Biology is playing an increasingly important role in the chemical engineering curriculum. We describe a set of experiments we have implemented in our Undergraduate Laboratory course giving students practical insights into membrane separation processes for protein processing. The goal of the lab is to optimize the purification and concentration of a protein by hollow-fiber, tangential-flow ultrafiltration. Experiments guide the students to an appreciation for concentration polarization, i.e. the buildup of a concentrated layer of solute on the membrane surface resulting from opposing processes of convection to the membrane surface and removal from the surface by diffusion and tangential flow. The experiment draws upon concepts the students will have seen in fluid mechanics, mass transfer, and separations courses. Optimization, the process of compromising between opposing phenomena, is demonstrated by having the students design a purification and concentration process that minimizes processing time.