Yeast biodiversity of traditional and modern hop beer fermentations

Old brewing cellars and natural resources related to brewing history were investigated for their culturable yeast microbiota. A total of 164 wild yeast strains were isolated in 2015-2018, belonging to five Saccharomyces species and 41 non-Saccharomyces yeast species. The five Saccharomyces species found were S. cerevisiae (seven strains), S. paradoxus (22 strains), S. jurei (one strain); S. uvarum x eubayanus (five hybrid strains) and S. uvarum (2 strains) and were isolated out of/from containers from brewery cellars, an outside vat/tub, oak (Quercus robur), ash (Fraxinus excelsior), hornbeam (Carpinus betulus), hazel bush (Corylus avellana), apple (Malus domestica), medlar (Mespilus germanica), elm (Ulmus sp.), wild service berry (Sorbus torminalis), white willow (Salix alba), hops (Humulus lupulus) and spent grains. A pure European line of the yeast species S. eubayanus could not be found. However, it was possible for the first time to isolate a S. eubayanus × S. uvarum hybrid from a beer bottle that was about 70 years old. For the first time, a S. jurei isolate from ash tree was found. Ten selected Saccharomyces strains underwent a fermentation-related rapid characterization.