Brown seaweeds are a suitable substrate for biogas production through anaerobic digestion (AD). Since the carbohydrates' content is subjected to a seasonal variation, this research aimed to select the best harveking period of beach cast brown seaweed Laminaria sp. for methane production, while optimising the use of a beating pretreatment and the organic substrate concentration. Response surface methodology (RSM) was used to estimate the effect of the beating pretreatment in terms of pretreatment time (5-10-15 min) and organic matter concentration in terms of volatile solids (VS) (1-2.5-4%) on methane production. The highest methane yield of 342 +/- 17 ml g(-1) VS was observed during November at 1% of VS and after 5 min of pretreatment, while the lowest yields were registered in March with an average of 163 28 ml g-1 VS. However, an enhancement of 47% with respect to the untreated sample was achieved at 2.5% of VS and after 15 min of pretreatment, in March. (C) 2016 Elsevier Ltd. All rights reserved.