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Sci Tech
QUESTION CORNER
Softness of chapathi
Chapathi, made of wheat, is soft when hot but becomes hard when cold. Why?
V. L. Narasimhan,
Hyderabad
Chapathis are made from a dough of wheat flour and water. The typical Indian chapati dough contains about 15 to 20 per cent water by weight. A lump of this dough is rolled to a thin (nearly) circular shape and is roasted to make a chapathi.
During this process of roasting the dough gets cooked inside and the contents of the dough undergo chemical changes. The wheat flour consists mainly of carbohydrates, starch, albumin and dietary fibres. The starch is a polysaccharide, essentially a polymer of glucose.
This undergoes hydration reaction when heated with water. The product of this reaction is dextrin, a gummy substance known as starch gum. This is a typical feature of flour made from all cereals like rice, wheat, ragi etc; when cooked with water, soft glue like substance forms. This becomes hard on drying.
The presence of a protein called gluten present in the wheat flour also forms a glue-like substance in the water-cooked chapathi. The wet gluey substances bind the fibre particles of the chapathi and render it soft.
Chapathis also lose substantial part of the water content slowly by the time they become cold. Specifically, the surface layers of the chapathis lose water faster and thus the glues set hard and the fibres bind to lumps of hard mass.
One usual method of retaining the softness of chapathis is to wrap the freshly prepared chapathis with a cloth. By this, the water content is not lost even when the chapathis are cold and renders them soft.
It is not the temperature of the chapathi that makes it hard; it is the loss of water that is responsible for the acquired hardness of the chapathis after some time of their preparation.
That is why they do not become soft if heated again. But if it is soaked in water or exposed to hot water vapour for a short while it resumes softness.
H. K. Sahu
Scientific Officer, IGCAR
Kalpakkam, Tamil Nadu
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