"Crude" is a chemistry term, not a quality judgment. The crude protein percentage is calculated by measuring total nitrogen (Kjeldahl method) and multiplying by 6.25 (the average nitrogen-to-protein ratio in animal tissue). The number includes any nitrogen source — true protein, free amino acids, and contaminants. The 2007 melamine pet food recall happened because melamine is nitrogen-rich and inflated apparent crude protein in adulterated formulas. Crude protein doesn't tell you about amino acid balance or bioavailability — a 30% crude-protein chicken-based food and a 30% crude-protein pea-protein-concentrate food are not equivalent.