Evaporation

Evaporation is the process by which a liquid changes into vapour from its surface. In cooking, evaporation removes water from a liquid or food, which can concentrate flavour, increase viscosity and reduce volume. It is an important part of sauce reduction, stock making, jam preparation and many other techniques.

What affects evaporation?

• Surface area: a wide pan generally allows more liquid to evaporate than a narrow, deep pot.
• Temperature: higher heat usually increases the rate of evaporation, although the liquid and cooking method matter.
• Air movement: moving air can carry away water vapour and support evaporation.
• Humidity: surrounding humidity affects how readily water vapour leaves the surface.
• Covering: a lid traps vapour and reduces net evaporation compared with an uncovered pan.

Examples in the kitchen

Reducing a sauce concentrates flavour and body as water evaporates. Simmering stock uncovered reduces volume. Cooking fruit into jam removes moisture and changes the final consistency.

Chef’s tip: Use a pan with enough surface area and control the heat to achieve the desired reduction without scorching. Remember that salt and other dissolved ingredients become more concentrated as water is removed.

Key distinction: Evaporation removes liquid as vapour. Reduction is a culinary technique that deliberately uses evaporation to concentrate a liquid.