Starch agar consists of starch. The secretion of amylase enzyme by some microbes cause hydrolysis of starch around the colony. The plate flooded with iodine solution after incubation period. The amylase prodding colonies appear unstained and form a color zone because they’ve hydrolyzed starch. The colonies that don’t produce amylase, still have starch in their surrounding and appear dark-blue or black (color of starch-iodine complex) by reaction of starch with iodine. There is no clearance zone around the amylase-negative colonies. Thus, the media differentiates amylase producers from non-amylase produces and can be treated as a differential media. Solution Starch agar consists of starch. The secretion of amylase enzyme by some microbes cause hydrolysis of starch around the colony. The plate flooded with iodine solution after incubation period. The amylase prodding colonies appear unstained and form a color zone because they’ve hydrolyzed starch. The colonies that don’t produce amylase, still have starch in their surrounding and appear dark-blue or black (color of starch-iodine complex) by reaction of starch with iodine. There is no clearance zone around the amylase-negative colonies. Thus, the media differentiates amylase producers from non-amylase produces and can be treated as a differential media..