A direct numerical simulation of a turbulent flow field with a lattice BGK method is presented. A spatial coarse graining of the numerical results is compared with the expected LBGK dynamics for a flow field on a reduced lattice size. This comparison permits to exhibit subgrid properties of the fluid which are not resolved on the coarse lattice. As expected from existing subgrid models, an effective viscosity can be measured that increases when the lattice is coarse grained. Turbulence models based on an effective viscosity are particularly interesting in a lattice Boltzmann simulation, due to the linearity of the propagation operator.