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Sour beer is beer with an intentionally sour taste. In traditionally produced sour beer, the acidic character results from spontaneous, mixed fermentation where different bacteria and yeast species participate. These complex fermentations take years to complete and can be difficult to control. Owing to the increasing interest in sour beer and challenges related to commercial sour beer brewing, alternative production methods are being explored. In the current paper, pre‐fermentation with lactic acid bacteria (LAB) was investigated as a timesaving and controllable strategy for the production of sour beer. Four beers were produced with either biological or chemical acidification of wort, and a reference beer was produced with no acidification. Volatile compounds and organic acids were analysed by headspace gas chromatography and high‐performance liquid chromatography to explore any contribution from LAB to the composition of beer. Finally, descriptive sensory analysis was performed to evaluate the sensory contribution from LAB. A significant effect was observed from LAB pre‐fermentation, with respect to both volatile compounds (e.g. reduced production of 2‐methyl‐1‐butanol) and organic acids (e.g. production of acetic acid). Biological acidification by LAB pre‐fermentation had a significant impact on the sensory character of beer. This sensory impact did, however, not surpass that obtained by chemical acidification, as few significant differences were found between biologically and chemically acidified beers. © 2019 The Institute of Brewing & Distilling [ABSTRACT FROM AUTHOR]