Although the increase in boiling point due to adding even quite large amounts of salts is much smaller than the effect of altitude, salts can have quite different effects on the food that is being cooked – for example, if divalent salts (such as magnesium or calcium) are present they can affect the colour of green vegetables – making them appear a brighter green after cooking – as they interact with chlorophyll molecules to change their shape and hence their vibrational spectra.Ī trained scientist will readily understand these issues and be able to adapt their cooking to accommodate the water quality and the altitude. We do not cook with pure distilled water, but rather with the local tap or spring water the concentration and types of salts present in the water also affect the boiling point. But is it? We teach our children that water boils at 100☌, but it is only much later when those who progress on to higher levels of education begin to learn that the boiling point of water is not fixed, but actually quite variable – for example, in Denver, Colorado, which is about 1.6 km above sea level and where the atmospheric pressure is around 85 kPa, water boils at around 94☌.īut there is a further problem – water is not itself consistent from place to place. This can provide a system which is sufficiently reproducible that the same recipes can be used by cooks around the world and ensure they get similar results. Common practice when cooking vegetables, for example, is therefore simply to put them in boiling water for a fixed time. Without the use of expensive scientific equipment the only easy way is to use a phase transition that occurs at a fixed temperature – and the simplest and most accessible of these is to use boiling water. To ensure some degree of consistency between cooks there is a need to have some assurance that the temperatures used in different kitchens are closely similar (if not the same). One of the most basic kitchen operations is to heat food to change its texture or chemical make-up (or both).
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