Non-conventional yeasts for producing alternative beers

Since immemorial time beer is the product of wort fermentation catalyzed by the cells of two main yeast species, namely, Saccharomyces cerevisiae and Saccharomyces pastorianus, with hop addition. However, in recent years the beer market changed completely and novel types of beers, such as low-alcohol and low-calorie beers and spontaneously fermented or flavored beers, have become very popular. These different beers vary for the nature and amounts of water, cereals, hops, and other additives, techniques used for production, storage, and consumption, and also yeasts used as starter. Indeed, some non-conventional yeasts have been recently proposed as starter cultures for brewing. This chapter provides a comprehensive review of the most recent papers describing yeast species diversity used in brewing industry or found in spontaneous fermented beers. Many species were described for their fermentative aptitude as a single or co-starter, either at lab or pilot scale and, rarely, at the industrial scale. Ascomycetous species are generally used but a member of Basidiomycota (Mrakia sp.) was also considered. A particular focus in the chapter is dedicated to flavor production and to spontaneous fermentation.