β-lactoglobulin is an abundant whey protein in the milks of ruminant animals, yet is completely absent in humans. It has been intensively studied using countless biophysical techniques, however its physiological function remains elusive. Our work focuses on the comparison of the caprine and bovine orthologues of β-lactoglobulin. AUC has proved a useful complement to X-ray crystal structures and small angle X-ray scattering data to provide information on the oligomeric state of these proteins. In both solution and crystalline states they appear to be dimeric. We have also used membrane confined electrophoresis to characterise the effective charge on these molecules, identifying a lesser negative overall charge on caprine β-lactoglobulin which has the potential to affect interactions that occur within milk. A structural understanding of these proteins may provide useful insight into the relationships among the structural, nutritional, immunological and processing characteristics that distinguish cow and goat milk.