Symmetry breaking phase transitions occurring in the early Universe are expected to leave behind long-lived topologically stable structures such as monopoles, strings or domain walls1–6. Here I discuss the analogy between cosmological strings and vortex lines in the superfluid, and suggest a cryogenic experiment which tests key elements of the cosmological scenario for string formation. In a superfluid obtained through a rapid pressure quench, the phase of the Bose condensate wavefunction—the 4He analogue of the broken symmetry of the field-theoretic vacuum—will be chosen randomly in domains of some characteristic size d. When the quench is performed in an annulus of circumference C the typical value of the phase mismatch around the loop will be ∼(C/d)1/2. The resulting phase gradient can foe sufficiently large to cause the superfluid to flow with a measurable (mm s−1), randomly directed velocity.