Reading the surface
The only reliable way to judge this is by eye, and it is worth learning properly.
- Poach, 70–85°C
- Surface shivers. Occasional bubbles rise and disappear before the top.
- Bare or gentle simmer, 85–90°C
- Small bubbles break the surface in one or two places, every second or so.
- Simmer, 90–95°C
- Bubbles across the surface, steadily, but the liquid is not rolling.
- Rolling boil, 100°C
- The whole surface churns. Fine for pasta and green vegetables; wrong for almost everything else.
- A practical trick
- Most hobs cannot hold a simmer at their lowest setting on a large ring. Use a smaller ring, a heat diffuser, or set the pan slightly off-centre.
Why boiling ruins things
Three separate damages, and they apply to different dishes.
It emulsifies fat into the liquid, which is why a boiled stock turns cloudy and greasy while a simmered one stays clear. Once emulsified it cannot be skimmed off.
It agitates. Solids knock against each other and disintegrate, which turns a stew into a mush and breaks up fish and dumplings.
It tightens protein. Meat fibres contract harder and squeeze out more moisture at 100°C than at 90°C, which is why a boiled stew comes out dry and stringy even though it sat in liquid for hours.
The exceptions are dishes where agitation is wanted: pasta, green vegetables, and any reduction you want to happen fast.
Which dishes want which
- Stock — bare simmer, never boiled. This is the difference between clear and cloudy, and there is no way back.
- Stews and braises — bare simmer. In the oven if possible, which holds it steadily.
- Soups — gentle simmer, and only until the vegetables are done.
- Beans and pulses — gentle simmer. A boil breaks the skins and turns them to mush.
- Rice — a bare simmer with a lid, or the water boils away before the grain has absorbed it.
- Custards and anything with egg or dairy — below a simmer. They curdle.
- Pasta and green vegetables — a rolling boil. Here the movement helps.
- Reductions — a lively simmer to a boil. You want evaporation, and there is nothing delicate to damage.
Getting a stock right
The dish where simmering matters most.
- Start the bones or vegetables in cold water. Coming up slowly extracts more and keeps the liquid clearer.
- Bring it to the barest boil and immediately reduce the heat.
- Skim the grey foam off the surface as it rises, in the first twenty minutes. That is coagulated protein and it is what clouds a stock.
- Hold it at a bare simmer — a bubble every second or two — for as long as the recipe wants. Never let it boil again.
- Do not stir. Stirring breaks up solids and clouds it.
- Strain gently through a fine sieve or muslin, without pressing the solids, which forces particles through.
- Cool it quickly and refrigerate. The fat sets on top and lifts off cleanly.
Common questions
Why is my stock cloudy?
It boiled. Fat and protein have emulsified into the liquid and cannot be removed. It will still taste fine.
My hob will not go low enough. What can I do?
Move the pan to a smaller ring, use a heat diffuser, put the lid partly on, or move the whole thing to a low oven, which is the most reliable answer.
Does a lid change the temperature?
Yes — a lid traps heat and steam and will push a simmer towards a boil. Partly covered is often the right setting.
Is a "gentle boil" a thing?
It is a phrase people use for a lively simmer. If a recipe says it, aim for steady bubbles across the surface without churning.