From Bakery Leftovers to Brewing Sustainability: Fermentation of Spent Grain with Yarrowia lipolytica and Lactobacillus acidophilus

The use of bakery leftovers as a substitute for malt in brewing represents a sustainable approach that reduces costs and waste. In this paper, the fermentation of brewer’s spent grain, a byproduct of beer production, is integrated with the use of non-conventional yeasts to unlock the potential of yeasts beyond the common Saccharomyces species. This creates a circular system where byproducts are efficiently utilized, fostering sustainability and innovation in food production. This study assesses the fermentative capabilities of the non-conventional yeast Yarrowia lipolytica and the lactic acid bacterium Lactobacillus acidophilus DSM 20079 on brewer’s spent grain, a byproduct from brewing beer with old wheat bread and barley malt. Both hydrolyzed with a cell-wall-degrading enzyme complex and non-hydrolyzed brewer’s spent grain were evaluated for key fermentation indicators such as the number of microbial cells, total titratable acidity, pH, reduced sugar content, and fatty acid composition. The findings reveal that Yarrowia lipolytica effectively fermented brewer’s spent grain without prior hydrolysis, maintaining a balanced fatty acid profile. The combined action of both microorganisms provided optimal fermentation outcomes, offering a promising approach for valorizing brewer’s spent grain, reducing waste, and promoting a circular economy in the brewing and food industries.