Free water in excess of 65 % MC can be extracted by compressing the biomass with a press. In this way the MC can be reduced to about 20 %. To remove the remaining water, the biomass must either be air or oven dried. The drying time depends on the particle size and the composition of the biomass used. Typically wood chips reach a MC of 10-12 % after a few weeks of air drying in the Western Cape in South Africa and this process is faster for smaller particles (Sturos et al. 1983; Wondifraw 2010). Drying in a kiln or oven can remove the water entirely, depending on the time and temperature employed. Torrefaction (see Chap. 7) is an alternative to drying, resulting in products highly suited for thermochemical processing that can be stored for long periods of time.

Any moisture present in biomass reduces its calorific value. For combustion, gasification and pyrolysis the MC should therefore be as low as possible. Acceptable values for most reactor types are between 10 and 20 % (Schuck 2006; McKendry

2002) . If too much moisture is present, much of the energy contained in the biomass is used to evaporate the water. Furthermore, biomass with a high MC cannot generate certain compounds when pyrolysed, which also affects the acidity and composition of liquid produced (Guillen and Ibargoitia 1999).

On the other hand, moisture is desirable for biochemical conversion, such as fermentation and anaerobic digestion (see Chap. 7) and the biomass is kept as wet as possible, typically with MC values between 80 and 90 %.