Growth Study, Metabolite Development, and Organoleptic Profile of a Malt-Based Substrate Fermented by Lactic Acid Bacteria

The objective of this study was to investigate the fermentation of barley malt extract by four different lactic acid bacteria (LAB) species and to analyze the effect on biological, physicochemical, and organoleptic attributes of the resulting beverages. Malt and wort were analyzed following the Methodensammlung der Mitteleuropaischen Analysenkommission (MEBAK). Sugars and organic acids were evaluated using HPLC, while aroma compounds and ageing indicators were quantified using a head-space GC-FID. Unhopped wort was able to support the growth of all LAB during the whole experiment time (120 hr), with a cell count increase up to 3.63 log orders. The strain-specific preferences for carbon and nitrogen sources led to significant differences in the accumulation of metabolic byproducts (i.e., organic acids and flavor-active compounds released in the medium). LAB fermentation lowered the amount of some Strecker-aldehydes (2- and 3-methylbutanal and 2-phenylacetaldehyde) carrying "malty" off-flavors and increased dairy-related aroma compounds such as diacetyl and acetoin ("buttery"). The fermented samples were sensorially distinct and described with "bready", "yeasty", "yogurty", or "honey" attributes. In general, LAB fermentation conferred flavor complexity to wort. Forced ageing of the fermented samples led to a large increase of "staling" indicators but these samples improved organoleptic stability compared with the unfermented control.