Corn starch is a fine, silken powder milled from the dried seed cobs of corn. The plant itself has a long stem, growing up to five feet and flowering in early summer. 

Why we use it ?

We use corn starch to slow down the reaction between citric acid and baking soda. By binding to the baking soda as well as the citric acid, the cornstarch slows down the rate at which both of them dissolve.