TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Apparatus: The reactor is a batch steam explosion reactor or a continuous reactorPreferred Feedstock: the lignocellulosic feedstock comprises softwood, hardwood, agricultural residues, municipal solid waste (construction lumber), corn refining intermediates and residues. the softwood is Douglas Fir, White Fir, Ponderosa Pine, Sitka spruce and/or Hemlock.Preferred Compounds: The dilute acid comprises H2SO4, HCl, HNO3, SO2 or any strong acid which effects pH values below 3 and the metal salt catalyst comprises ferrous sulfate, ferric sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum, chloride and magnesium sulfate.Preferred Method: The acid is H2SO4 or SO2 and the residence time is 1-60 minutes for first stage hydrolysis and 1-10 minutes for the second stage hydrolysis. The temperature for hydrolysis is 130-220degreesC for first stage hydrolysis and 190-240degreesC for the second stage. The temperature for hydrolyzing to the monomeric sugars in the first flash tank is 120-140degreesC and the residence time is 1-3 hours. The dewatering is carried out by drying and the acid concentration in the liquid in the biomass before subjecting to first or second stage hydrolysis is 0.3-4 wt.% and the concentration of the metal salt is between 0.2-25 mmole/L. When the acid is SO2 dewatering (if necessary) of the feedstock is carried out to 40-60% wet wt.% prior to SO2 impregnation, and the acid concentration in the liquid in the biomass before subjecting to first or second stage hydrolysis is between 0.3-6 wt.%. In step (g) air sparging (in the first fermentor of the first stage fermentation train) sufficient to promote yeast growth is about 0.05 vvm. In step (f) the lower temperature in the second flash tank is 95degreesC. In step (h) the whole slurry from the second stage hydrolysis reactor is fermented in the second train of fermentors using yeasts from the first stage fermentors. If gaseous SO2 is used then the dewatering step (b) is omitted. the drying is done using heated air, nitrogen, carbon dioxide and/or superheated steam. The extract is recovered hydrolyzate liquor and the pretreated solids are insoluble solids. EXAMPLE - None given.