A novel fermentation system for the production of Spanish-style green table olives

Abstract

The traditional technology of fermenting Spanish-style green table olives in underground fibre-glass containers has remained largely unchanged since the late 1960s. This study introduces a novel fermentation system based on interconnected stainless-steel containers operated under vacuum conditions and equipped with two pumps: one for brine recirculation and another for gas purging. The primary goals of this new system are to enhance homogeneity among fermentation vessels, facilitate gas release, and improve cleaning and disinfection procedures. The conventional system favoured the growth of lactic acid bacteria, resulting in higher titratable acidity (1.10 % vs. 0.67 % in stainless-steel containers), although both systems achieved similar final pH levels (∼4.2). Traditional fermentation also produced olives with superior colour and overall acceptability. In contrast, the new system showed lower variability across most physicochemical and microbiological parameters, indicating improved process uniformity. It also favoured yeast growth, enhanced CO2 release from the fermentation medium, improved fruit texture, supported more consistent inoculum imposition, and was associated with lower combined acidity at the end of the process (0.118 Eq/L vs. 0.173 Eq/L in the traditional system). Metataxonomic analysis revealed greater microbial diversity (both bacterial and fungal) in the conventional system. In contrast, the stainless-steel system showed a higher prevalence of Lactiplantibacillus sequences (89.01 % vs. 64.9 % in fibre-glass containers). Foodborne bacterial pathogens were not detected. Moreover, post-fermentation cleaning and disinfection were more effective in stainless-steel containers (99.29 % of mesophilic aerobes were removed) than in fibre-glass ones (96.23 %). Overall, our findings support the modernization of table olive fermentation, demonstrating that the proposed system can reduce spoilage risks and improve product standardization.