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The use of salt in cooking (1) The use of salt in cooking (2) By how much does salt increase the boiling point of water? Is all salt the same? "Low sodium” salt substitutes What affects the colour and texture of cooked vegetables? Should beans be cooked with the lid on or off? The chemistry of baking powder The structure of ice and water Why do pans stick? Enzymes and jellies The chemistry of flavour Chemical changes during cooking The science of ice cream ‘Asparagus pee’ How hot are chilli peppers?
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Learning objectives
• To devise and carry out experiments to test simple hypotheses.
• To develop the idea of the ‘fair test’.

Level
Age: 7–14.

Timing
One lesson of approximately one hour. Some of the planning could be done for homework.

Description
A discussion of why salt is added to water when cooking vegetables leads on to open-ended investigations devised by the students to discover (a) whether this salt can be detected in cooked beans and (b) what level of salt can be detected by taste.

Teaching notes
The lesson could be started by introducing Heston Blumenthal as a ‘scientific chef’ and showing the video clip of him discussing the use of salt in cooking food and/or by discussing some of the issues listed below at a level appropriate for the students concerned.

Index V01

Heston Blumenthal in the kitchen

Media: wmv(2) / wmv(15) / MPEG

One question posed by Heston Blumenthal early in his career as a ‘scientific chef’ was 'Why do cooks add salt (sodium chloride) when cooking vegetables, for example green beans?’ Possible reasons suggested by cooks included:

•
it keeps the beans green
•
it raises the boiling point of water so the beans cook faster
•
it prevents the beans going soggy
•
it improves the flavour.

A scientist colleague replied that there seemed to be no good reason because:

•
only the acidity and calcium content of the water affect the colour of the beans
•
adding salt does increase the boiling point of water but by such a small amount that it will make no difference to cooking times
•
vegetables will go soggy if cooked for too long whether salt is added or not
•
very little salt is actually absorbed onto the surface of a bean during cooking – typically 1/10 000 g of salt per bean which is too little to be tasted by most people.

Students can try to test some of these suggestions and explanations by experiment

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© RSC 2005