Why do we use iodine to test for starch?

1 Answer
MeneerNask
Jul 5, 2017

Because iodine in combination with starch forms an easy to see dark blue complex.

Explanation:

This reaction is very specific for starch + iodine. The complex is not heat-resistant, so it's not suited for testing hot starch solutions.

It's commonly used in (amateur) beer brewing to see if the mashing process (where grain starch is being converted to grain sugars) has completed. Iodine will not react with sugars, only with starch.

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