The well-known off-flavors are earthy flavor from water, staling flavor such as cardboard and aging flavor which might be involved in mashing and boiling process, hydrogen sulfide during the fermentation process, vicinal diketones during the conditioning process and light-struck character at the market.
Off-flavor in beer including:
*Acetaldehyde (green apple, rotten apple): Acetaldehyde is a naturally occurring chemical produced by yeast during fermentation. It is usually converted into Ethanol alcohol
*Butyric acid (baby vomit): Commonly produced by a bacterial infection developed during brewing, butyric acid can also arise from poor sanitation during packaging
*Diacetyl (buttered popcorn, rancid butter): Caused by the presence of polysaccharides (dextrins) in the beer that are not fermentable by the yeast. Medium length proteins also contribute to palate roundness
*Dimethyl sulfide (aka DMS; canned corn, cabbage): S-methyl methionine (SMM) is created during the malting process of grain and is later converted to DMS when heated
*Hydrogen sulfide (rotten eggs): Formed by amino acids methionine and cysteine in the malt and by certain yeast strains and bacteria, notably Zymononas, Pectinatus, and Megasphaera. Also formed by yeast autolysis
*Mercaptan (rotten vegetables, skunk): Light will degrade hop iso-alpha acids which then combine with sulphur compounds in the beer to produce 3-methyl-2-butene-1-thiol, or prenyl mercaptan. Other sulphur compounds also contribute to the overall lightstruck character
*Metallic (metal, blood): the most common source of metallic off-flavors in beer is contact with metal components in the brewery
*Oxidation (cardboard): Oxidation of beer and the alcohol components into trans-2-nonenal and other aldehydes
Off flavor in beer
