One method of pretreatment is to soak the wood with diluted acids (with concentrations around 4%). This converts the hydroloze hemicellulose into monosaccharaides. When pretreatment is done with bases (for instance sodium or potassium hydroxide) this destroys the structure of the inherent lignin. This changes the structure from crystalline to amorphous. Another pretreatment method is to pretreat hydrothermally. This offers advantages such as no toxic or corrosive solvents are needed, nor are special reactors, and no extra costs to dispose of hazardous chemicals.