

• Pass it through a sieve to catch the chalazae and any lumps — that is what makes it smooth.
• Low heat, lid on. Steamed hard it pits and weeps. Once the steam is up, drop the heat.

Yolk-thickened creams like Chocolate Mousse follow the same rule — past 70°C they curdle, which is why they are made over a water bath. See also Why sauces split.

Whole eggs and yolks do not set to the same firmness

There is something the two numbers do not say: how firmly each sets. White sets firm enough to slice; yolk sets soft and creamy.

So the same custard divides on what goes into it. Crème Caramel uses whole eggs and stands up when turned out of its mould; Crème Brûlée uses yolks alone and has to be spooned. Same milk, same sugar.

When there are two centres

Scotch Egg has two centres a centimetre apart wanting opposite things — sausagemeat near 70°C, yolk under 68. They cannot be hit at once, so it staggers them in time: boiled to 6:30 so the white is just firm enough to wrap, into cold water to stop the carryover, thirty minutes in the fridge, then fried.

Here "very fresh eggs peel badly", above, stops being an annoyance and becomes a constraint: a torn soft-boiled white leaves nothing to wrap. Tea Egg wants days-old eggs for the same reason, and there a torn white loses the whole pattern — the shell is kept on as a mask, and the colour enters only along the cracks.

Or one egg that has to finish in two states at once

A scotch egg has two different things wanting two temperatures. Oyakodon has one egg wanting two finishes: a set mesh underneath, holding the chicken and the sauce into something that will slide onto rice in one piece, and a loose layer on top that is still liquid and re-wets the rice. It cannot stagger in time the way a scotch egg does, because it is one material in one pan — so it staggers by dividing it. Two-thirds goes in and is covered until half-set; the last third is added with the heat already off. Katsudon does the same with half and half.

Gyudon takes the loose half to its limit by not cooking it in the pan at all — an onsen tamago dropped on top, where, as that page puts it, the loose white becomes the sauce.

The numbers at the top of this guide are what make the second addition work. The broth is already simmering, and above 80°C the proteins contract hard and squeeze water out. With the burner on, that line is very easy to cross; lid on, heat off, and thirty to sixty seconds of residual warmth is what keeps the last of the egg under it.

Keep fat away from whipped whites

A trace of yolk in the whites and they will not whip: the fat destabilises the protein film.

• The bowl and whisk must be grease-free.
• Room-temperature whites whip higher.
• Acid — a few drops of lemon or vinegar — stabilises the foam.
• Add the sugar gradually rather than all at once.

When the fat cannot be kept out

Every line above is a rule of exclusion — a clean bowl, no yolk — and it works because the recipes it was written for want the whites on their own. A recipe that wants the whole egg has no such option. Genoise is aerated by whipping whole eggs and nothing else, and it puts a number on the problem: a whole egg is "about a third yolk by weight", so the thing this section says will stop a foam is a third of the egg.

What answers that is not exclusion but temperature, and this guide already holds half of the answer. Room-temperature whites whip higher, above, is the same mechanism at a smaller setting: soft fat does less damage than firm fat. A genoise pushes it much further and warms the eggs and sugar over a water bath to 40-45°C before a whisk goes near them, and its own step says why — "The fat in the yolk gets into the bubble walls and bursts them; warmed, that fat is fully liquid and the proteins unfold faster, so a foam forms at all." The fat is still in there doing the same thing; it has simply stopped winning. Prinsesstårta performs exactly that step on the way to its sponge — "Warm the eggs and sugar over a water bath to 40°C, then whip on high for 8 minutes" — as a procedure, with no reason attached.

The bill is worth stating, because it is the same trade When the sheet is a material rather than the dish makes further up. A whole-egg foam, as the genoise page puts it, is "weaker than a meringue and steadier in exchange." And "the price of not being fluffy is that it survives being split into layers and brushed with syrup." Keeping the fat out buys height; tolerating it buys a foam that can be split into layers and soaked.

Between those there is room for other answers, and none of them contradicts the bullets above:

• Put the fat where the foam never meets it. Chiffon cake whisks the yolks with oil into a batter of their own and folds a clean meringue into that, so "The meringue does all the aerating", and the fat only ever meets a foam that is already built. Its page cites this guide for the clean bowl and then goes a step stricter, stopping at "peaks that droop" because "A stiff meringue cannot stretch further and tears as you fold."
• Fold the fat back in and beat the clock. The capeado of chile relleno is "a meringue with the yolks folded back in" — the exact thing the opening line of this section forbids — and it holds only because it goes straight into the oil. That page states the bill plainly: "That is why it is light, and why it collapses if it stands."

Where the whites really are kept clean, the reason is usually that nothing else is lifting the cake. Dobos torte carries no raising agent — "The meringue bubbles are the only lift, which makes folding non-negotiable." — and a macaron rests its shells on this section’s opening line restated: "fat collapses the foam outright". At the far end, pound cake whips no egg at all: it beats air into solid butter, "sugar crystals scraping the butter and cutting air pockets into it", so there the fat is the structure rather than the contaminant, and the recipe hangs on holding it at a temperature where it can do that job — "Butter outside 18-20°C nearly always fails."

That reversal is the other foam’s principle rather than this one’s, and it is worked out in dairy and heat, where the fat holds the foam up and cold is the requirement. What this section adds is the case sitting between the two: an egg whose fat cannot be removed, warmed until a foam forms anyway.

Dishes where the egg is the dish

Tamago Sando lives or dies on the texture of a hard-boiled egg, so the timing is the recipe; French Toast is a custard absorbed into bread, so the bread needs time to take it up.