  We study aspects of the pion condensation in two-flavor neutral quark matter
using the Nambu--Jona-Lasinio model of QCD at finite density. We investigate
the role of electric charge neutrality, and explicit symmetry breaking via
quark mass, both of which control the onset of the charged pion $(\pi^c)$
condensation. We show that the equality between the electric chemical potential
and the in-medium pion mass, $\mu_{e}=M_{\pi^-}$, as a threshold, persists even
for a composite pion system in the medium, provided the transition to the pion
condensed phase is of the second order. Moreover, we find that the pion
condensate in neutral quark matter is extremely fragile to the symmetry
breaking effect via a current quark mass $m$, and is ruled out for $m$ larger
than the order of 10 keV.
