Changes

Phenols such as 4-vinylphenol (4VP, barnyard, medicinal) and 4-vinylguaiacol (4-VG, clove) can be produced in beer by the decarboxylation of hydoxycinnamic acids, which are found in malt. While both ''Saccharomyces'' and ''Brettanomyces'' strains are capable of converting hydroxycinnamic acids to their vinyl derivatives, ''Brettanomyces'' is also able to reduce these vinyl derivatives to ethyl derivatives. These vinyl derivatives have similar tastes to the ethyl derivatives but have lower flavor thresholds. Levels of all compounds produced vary depending on species and strain of ''Brett''.

| 4-vinylphenol Vinylphenol <ref name="Doss">[http://www.ahaconference.org/wp-content/uploads/presentations/2008/GregDoss_BrettBrewing.pdf Doss, Greg]. Brettanomyces:

fermentations with respect to time. Presentation at 2008 NHC. pg 12.</ref> <ref name="Yakobson_Michigan">[http://www.mbaa.com/districts/michigan/events/Documents/2011_01_14BrettanomycesBrewing.pdf Yakobson, Chad]. Brettanomyces in Brewing the horse the goat and the barnyard. 1/14/2011</ref> (Barnyard, Medicinal, Band-aid, Plastic) || Vinyl phenol || p-Coumaric Acid || Odor Strength "High" 0.2 ppm (flavor; in beer) <ref name="goodscents_4VP">[http://www.thegoodscentscompanyscielo.combr/data/rw1005801scielo.html The Good Scents Company. php?pid=S1516-89132013000600018&script=sci_arttext Determination of 4-vinylgaiacol and 4-Vinylphenolvinylphenol in top-fermented wheat beers by isocratic high performance liquid chromatography with ultraviolet detector. Mingguang Zhu; Yunqian Cui. Retrieved 08/18/2015Dec 2013.]</ref> || C₈H₈O <ref name="goodscents_4VP">[http://www.thegoodscentscompany.com/data/rw1005801.html The Good Scents Company. 4-Vinylphenol. Retrieved 08/18/2015.]</ref> || Production level is different across species/strains of ''Brett'' <ref name="Oelofse">[http://www.sciencedirect.com/science/article/pii/S0740002008002050 Molecular identification of Brettanomyces bruxellensis strains isolated from red wines and volatile phenol production. A. Oelofse, A. Lonvaud-Funel, M. du Toit. 2009.]</ref>.

| 4-vinylguaiacol Vinylguaiacol <ref name="Doss"></ref><ref name="Yakobson_Michigan"></ref> (Clove) || Vinyl phenol || Ferulic Acid || Odor Strength "High" 0.3 ppm (flavor; in beer) <ref>[http://www.aroxa.com/beer/beer-flavour-standard/4-vinyl-guaiacol/ Aroxa Website. 4-Vinylguaiacol. Retrieved 08/19/2015.]</ref> || Also known as 2-methoxy-4-vinyl phenol <ref name="goodscents_4VG">[http://www.thegoodscentscompany.com/data/rw1005101.html The Good Scents Company. 2-methoxy-4-vinyl phenol. Retrieved 08/18/2015.]</ref> || C₉H₁₀O₂ <ref name="goodscents_4VG"></ref> || Also known as 2-methoxy-4-vinyl phenol <ref name="goodscents_4VG"></ref>. Produced by some strains of ''S. cerevisiae'' <ref>[http://pubs.acs.org/doi/abs/10.1021/jf0346556 Ferulic Acid Release and 4-Vinylguaiacol Formation during Brewing and Fermentation:  Indications for Feruloyl Esterase Activity in Saccharomyces cerevisiae. Stefan Coghe, Koen Benoot, Filip Delvaux, Bart Vanderhaegen, and Freddy R. Delvaux. 2004.]</ref>. Some ''Brett'' species/strains may also be able to produce this compound in at varying levels <ref name="Joseph"></ref><ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6968.1995.tb07374.x/abstract The biotransformation of simple phenolic compounds by Brettanomyces anomalus. Duncan A.N. Edlin1, Arjan Narbad, J. Richard Dickinson1 andDavid Lloyd. 2006.]</ref><ref name="Oelofse"></ref>.

| 4-ethylphenol Ethylphenol <ref name="Doss"></ref><ref name="Yakobson_Michigan"></ref> (Barnyard, Spicy, Smoky, Medicinal, Band-Aid <ref>[http://www.aroxa.com/wine/wine-flavour-standard/4-ethyl-phenol/ Aroxa Website. 4-Ethyl Phenol. Retrieved 08/19/2015.]</ref>) || Ethyl phenol || 4-vinylphenol || 0.3 ppm (odor; in beer) <ref name="Maarse">[https://books.google.com/books?id=_OvXjhLUz-oC&pg=PA513&lpg=PA513&dq=4-ethylphenol+odor+threshold&source=bl&ots=fzhA9yvvrJ&sig=K0QykyRqj9TnezG1Mih4gLru1ZE&hl=en&sa=X&ved=0CC4Q6AEwAmoVChMI77DfhNi1xwIV0jqICh1zVgQ8#v=onepage&q=4-ethylphenol%20odor%20threshold&f=false Volatile Compounds in Foods and Beverages. Henk Maarse. CRC Press, Mar 29, 1991. Pg 514, 515.]</ref> || C₈H₁₀O <ref name="pubchem_4EP">[http://pubchem.ncbi.nlm.nih.gov/compound/4-ethylphenol PubChem Website. 4-Ethylphenol. Retrieved 08/19/2015.]</ref> || Also known as 1-Ethyl-4-hydroxybenzene and P-Ethylphenol <ref name="pubchem_4EP"></ref>.

| 4-ethylguaiacol Ethylguaiacol <ref name="Doss"></ref><ref name="Yakobson_Michigan"></ref> (Smokey, Spicy, Clove<ref>[http://www.aroxa.com/discovery/discovery-standard/4-ethyl-guaiacol Aroxa Website. 4-Ethyl guaiacol. Retrieved 08/19/2015.]</ref>) || Ethyl phenol || 4-vinylguaiacol || || |||-| 4-Ethylcatechol 0.13 ppm (odor; in beer) <ref name="DossMaarse"></ref> || C₉H₁₂O₂<ref name="Yakobson_Michiganpubchem_4EG">[http://pubchem.ncbi.nlm.nih.gov/compound/62465 PubChem Website. 4-Ethyl-2-methoxyphenol. Retrieved 08/19/2015.]</ref> (Band‐aide, Medicinal, Barnyard) || Also known as 4-Ethyl phenol || 4-Vinylcatechol || || ||2-methoxyphenol <ref name="pubchem_4EG"></ref>.