Fermentation is a very important bioprocess for the production of drugs, food products, beverage and for animal cell line culture etc. The substrates used in these processes are expensive. So on-line monitoring of contamination in a fermentation process is very essential in industries. A new method for contamination detection is being proposed in this paper. This is a software-based method. In this new method, the state variables of the process are used to detect contamination of the process.