This study evaluated the impact of k-casein (k-CN) protein phenotype (AA (n = 18), AB (n = 18), AE (n = 5), BB (n = 3)) in the raw milk of 44 individual Holstein cows from a single farm on coagulation properties using diffusion wave spectroscopy. k-CN variants were analyzed using a newly developed LC-MS method in individual milk samples, and relative milk protein fractions were quantified by LabChipanalysis. k-CN fractions expressed in the percentage of total milk protein, total casein, and b- and k-CN were then calculated. The gross composition of the individual milk samples and variation between individual cows was analyzed and was rather large, as expected. Traits were analyzed using an ANCOVA model with pH as a covariate. Our results showed that mean percentages of k-CN fractions increased for k-CN phenotypes in the order AA < AE < AB < BB. Rennet coagulation time was slightly affected, but curd firmness was significantly affected by k-CN phenotype (BB > AE > AB > AA) when controlling for pH.