Sour - Beer, Wine, Mead, & Cider Brewing Discussion Community.

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Sour or acidic flavor in beer is nearly always caused by bacterial infection.

There are two major types of bacteria used for souring beer. Lactic acid gives a smooth sourness that can be reminiscent of yogurt. Acetic acid gives a sharper, tangier bitterness. See the individual entries for each type of acid for more information.