This is a normal part of milk. The nonprotein nitrogen (NPN) fraction is composed of urea and other low molecular compounds such as creatine and creatinine. About 50% of the NPN in milk is urea, and variation in NPN is attributed primarily to variation in urea content. Nonprotein nitrogen has little nutritional value and does not contribute to cheese yield. Therefore, it does not have the same economic value as “true” milk protein to either the processor or the consumer.