Is it best to boil or simmer

A.� Boiling as a cooking technique works by heating food with liquid convection streams. Since this means cooking at a maximum temperature of 100C, it precludes browning as caramelisation requires a much higher temperature. This is why we sear and fry things before stewing or braising them if the flavour and cosmetic benefits of browning are desired.

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Boiling is a very efficient cooking process, because the whole surface of the food is in direct contact with hot liquid, delivering a rapid and effective transfer of heat from one to the other.

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There are very few things we actually want to boil because the extreme agitation of the bubbles can damage the food being cooked. For example, if you boil poultry or meat with bones, the tumbling effect causes gluey proteins to be extruded from the bones, which affect both the taste and appearance, but which creates great jellied stock and soup bases.�Pasta and green vegetables, on the other hand, benefit from the briefest cooking time in fast-boiling water.

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Q.� What's the difference between simmering and boiling and poaching

A.� Poaching or simmering is the gentle application of wet heat that ultimately delivers some of the great dishes of the world. A thermometre reading of 80-90C is about the right temperature for immersed meat, fish or poultry. The French make some enchanting distinctions here: a daube does not simmer, it murmurs (mijoter), while a slow-cooked stock trembles (fremir).

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Cooking in liquid is an excellent way of tenderising tougher, gelatinous cuts of meat. It is also a good way of instilling flavours into what is being cooked.

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Q.� How can you get your water hotter than 100C

A.� The only way is to put a lid on the saucepan. The weight of air pressing down on the water means that more energy is needed before molecules can vaporise from the surface. In other words, the water boils at a higher temperature - this is the work of a pressure cooker. As you increase the pressure on the surface of the water, you will raise the temperature at which it boils.

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By Katharine MacColl

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