The stability of Clostridium butyricum TISTR 1032 during biohydrogen fermentation of non sterile food waste in 5-L semi-batch operation was investigated under controlled and uncontrolled pH conditions at the initial pH 6, and 37 degrees C. Profiles of carbon mass balance, microbial community and metabolite dynamics were used to evaluate the process efficiency. The results showed that under the uncontrolled pH condition, the maximum hydrogen yield, production rate and specific production rate were 362 mL H-2 g(-1) VS, 695 mL h(-l) and 174 mL H-1 L-1, respectively while under the controlled pH condition, those were 350 mL H-2 g-1 VS, 1092 mL H-1 and 273 mL h(-1) L-1, respectively. Regarding the carbon distribution, food waste was still remained in the solid fraction more than 30% at which the maximum hydrogen production was achieved for all cases. The main factor, which controlled the route of fermentative process under uncontrolled pH condition was acidic condition while acetogenesis was the major effect for the production stability in the controlled pH condition. DGGE profiles showed that C. butyricum TISTR 1032 was still the dominant group in the reactor in both conditions. However, Klebsiella oxytoca, Strap-hylococcus spp., Enterobacter spp., Lactococcus spp. and Acinetobacter sp. were observed for all cases. The metabolite analysis revealed the correlation of K. oxytoca and solventoganesis process under the uncontrolled pH condition while the presence of Lactococcus spp. was related to lower yield of the hydrogen production under the controlled pH condition. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.