Chain elongation (CE) processes convert organic waste into medium-chain fatty acids such as caproic acid, offering a waste management strategy while producing value-added chemicals that support circular economy development. However, product inhibition caused by undissociated caproic acid remains a critical challenge limiting the efficiency of traditional CE processes, occurring in both lactate-driven (pH 5.0–6.5) and ethanol-driven (pH 5.0–7.0) chain elongation. This study developed an innovative lactate-driven fermentation strategy operating at neutral pH (initially pH 7.0), where pH naturally increased to pH 7.5–8.0 without external adjustment, effectively shifting acid-base equilibrium to dramatically reduce undissociated caproic acid inhibition. Under these conditions, microbial enrichment resulted in a functional community dominated by Anaerococcus (relative abundance of 48.2 %), achieving a caproate concentration of 31.6 g COD/L with 68.3 % product specificity in synthetic lactate medium. Metagenomic analysis revealed that Anaerococcus possessed the genetic potential for caproate synthesis through lactate oxidation and reverse β-oxidation pathways, with Pseudoramibacter (17.4 % relative abundance) also potentially contributing to caproate synthesis. The process demonstrated remarkable stability when applied to actual food waste conversion, maintaining consistent microbial community structure. This distinctive neutral pH fermentation system effectively addresses product inhibition challenges, offering significant potential for efficient valorization of lactate-rich waste streams in circular bioeconomy applications.