  We study the transition from npe-type nuclear matter (consisting of neutrons,
protons, and electrons) to matter containing strangeness, using a Walecka-type
model predicting a first-order kaon-condensate phase transition. We examine the
free energy of droplets of K-matter as the density, temperature, and neutrino
fraction are varied. Langer nucleation rate theory is then used to approximate
the rate at which critical droplets of the new phase are produced by thermal
fluctuations, thus giving an estimate of the time required for the new (mixed)
phase to appear at various densities and various times in the cooling history
of the proto-neutron star. We also discuss the famous difficulty of
"simultaneous weak interactions" which we connect to the literature on
non-topological solitons. Finally, we discuss the implications of our results
to several phenomenological issues involving neutron star phase transitions.
