Acid casein is precipitated by acidifying skim milk to the isoelectric point of casein, producing a product used primarily in food and industrial applications. Rennet casein is coagulated enzymatically and is preferred for cheese analog and processed cheese manufacture due to its superior meltability. Both fall under the same SITC heading, but buyers should specify the type in purchase contracts because functional properties, pricing, and end-use suitability differ significantly.

Food-grade casein must originate from dairy establishments that FDA has determined meet US food safety standards, either through equivalency agreements or facility-by-facility review. Importers must comply with FDA's Foreign Supplier Verification Program, ensure accurate labeling as a milk-derived allergen, and be prepared for port-of-entry sampling. Consulting a licensed customs broker with dairy import experience is strongly recommended given the complexity of admissibility review.