The FDA requires biopharmaceutical manufacturers to understand and control sources of variation according to the risks they present to process and product. Cell culture media and feeds have been shown to affect cellular performance, product quality, or both. The evolution of media formulas to those that are serum free and chemically defined poses both a challenge and an opportunity. The challenge is identifying which of the many components have the greatest impact on cells and the molecules they produce. The opportunity comes from the ability to uncover potential sources of variation previously masked by serum or other undefined additives, such as hydrolysates and lipid complexes. Advances in analytical methods, paired with effective, risk-based assessment methods, enhance understanding and help mitigate risks, enabling management of variation to the highest extent possible.