Water balances, based on the evaluation of water released from the fer
mentor, were estimated in a solid-state fermentation process performed
without forced aeration. It was proved that the net gain or loss of w
ater during the course of the process depends on the dry weight of the
solid substrate at the beginning of the process and also on the initi
al water activity. A linear relationship was found between the wet wei
ght losses of cultures recorded after the end of the growth period and
the initial dry weight of the substrate which enables the evaluation
of the water released from om the vessels. These values were included
into water balances from which it was possible to calculate the water
produced by metabolism of carbohydrates, which was estimated at 0.40 m
ol of H2O per C-mol of glucose consumed.