21 CFR §137.220

1. (a)Durum flour is the food prepared by grinding and bolting cleaned durum wheat. When tested for granulation as prescribed in § 137.105(c)(4), not less than 98 percent of such flour passes through the No. 70 sieve. It is freed from bran coat, or bran coat and germ, to such extent that the percent of ash therein, calculated to a moisture-free basis, is not more than 1.5 percent. Its moisture content is not more than 15 percent.
2. (b)For the purpose of this section, ash, moisture, and granulation are determined by the methods prescribed in § 137.105(c).