Efficient valorisation of lignocellulosic biomass is a great opportunity for sustainable waste management and the production of high-value compounds due to its high availability and organic matter content. This study investigates medium-chain carboxylate (MCC) production from a cellulose-xylan mixture, focusing on the influence of reactor configuration: a one-stage sequential batch reactor (SBR), a two-stage SBR, and a sequential fed-batch reactor (SFBR). The operational conditions, including hydraulic retention time (HRT), volume exchange ratio (VER) and pH, were systematically varied to enhance lactate production and its subsequent elongation into MCCs. Results demonstrated that shorter HRTs and pulsed feeding strategies improved substrate hydrolysis and lactate availability, steering the fermentation pathway towards MCC production. SFBR resulted in the optimal reactor configuration since the two reaction phases generated by the two pulse-feedings enhanced, firstly, lactate production (high load, short time), and secondly, caproate production (low load, long time). This mechanistic strategy, using model substrates, offers valuable insights for scaling up MCC production from real lignocellulosic feedstocks, contributing to the development of sustainable biorefineries.