  We measure the diffusion constant for Chern-Simons number for classical,
lattice SU(3) Yang-Mills theory, using a generalization of the topological
definition of Chern-Simons number developed recently by Moore and Turok. The
diffusion constant is much larger than that for SU(2), even before the ratio of
coupling constants has been accounted for, which implies that chiral quark
number is efficiently destroyed by strong processes during the electroweak
phase transition. For the physical value of \alpha_s we estimate the decay time
for chiral quark number to be about 80/T, although various systematics make
this number uncertain by about a factor of 2.
