Sourdough bread losses and sourdough cultures for sour beers

In Flanders, approximately 25% of all bread and bakery products are lost each year. Today, these bread losses go to cattle feed or biogas production, although in most cases this bread is still suitable for human consumption. By valorising these unavoidable bread losses in beer, breweries can contribute to the reduction of food losses. The aim of this study is to investigate whether the losses of sourdough bread that occur during bread production can be used for the production of sour beers. Specifically, sourdough bread was used as an adjunct in wort production. Sourdough cultures, collected in bakeries, were used for wort fermentation. Three different sourdough cultures, based on rye, spelt and wheat, were tested at three different fermentation temperatures (16°C, 22°C and 30°C) against a Safbrew's high yeast S-04 that served as a reference. All sourdough cultures were able to ferment the wort consisting of 20% sourdough bread, but not at each fermentation temperature. The rye and spelt sourdough cultures were not able to obtain an acceptable degree of fermentation at a temperature of 16°C, while this was possible at 22°C and 30°C. The sourdough beers obtained had a higher degree of attenuation, a higher alcohol content, a lower pH and a higher concentration of total titratable acids (TTA) than the reference beers. Sugar profiles showed that maltotriose concentrations in the sourdough beers were relatively high compared to the reference beers while maltose, maltotetraose, -pentaose, -hexaose, sucrose, and glucose were fully fermented. The yeast S-04 was able to ferment the smaller sugars up to maltotriose, larger sugar molecules remained untouched. All beers could be classified as 'sour beer' on the basis of TTA. After analysis, the biological triplicates of the respective sour beers were mixed and refermented in the bottle. Aromas of smoked meat, fruity and sour notes were observed in the different sourdough beers. The sourdough beers differed in flavour and appearance both from the reference and from each other.