Idaho Code § 37-312
Butter is the product made by gathering the fat of fresh or ripened milk or cream into a mass, which also contains a small portion of other milk constituents, with or without salt or a harmless coloring matter. Butter shall be clean and non-rancid and shall contain not less than eighty percent (80%) of butterfat. Whey butter or whey cream butter is the food product made by gathering the fat of fresh or ripened whey cream separated from cheese whey and formed into a mass, which also contains a small portion of other milk constituents, with or without salt or a harmless coloring matter. Whey butter shall be clean and non-rancid and shall contain not less than eighty percent (80%) butterfat. The term butter includes whey butter and whey cream butter.
Idaho Code § 37-312