What is starch? It’s what people sometimes add when they wash shirts and it is an ingredient in many medicines. But it’s also an important food!
Plants make starch from sugar molecules in order to store food for winter. Plants also use starch to feed seedlings or new sprouts. The starch is stored in the seeds of corn and wheat, in the stem in sorghum (a grain similar to Indian corn), and in the roots or tuber (underground stem) of yams and potatoes.
How do we know potatoes have starch?
Things Required:
Potato (peeled)
Strainer or cheesecloth
Aluminium foil
A paper towel
1/2 teaspoonful of flour
A grater
A bowl
A drop or two of tincture of iodine
1/2 teaspoonful of salt
Directions:
Grate a tablespoonful or two of potato into a bowl. Squeeze the potato mush through cheesecloth or a fine strainer onto a piece of aluminium foil. Pat the mush dry with a paper towel. Then apply a drop of iodine to it.
Place the salt and the flour on the aluminium foil. Apply a drop of iodine to each.
This Is What Happens:
The salt takes on the light brown tint of the iodine. The potato and the flour turn blue-black.
Science Behind It:
The blue-black colour tells us that starch is present. A chemical change takes place as the iodine combines with the starch. Starch is a carbohydrate, made up of carbon, hydrogen and oxygen.
In the supermarket, you may see packages labelled “potato starch”. Inside is a white, powdery substance ground from potatoes by machines. Huge screens filter out the potato fibre, and the potato starch is then left to dry in large vats.
Potato starch is used to thicken sauces and gravy and to replace wheat flour in cakes, if you don’t want to eat wheat.
