  QCD lattice simulations with 2+1 flavours typically start at rather large
up-down and strange quark masses and extrapolate first the strange quark mass
to its physical value and then the up-down quark mass. An alternative method of
tuning the quark masses is discussed here in which the singlet quark mass is
kept fixed, which ensures that the kaon always has mass less than the physical
kaon mass. It can also take into account the different renormalisations (for
singlet and non-singlet quark masses) occurring for non-chirally invariant
lattice fermions and so allows a smooth extrapolation to the physical quark
masses. This procedure enables a wide range of quark masses to be probed,
including the case with a heavy up-down quark mass and light strange quark
mass. Results show the correct order for the baryon octet and decuplet spectrum
and an extrapolation to the physical pion mass gives mass values to within a
few percent of their experimental values.
