Hydrochars were prepared by hydrothermal carbonization (HTC) of maize silage previously treated at 55 degrees C in a two-stage solid-state reactor system. The HTC was carried out in a 1-L stirred pressure reactor with h pH regulation by citric acid. The treated silage carbonized at relatively mild conditions (190 degrees C, 2 h), and the hydrochars showed mainly amorphous macro-size features with a carbon content of 59-79% (ash-free, dry) and a higher heating value of 25-36 MJ kg(-1). Temperature was the main influencing factor. The surface area according to Brunauer-Emmett-Teller (BET) analysis was highest at 190 degrees C (12.3 m(2) g(-1)). Based on these results, the hydrochars are potentially interesting for applications such as an alternative fuel or a soil conditioner. (C) 2011 Elsevier Ltd. All rights reserved.