Ecology of red-brown acidic beers
West of the Scheldt in Belgium, non-spontaneous mixed acid beer fermentation was originally applied for beer production where hops were replaced by herbs (called ‘gruyt'). Non-spontaneous mixed fermentation is used in two types ofBelgian acidic ales, namely the red acidic ales of south-west Flanders (Roeselare) and the red-brown acidic ales that are produced in south-west and south-east Flanders. The red acidic ales of south-west Flanders were traditionally produced using an in-house starter culture that contains yeasts and LAB, by the reuse of the starter in every fermentation batch (Martens et al., 1997). The level of bacteria is kept low by acid washing (mainly with phosphoric acid) of the yeast suspension (Martens et al., 1997). These ales have a vinous acidic character and their production starts with mashing of malted barley and cooked unmalted maize (Martens et al., 1997). The main ethanol fermentation phase proceeds for about seven days and is followed by a secondary lactic acid fermentation phase that proceeds for another 4-5 weeks (Martens et al., 1997). Finally, a long maturation phase of 20 to 24 months occurs in large oak casks and P. damnosus and Pediococcus parvulus, together with Brettanomyces spp. and AAB (supported by natural micro oxygenation through the wood) are an active part of the microbiota during this phase (Martens et al., 1997). These results were confirmed by a recent study using BAS on red-brown finished beer samples, which revealed that the most abundant microbial species present in these beers were P. damnosus, B. bruxellensis and A. pasteurianus (Snauwaert et al., 2016). The draft genome representative strain of P. damnosus, isolated from a maturation phase sample of these beers, was recently sequenced (Snauwaert et al., 2015). Furthermore, additional operational taxonomic units were assigned to Candida, Lactobacillus and an unclassified fungal community member. This ‘tandem' fermentation process (the main fermentation phase followed by cask maturation) was imported into Belgium around 1860 from northern England, where it was used for the production of old English Porter beer (Claussen, 1904; Martens et al., 1997). Brettanomyces spp. were present in old English Porter beer until the production process was altered and stainless steel fermentation vessels were used instead of wooden casks, indicating that contact with wooden casks is an important feature for supporting the growth of this yeast (Martens et al., 1997). The production of red-brown acidic ales is very similar, with the fermentation being initiated by re-pitching of LAB-harbouring yeast starter cultures and the use of open fermentation vessels from which the yeast is harvested at the end of the fermentation phase, followed by maturation in oak vessels (Martens, 1996; Martens et al., 1997). Red- brown acidic ales differ from old brown ales in that the latter beers are not oak-aged, but they are also produced in south-east Flanders.