BACKGROUNDInstant coffee production generates large amounts of a waste known as spent coffee ground (SCG), which is rich in carbohydrate (approximate to 50%), oil and aromatic compounds. RESULTSSteam pretreatment by itself solubilised up to 10.7% of the SCG mass, which was recovered as soluble solids in the liquor from pretreatment. The highest extent of soluble solid recovery from pretreatment itself (10.7%) was obtained at 210 degrees C/15 min, while milder conditions (150-190 degrees C/10-12 min) recovered 2.6% soluble solids. Mannanase (recombinant strain of Yarrowia lipolytica) and cellulase (Acremonium, Bioshigen Co.Ltd, Japan) had an additive effect, with no indication of synergism observed. The best combinations of mannanase/cellulase cocktail for enzymatic hydrolysis were 0.5/0.82% and 0.01/0.91% (w/w), releasing 20.6% (g per 100 g raw SCG) and 22.6% (g per 100 g pretreated SCG) of soluble solids from untreated and pretreated SCG, respectively. By combining soluble solids recovered from steam pretreatment with the soluble products from subsequent enzymatic hydrolysis, a yield of 27.65% (g per 100 g SCG) was achieved. CONCLUSIONThe pretreatment was effective in generating a material more amenable to enzyme action, thus requiring reduced enzyme dosages for subsequent hydrolysis compared with untreated SCG. The combined process showed significant technical feasibility for re-use SCG and may be considered to produce additional instant coffee product. (c) 2014 Society of Chemical Industry