Egg doneness and yolk texture, explained

Egg whites and yolks set at different temperatures, and that gap is what makes a soft boiled egg possible. Whites begin firming around 144°F / 62°C and are fully set by 158°F / 70°C. Yolks start thickening around 149°F / 65°C and don’t fully firm until about 167°F / 75°C. Timing an egg is really about deciding how far into the yolk that heat travels.

Why a runny yolk inside a set white is possible at all

It looks like it shouldn’t work. The white is on the outside, closer to the heat, yet it’s the part that ends up firm while the protected centre stays liquid — surely the inside should cook too, given enough time?

It does, eventually. What buys you the window is two things working together.

First, the proteins set at different temperatures. Egg white is mostly ovotransferrin and ovalbumin; ovotransferrin starts denaturing around 62°C, which is why a white turns opaque and jelly-like before it’s fully firm. Yolk proteins hold out longer, thickening from about 65°C and not becoming fully solid until around 75°C.

Second, heat takes time to travel. An egg is a poor conductor. Heat arrives at the shell instantly and works inward, so at any moment there’s a temperature gradient from the surface to the centre. Pull the egg at six minutes and the outer white has been past 70°C for a while, the inner white is just there, and the yolk centre hasn’t reached 65°C at all.

Boiling an egg is therefore not “cooking it for N minutes.” It’s choosing where to stop a heat wave travelling inward.

What each stage looks like

Notice how uneven the spacing is. There’s a full minute between very soft and soft, then only 45 seconds to jammy, then 75 seconds to medium, then three minutes to hard. That isn’t arbitrary — it reflects how fast the yolk’s temperature is changing at each stage. The middle of the range is where small timing errors show up most, which is exactly why the timer exists.

The 45 seconds between jammy and medium

The narrowest and most consequential gap on the chart. At 6:45 the yolk centre has just crossed into the thickening range — set enough to hold shape when you halve the egg, still soft enough to smear. By 8:00 that centre has spent another 75 seconds climbing, and the texture has gone fudgy: still moist, no longer spreadable.

Both are good eggs. But if you wanted jammy and got medium, the usual culprit isn’t your timing — it’s the missing ice bath. A hot egg out of the water keeps conducting heat inward, and carryover cooking alone can move you a full stage.

Why the ice bath is part of the recipe

This is the part most instructions treat as optional and shouldn’t. When you lift an egg out at 6:45, the outer layers are well above the yolk’s setting temperature, and that heat continues travelling inward whether or not the egg is in water. It doesn’t stop until the egg cools.

Left on the counter, a jammy egg keeps cooking for several minutes — enough to arrive at medium by the time you peel it. Ice water halts the gradient immediately. That’s why every time on this site assumes an ice bath: without it, the numbers mean something different.

The grey-green ring, and what it tells you

Push past about 12 minutes and sulfur compounds in the white react with iron in the yolk to form iron sulfide, which shows up as a grey-green ring at the boundary. It’s harmless, but it’s a reliable signal of two things: too long, and cooled too slowly.

It’s genuinely useful feedback. A ring means you have room to pull your hard boiled eggs earlier, or to get them into ice faster, or both.

Why sous vide behaves completely differently

A boiled egg has a temperature gradient — the outside is always hotter than the centre. Sous vide removes the gradient entirely: hold an egg at exactly 63°C for 45 minutes and eventually the whole egg is 63°C, throughout.

That produces a texture boiling can’t. The yolk is uniformly custardy from edge to centre, and the white stays very soft, because 63°C is enough to thicken yolk but not to fully firm ovalbumin. It’s the same physics read from the other end: boiling sets texture with time, sous vide sets it with temperature.

What changes the outcome besides time

• Egg size — about 30 seconds a step. A bigger egg means further for the heat to travel.
• Starting temperature — a room-temperature egg starts closer to its destination, so it needs about a minute less.
• Altitude — above 3,000 ft water boils below 212°F, so the whole gradient is cooler and everything takes longer. See boiling eggs at altitude.
• Method — steam transfers heat less efficiently than water, and dry air less still, which is why steamed and air fryer times run longer.
• A simmer instead of a boil — water at 190°F drives a cooler gradient, and every chart time runs short.

All of which the timer accounts for. Every one of them is really the same variable in disguise: how fast heat gets to the middle.