Brewers' spent grain (BSG) is a low-cost by-product of the brewing process. BSG liquor names the liquid components of BSG, mainly glucose, maltose, and long-chain -1,4-glycosidic bond glucose oligomers. These substances should be separated in existing BSG biorefineries, as they might lead to an increased formation of microbeinhibiting compounds in well-established hydrothermal/enzymatic saccharification processes. In most cases, this liquid fraction is discarded. The present study presents for the first time an optimized process with BSG liquor for the purpose of producing bulk chemicals (e.g., lactate) in relevant concentrations. The process comprises the application of yeast extract, produced from own brewing processes, as the sole supplemented complex constituent in a simultaneous fermentation and saccharification process. Kinetic parameters for the final optimized process conditions with the organism Lactobacillus delbrueckii subsp. lactis were: maximum specific growth rate µ max = 0.47 h −1 , maximum lactate concentration c Lac, max = 79.06 g L −1 , process yield Y PS = 0.89 g Lac g Sugar −1 , lactate production rate q P = 4.18 g Lac g CDW −1 h −1 , and productivity P 15 h = 4.93 g Lac L −1 h −1 . BSG liquor, linked with yeast extract from Brewers' yeast, can be a promising substrate for further bioprocess engineering tasks and contribute to a holistic and sustainable usage of Brewers' spent grain. K E Y W O R D S biorefinery, brewers' spent grain (BSG) liquor, fermentation, lactate, Lactobacillus delbrueckii subsp. lactis 1 INTRODUCTION Brewers' spent grain (BSG) is the most abundant by-product of the brewing process and available in large quantities since the worldwide annual beer production was 1.95 million hL in 2017 [1]. As 0.2 kg of BSG accumulate from the production of 1 L beer [2], this resulted in about 39 million metric tons Abbreviations: BSG, brewers' spent grain; CDW, cell dry weight; MRS medium, cultivation medium by De Man, Rogosa, Sharpe.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Ein Bioraffineriekonzept für (Bier‐)Treber wird vorgeschlagen, bei dem im Gegensatz zu bestehenden Konzepten wasserlösliche Komponenten durch Pressen abgetrennt und als Grundlage für eine Milchsäurefermentation mit Lactobacillus delbrueckii subsp. lactis verwendet werden. Die verbleibenden strukturellen Kohlenhydrate des Treberrückstandes werden durch hydrothermale und enzymatische Vorbehandlung in fermentierbare Zucker überführt. Es entstehen deutlich weniger Nebenprodukte, die das Wachstum von Mikroorganismen inhibieren können, als bei der Nutzung von nicht abgepresstem Treber.

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