When cooking, what difference does it make if the water is simmering or boiling vigorously, given that water boils at 100 degrees?
Eric Kvaalen
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Les Essarts-le-Roi, France
It doesn鈥檛 matter, unless you are trying to evaporate a portion of the water. A rapid boil is a big waste of energy. In fact, it would be best to maintain the pot at 100掳C without any simmering. There are temperature probes that can be put in a pot and which control the heating, allowing energy expenditure to be reduced.
It is fortuitous that water boils at a temperature that allows food to be cooked. If it boiled at a lower temperature, we would have difficulty cooking food, and if it boiled at a higher one, food would easily get overcooked.
Tim Lewis
Narberth, Pembrokeshire, UK
I have never been able to persuade my partner that it takes just as long to cook vegetables whether they are boiling furiously or simmering. More energy is used and more steam is produced when boiling though. Cooking times by boiling can be shortened only by using a pressure cooker.
Greg Harris
Abu Dhabi, United Arab Emirates
For a chef, the difference between boiling and simmering is crucial. The strength of the boil affects the rate of reduction, important for producing water-based sauces, and is critical for avoiding the scorching of food at the bottom of the pot.
The 100掳C temperature limit cannot be exceeded under sea-level conditions, but a pressure cooker can be used to raise the boiling point. However, the cooking of everything from red sauce to pastries is complicated by altitude. My occasionally Colorado-based parents have often softened the delivery of a potentially below par meal with a caveat about the unreliability of our old recipies at 2172 metres up!
Martin Pitt
Leeds, UK
Vigorously boiling water heats food faster than static water does at the same temperature for the same reason that wind cools faster than static air at the same temperature.
In both cases, there is a layer of fluid/gas on the surface of the object that provides insulation. Movement reduces or strips off this layer. Boiling provides this motion, and the more vigorous, the greater the effect.
David Muir
Edinburgh, UK
If you put potatoes into boiling or simmering water, both at 100掳C, they will cook equally quickly as heat is conducted directly from the water to the vegetable. Any heat over that required to reach 100掳C converts liquid water to water vapour.
This heat is then lost to the room when the vapour condenses in the air to form steam or to produce condensation on cold surfaces, like windows.
It is a different kettle of fish if you are steaming vegetables that aren鈥檛 in direct contact with the boiling water. As water vapour condenses on the vegetables, they are cooked by the latent heat of evaporation when the vapour condenses on the vegetable.
In this case, the faster you boil the water, the more vapour that is produced and the greater the amount of condensation on the vegetables, cooking them faster. This also explains why a scald due to steam can be more severe than scalding from boiling water.
Guy Cox
Sydney, Australia
When water is actively boiling rather than simmering, we are putting more heat into the pan than is required to maintain its temperature.
鈥淎 rapid boil is a big waste of energy. It would be better to maintain the pot at 100掳C without any simmering at all鈥�
This means that when we put food items in, they will reach cooking temperature more rapidly, because the excess heat can transfer to the food. This stops food getting soggy and reduces cooking time a bit.
However, once the food reaches 100掳C, there will be no further impact on its cooking time, so it is usually better to reduce the heat so the water simmers. The exception is if the turbulence of a rapid boil would be useful to prevent items sticking together.
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