•Particle size <120 µ enables above 95% hemicellulose recovery.•Lower substrate concentration gives higher xylooligosaccharides yield.•Produced XOS comparable to commercial XOS in terms of gas and acid levels.•Short chain oligosaccharides produce higher level of acetate. Almond shell, a by-product obtained from the nut industry, was valorised into low degree of polymerisation xylooligosaccharides using alkaline pretreatment and enzymatic hydrolysis. The effect of particle size on hemicellulose recovery upon pretreatment was studied using 1 and 2 M NaOH. It was observed that particle size significantly influences hemicellulose recovery, as particles below 120 µm resulted in near complete recovery at 2 M NaOH. Enzymatic hydrolysis of hemicellulose was optimised using response surface methodology, to obtain efficient xylooligosaccharides production at low enzyme dose and high substrate concentration. For higher XOS yield, an enzyme dose of 10 U and substrate concentration <2% was optimal. The in-vitro human faecal fermentation study revealed no significant difference in gas and short chain fatty acid level among substrates evaluated. It was observed that short chain oligosaccharides produce higher level of acetate than medium chain oligosaccharides.