A method and app. for enzymic hydrolysis of proteins comprises a 1st vessel in which the substrate and enzyme is mixed and the substrate undergoes a 1st hydrolysis. This hydrolyzate is subjected to a 2nd hydrolysis step in a tube or tubes contg. stationary mixing elements. Using this method and app., peptide mixts. of well-defined compn. or degree of hydrolysis may be obtained in good yield. Thus, partially demineralized whey was hydrolyzed with pig trypsin in such an app. to prep. an hydrolyzate with NPN 65%. Under the same conditions, an NPN of only 60% was obtained when a single reaction vessel was used. [on SciFinder (R)]