The present invention provides methods of processing biomass containing a cellulosic material that include contacting the cellulosic material with magnesium hydroxide to adjust the pH of the material before and/or after a high temperature and high pressure pretreatment step. The use of magnesium hydroxide provides a safer alternative to using ammonium hydroxide for pH adjustment, a more stable, buffered environment for improved operability in pH control, with similar or improved conversion of biomass to fermentable sugars, and similar or improved reduction of inhibitors during the subsequent hydrolysis or saccharification process.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 This invention was made with government support under Grant Number "Federal Opportunity DE-FOA-0000096" awarded by the Department of Energy. The government has certain rights in the invention.