Optimization procedures such as experimental designs (DOE) improve pretreatment efficiency, and chemical characterization of the starting material becomes necessary to assess the efficiency. Hydrothermal pretreatment (HTP), also called auto-hydrolysis (AH), is one of the most economically interesting pretreatments since only water work as reactant. AH pretreatment optimization can reach a liquor rich in monosaccharide units at the same time that a low content of toxic compounds to biological processes (i.e., 2-furfuraldeído (FUR) e 5-hidroximetil-2-furfuraldeído (HMF). Early, AH pretreatment variables temperature (T), time (t), solid-liquid ratio (SLR) and stirring (RPM) were studied by a 24 factorial design. A new HPLC analytical method for quantifying acids that can be formed during AH (i.e., formic, acetic, glucuronic and levulinic acids) has been developed using Bio-Rad Aminex HPX-37H column in a Shimadzu Prominence HPLC. In general, the most significant factors were T and t; higher levels of T improved hemicellulose depolymerization whereas lower levels of t disfavoured pentoses degradation to FUR. At 220 ºC, 60 min, 20 % of SCB and 60 rpm it was possible to achieve a yield of 109.84 g kg-1 of pentoses (i.e., xylose and arabinose) with only 14.42 g kg-1 of FUR. Under these same conditions, the acid content in the liquor was 15.1 g kg-1, 12.2 g kg-1, 39.8 g kg-1 and 55.5 g kg-1 for glucuronic, formic, acetic and levulinic acids, respectively.