Holding a liquid just below the boil, where it cooks steadily without the violence that would tear delicate things apart.
Technique at a glance
A compact visual model of the lesson. Use the full mechanism and success criteria below when you practice.
Concept
Holding a liquid just below the boil, where it cooks steadily without the violence that would tear delicate things apart.
What changes
Water boils at 100°C and cannot get hotter at normal pressure, so a rolling boil is not hotter than a simmer by more than a few degrees — around 85-96°C against 100°C.
What good looks like
Bubbles rise lazily from one or two points on the base and break gently at the surface — not a rolling motion across the whole pan.
Practice counts when you cook
Reading this brief does not change your School state. Finish a real practice dish in Cook mode and log the cook; that cook is the evidence that advances the skill.
What to focus on
Mechanism
Water boils at 100°C and cannot get hotter at normal pressure, so a rolling boil is not hotter than a simmer by more than a few degrees — around 85-96°C against 100°C. The difference is not temperature but agitation. A boil is thousands of collapsing bubbles delivering mechanical energy, which shreds fish, clouds a stock by emulsifying fat and driving protein scum back into suspension, and breaks the emulsions in cream sauces. A simmer delivers the same heat without the turbulence. This is why almost everything long-cooked wants a simmer: the extra few degrees buy almost nothing and the agitation costs a great deal. The exceptions are when you specifically want that energy — reducing fast, or gelatinising starch in a slurry, which genuinely needs to reach a boil to thicken fully.
Success criteria
Bubbles rise lazily from one or two points on the base and break gently at the surface — not a rolling motion across the whole pan.
The surface trembles more than it moves.
A stock stays clear. Cloudiness is the reliable sign it has been boiling, not simmering.
Adjusting to a true low simmer usually means a lower flame than feels right, and often a lid set slightly ajar.
Failure guards
Stock is cloudy and greasy.
Boiled. Agitation emulsifies fat into the liquid and breaks up the protein scum that would otherwise be skimmed off.
Fish or dumplings fell apart.
Too vigorous. Delicate proteins need heat without mechanical force; poaching temperature is lower still.
A cream or egg sauce split.
Reached a boil. Emulsions and coagulating proteins both fail at the top of the range.