The aim of this experiment was to improve the washing process during in vitro estimation of degradation rate of starch particles. The knowledge of degradation rate of starch particles in the rumen is needed to enhance micro-bacterial protein synthesis and energy supply for dairy cows. The washout of very small particles of starch (M-fraction) in the rumen prevents determination of its degradation rate in situ. However, it is possible to measure in vitro degradation rate of both a non-washable, potentially degradable fraction (D) and the M fraction.