The Universe contains much more matter than antimatter, which is probably the result of processes in the early Universe in which baryon number was not conserved. These processes may have occurred during the electroweak phase transition, when elementary particles first acquired mass(1-4). It is impossible to study directly processes relevant to the early Universe, because of the extreme energies involved. One is therefore forced to investigate laboratory systems with analogous phase transitions. Much of the behaviour of superfluid He-3 is analogous to that predicted within the standard model of the electroweak interaction(5). Superfluids and liquid crystals have already been used to investigate cosmic-string production(6-11); here we describe experiments on He-3 that demonstrate the creation of excitation momentum (which we call momentogenesis) by quantized vortices in the superfluid. The underlying physics of this process is similar to that associated with the creation of baryons within cosmic strings, and our results provide quantitative support for this type of baryogenesis.