Protein hydrolysates have long been touted as effective cell culture additives for improving both cell density and product titer. However, typical media optimization studies rarely consider multiple different products or their interaction (either with each other or with the basal media). This study documents the successful replacement of animal serum in Chinese hamster ovary (CHO) cell culture using a combination of hydrolysate products while elucidating often-overlooked interaction effects. Two design-of-experiments (DOE) mixture designs were used to determine the effect of eight plant and yeast-based hydrolysates and their interactions on cell density. Among the hydrolysates, plants were generally found to have positive effects when utilized in combination, while yeast hydrolysates experienced more negative effects in combination with each other. The addition of either a combination of cotton and wheat or individual Hy-Yest™ 466 to aDMEM was found to achieve similar growth to 5% serum, outperforming other hydrolysates. In contrast, adding the same hydrolysates to chemically defined commercial media resulted in growth inhibition. The combination of observed interactions between the various hydrolysate products and the basal media (as well as general batch-to-batch variability) reinforce the need for robust experimental design in further development of hydrolysate additives for cell culture media optimization.