4-Vinyl Guaiacol (4VG) is a member of a group of aromatic, monomeric phenols that includes vanillin and is widely used as a flavoring agent in the food industry. 4VG can be found naturally in most beers (especially ales), but usually well below threshold level. However, 4VG is present in weissbiers (wheat beers), rauchbiers (smoked beers), and some specialty Belgian beers in notable concentrations, generally imparting desirable spicy, pungent, clove-like notes. At higher concentrations and under certain conditions, however, it may present as a medicinal, off-flavor note.
4VG is produced by enzymatic or thermal decomposition of ferulic acid (a hydroxycinnamic acid), found in the husk of barley malt. To a more limited extent, it may be derived from release of the ferulic acid precursor found in wheat malts. With a low flavor threshold of detection at about 200 parts per billion, 4VG can exert a large influence on the flavor of beer. The main production of the compound is yeast strain specific (requiring a specific gene originally called POF for phenolic off-flavor and now renamed PAD1+) but also depends upon other process factors involved in malting and in the brewhouse. Full details of the generation of 4VG have only fairly recently been investigated by Belgian malting and brewing science researchers, who reached the conclusion that the brewer may have more control than once thought over its production. By varying mashing conditions to release more or less of its precursor, ferulic acid, the desired amount of spicy, clove flavor in the beer can be somewhat controlled.
4VG can also be produced by wild yeasts and some bacteria (which harbor the POF or PAD gene with variable degrees of expression). Hence, unless a specific wheat beer yeast strain or a Belgian strain has been used, the analysis of 4VG in beer can often be regarded as an indicator of contamination caused by wild yeast and bacteria in the brewery. Finally, because 4VG breakdown is related to vanilla flavor production, it is now being suggested that the clove-like aroma in fresh specialty beers such as wheat beers and top-fermented Belgian-style ales may shift to sweeter, more vanilla-like flavor impressions as these beers age.