The present study addresses an aspect of genotype by environmental influences on cereal grain quality that has not been researched extensively. The susceptibility of raw and cooked starch to enzymic hydrolysis has been examined using a set of well‐characterized wheat endosperm starch samples obtained from five wheat varieties grown in four different locations in 2 years. Native starch granules were hydrolyzed slowly, with genotype contributing most of variance between the samples during the initial stages of hydrolysis. Surface properties of the granules influenced the initial stages of hydrolysis. Environmental factors became increasingly influential as hydrolysis progressed, accounting for almost 50% of variance at 24 h, when 70–80% of the starch had been hydrolyzed. Of the environmental conditions associated with growing locations, temperatures before flowering and during grain filling were identified as contributing to variability in the susceptibility of native starch to enzyme hydrolysis. Cooked starch was hydrolyzed much more rapidly than native granules, with 80% of starch breakdown occurring within 90 min. For cooked starch, genotype contributed about 60–70% of the variance in the amount of starch hydrolyzed within 30 min and in the amount of starch remaining after 2 h. The strong genetic influence on the susceptibility of both native and cooked wheat starch to enzymic hydrolysis indicates the heritability of these characters.