The impact of fermentation length and dough composition on the stability of liquid sourdough starters

Sourdough breadmaking on an industrial scale requires robust, well-performing starters that bring attractive characteristics to the product. The active nature of liquid starters provides a faster fermentation process compared to their dehydrated counterparts. However, liquid sourdough starters require meticulous management in order to maintain stability and functionality during cold storage at 4 °C. This study investigated the stability of three liquid sourdough starters during storage and also the impact of prolonged fermentation, the addition of diastatic malted wheat flour, and a neutralising agent (CaCO₃). The sourdough starters were evaluated for their microbial viability and metabolic activity at three individual time points during 16 weeks of cold storage. The microbial composition was analysed using culture-dependent and culture-independent methods, and metabolic changes were investigated using chromatographic methods. Two types of sourdough starter showed satisfying viability of lactic acid bacteria (> 7 log CFU/g) and metabolic stability throughout 16 weeks of cold storage. The introduction of malted wheat flour and CaCO₃ caused a decline in viability to <7 log CFU/g within 8 weeks in the third sourdough starter type and additionally revealed an ongoing metabolic activity of this sourdough starter during cold storage. Prolonged fermentation influenced the free amino acid profile, whereas adjusting the sourdough starter formula resulted in a different fungal microbiota and increased levels of fermentable substrates (maltose), organic acids (lactic acid), and aromatic compounds (alcohol and aldehydes). These findings provide stakeholders and researchers in sourdough fermentation technology with new insights concerning the stability of cold-stored liquid sourdough starters.