This study established a novel process using sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) for robust and efficient bioconversion of softwoods. The process consists of sulfite treatment of wood chips followed by mechanical size reduction using disk refining. The softwood substrate obtained showed excellent digestability, i.e., over 90% cellulose conversion of substrate with enzyme loading of about 14.6 FPU cellulase plus 22.5 CBU â-glucosidase per gram of od substrate after 48 hours hydrolysis. The glucose yield from enzymatic hydrolysis of the spruce substrate per 100 g of untreated od spruce wood (glucan content 43%) was about 37 g (excluding the dissolved glucose during pretreatment). The pretreatment altered the wood chips which reduced electric energy consumption for size reduction to only about 19 Wh/kg od untreated wood, or about 19 g glucose/Wh electricity. Furthermore, SPORL produced substantially low amounts of fermentation inhibitors, hydroxymethyl furfural (HMF) and furfural, of about 5 and 1 mg/g of untreated od wood, respectively. In addition, similar to better results were achieved when SPORL was applied to Red Pine. By building on the mature sulfite pulping and disk refining technologies already practiced in the pulp and paper industry, SPORL has very few technological barriers and risks for commercialization.