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'' (only by "phenolic off flavor positive/POF+" strains) and ''Brettanomyces'' strains are have varying capabilities based on strain of converting hydroxycinnamic acids to their vinyl derivatives <ref name="Lentz">[http://www.mdpi.com/2304-8158/4/4/581/htm Analysis of Growth Inhibition and Metabolism of Hydroxycinnamic Acids by Brewing and Spoilage Strains of Brettanomyces Yeast. Michael Lentz and Chad Harris. 2015.]</ref>, ''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 ''Brettanomyces''.

'''p-Coumaric Acid''' (found in malt and other ingredients) converts to '''4-Vinylphenol''' by both POF+ strains of ''Saccharomyces'' and ''Brettanomyces'', which converts to '''4-Ethylphenol''' by ''Brettanomyces''.

'''Ferulic Acid''' (found in malt and other ingredients) converts to '''4-Vinylguaiacol''' by both POF+ strains of ''Saccharomyces'' and ''Brettanomyces'', which converts to '''4-Ethylguaiacol''' by ''Brettanomyces''.

'''Caffeic Acid ''' (found in malt and other ingredients) converts to '''4-Vinylcatechol''' by both POF+ strains of ''Saccharomyces'' and ''Brettanomyces'', which converts to '''4-Ethylcatechol''' by ''Brettanomyces''.