Dilute acid pretreatment is performed by soaking the material in dilute
acid solution and then heating to temperatures between 140 and 200 ◦C for
a certain time (from several minutes up to an hour). Sulphuric acid, at concentrations
usually below 4 wt%, has been of most interest in such studies as
it is inexpensive and effective. The hemicellulose is hydrolysed and the main
part is usually obtained as monomer sugars. It has been shown that materials
that have been subjected to acid hydrolysis may be harder to ferment because
of the presence of toxic substances [26–28].