Kitchen chemistry: Recipes that teach

Reena Kurien

Cooking involves a series of chemical reactions. Knowing a bit of this chemistry will help you understand what takes place and why sometimes our cooking goes wrong.

Almost everything that we do in our daily life involves chemistry. It’s not just restricted to chemicals in laboratories. Cooking is essentially chemical reactions. Cooking is not just knowing how to combine the right ingredients but also understanding the reactions that take place due to changes in temperature and pH differences. This article talks about ‘why’ and ‘how’ chemistry works in the kitchen the way it does. It deals with visible changes in relation to colour, texture, consistency, and flavour.

The characteristic colour of fruits and vegetables is a result of the presence of one or more distinct chemical compounds. Green is produced by chlorophyll, the reds and blues by anthocyanin, yellow and orange by carotenoids, and certain creamy whites by flavones and flavanols. On cooking, colour changes occur and this is controlled by their solubility, the pH differences of the cooking medium and the duration of cooking.

Green beans
Plunging beans into boiling water causes the cells to pop and this results in a bright green colour. Longer cooking causes the cell walls to shrink and release an acid. Chlorophyll reacts with acids to give an unappetizing olive green substance called pheophytin, in which the magnesium of the chlorophyll is replaced by hydrogen. This can be overcome by cooking the beans in an open pan. The volatile acids present are allowed to escape and not condense back into the cooking medium. Addition of soda produces a bright intense green colour, but it is not advisable as it softens the cellulose rapidly, the vegetable becomes mushy and slimy. Some of the vitamins are also destroyed.

The author is a teacher at Vidyaranya High school, Hyderabad, where she has been teaching since 1981. She can be reached at [email protected].

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