  The high precision to which the standard model has been confirmed implies
that new physics effects have to be small in the observed processes. Together
with the outstanding precision expected from present and future collider
experiments this renders the evaluation of subleading SM contributions
necessary. For the "golden mode", B_d to J/Psi K, these so-called "penguin
pollution" terms can be controlled by using flavour symmetry relations. A
recent analysis is presented which yields a stronger bound on the maximal
penguin influence than previous ones and shows how the corresponding
uncertainty can be reduced with coming data.
