Lyngby, Denmark VTT, P.O. Box 1000 (Tietotie 2), FI-02044 VTT (Espoo), Finland a r t i c l e i n f o a b s t r a c t Article history: Reliable test for checking cleanliness are needed to evaluate and validate the clean- Received 28 December 2005 ing process of fermentation tanks. The size of a fermentation tank can be several hundred