Microbial Ecology of Traditional Beer Fermentations

Microbial acidification, alcoholization, and aroma production during spontaneous lambic beer production

“…Based on the primary fermentation process applied, a general classification of beer fermentation types can be made for the production of four different categories of beer: (i) bottom fermentation of water, barley malt, and hop with Saccharomyces bayanus or Saccharomyces pastorianus (synonym Saccharomyces carlsbergensis ) for the production of lager beers (light‐colored pils beers) in fermentation vessels; (ii) top fermentation of water and a variety of ingredients (barley malt, hops, other cereals, herbs, and/or spices, most of them contributing to aroma and mouthfeel) with Saccharomyces cerevisiae for the production of ales (e.g., blond, amber and dark ales, stout beers, and trappist beers) in fermentation vessels, commonly followed by bottle refermentation (secondary fermentation); (iii) non‐spontaneous, mixed fermentation, traditionally carried out with an in‐house starter culture that consists of yeasts and lactic acid bacteria (LAB) in fermentation vessels, followed by maturation in vertical oak barrels, for the production of red and red‐brown acidic ales, or followed by maturation in metal tanks for the production of old‐brown acidic ales; and (iv) spontaneous, mixed fermentation, traditionally obtained through air inoculation of the wort in an open coolship, followed by fermentation and maturation in horizontal wooden barrels (oak or chestnut), for the production of acidic ales of the lambic type. Here, fermentation is carried out by enterobacteria, yeasts, LAB, and acetic acid bacteria (AAB) . These four fermentation strategies have been used in Belgium for hundreds of years.…”

“…Belgium is particularly known for its traditional spontaneous mixed fermentation beers, such as lambic beers, which harbor more complex microbiota than the non‐spontaneously mixed fermented beers (Flemish red‐brown and old‐brown ales) . These acidic lambic beers are among the oldest commercial and hence ancient brewing styles that are still used and they are gaining interest worldwide due to their unique flavor profile, which cannot be mimicked by pure culture fermentations …”

“…). The mixed fermentation and maturation process can proceed for up to three years and is characterized by a microbial succession of different yeast and bacterial species . Different kinds of spontaneous mixed fermentation beers exist now, with a majority still being produced in Belgium by traditional, specialized breweries, located near the Senne river valley and in the Payottenland around Brussels.…”

“…The use of unmalted wheat and the mashing method applied (often turbid mashing) contribute to a highly dextrinous wort. During turbid mashing (also called slime cooking), part of the mash is separately cooked during two successive mashing steps, resulting in wort that is only partially subjected to all the enzymatic rest temperatures . After mashing, the wort is boiled with the addition of, typically, old, whole hop bells, which contain a less bitter taste than fresh hops, thereby avoiding interference with the tart character of the beer .…”

“…They enhance the microbiological stability of the beer, even outperforming iso‐ α ‐acids for that matter . The use of old hop bells necessitates a long boil of 3–5 h as a consequence of their high content of oxidized resins, which can give rise to off‐flavors . After wort boiling, the wort is transferred to an open metal vessel (coolship), where it cools overnight, open to the air, allowing inoculation of environmental microorganisms.…”