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''Secondary metabolites'' are compounds that are not essential to the life of an organism <ref>[http://en.wikipedia.org/wiki/Secondary_metabolite Wikipedia. Secondary Metabolite. Retrieved 6/2/2015.]</ref>. ''Brettanomyces'' will use a range of secondary metabolites to produce many of the fruity and funky esters, phenols, and acids that this genus of yeast has become known for. ''Brettanomyces'' has also been observed anecdotally to produce thin beer when fermented on it's own, and this has at least partially been attributed to the lack of glycerol production by ''Brettanomyces''. The lack of glycerol production has been attributed to a genetic predisposal to prefer pyruvate production over glycerol production during fermentation, and it has been speculated that this gives ''Brettanomyces'' an adaptive advantage <ref>[http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0155140 Independent Evolution of Winner Traits without Whole Genome Duplication in Dekkera Yeasts. Yi-Cheng Guo, Lin Zhang, Shao-Xing Dai, Wen-Xing Li, Jun-Juan Zheng, Gong-Hua Li, Jing-Fei Huang. 2016.]</ref><ref name="yakobson_introduction"></ref>. The major secondary metabolites of ''B. bruxellensis'' fermentation have been identified in one study as the ethyl phenols (4EP and 4EG), the alcohols isoamyl alcohol, 2-methyl-butanol, 2-ethylhexanol, phenethyl alcohol, and an ester ethyl 2-methyl butyrate. Many other compounds are considered minor secondary metabolites and are produced in varying degrees or not at all based on the strain of ''Brettanomyces'', but may still be produced in high enough concentrations to contribute to the flavor and/or aroma in beers fermented with ''Brettanomyces''. The types and amounts of flavor compounds produced by ''Brettanomyces'' cover a wide spectrum, and many factors such as species/strain, amino acid precursors, presence of oxygen, and other nutrients, play a large role in production of these compounds. In one study on ''Brettanomyces'' in wine, some strains rated as being perceived positively if the strains metabolized certain compounds slower and produced other compounds slower, indicating that the age of the fermented beverage also plays a large role in how beverages fermented with ''Brettanomyces'' are perceived <ref name="Lucy_2015" />.

| Ethyl isovalerate (fruity, sweet, berry-like with a ripe, pulpy fruit nuance, artificial grape <ref name="Fenaroli_ethylisovalerate">[https://books.google.com/books?id=15HMBQAAQBAJ&pg=PA638&lpg=PA638&dq=ethyl+valerate+threshold&source=bl&ots=avVr8PQQ_p&sig=zm81_lhLU86VJ4jBNnm4I9nnxDw&hl=en&sa=X&ved=0CDIQ6AEwBGoVChMImYrEl6usxwIVAjmICh1HGwEs#v=onepage&q=ethyl%20isovalerate%20threshold&f=false Fenaroli's Handbook of Flavor Ingredients, Fifth Edition. George A. Burdock. CRC Press, Dec 3, 2004. Pg 587.]</ref>) <ref name="Joseph"></ref><ref name="lucy_joseph"></ref><ref name="Lucy_2015" /> || [[Isovaleric Acid]] and ethanol || 30ppm (flavor) <ref name="Fenaroli_ethylisovalerate"></ref> || C₇H₁₄O₂ (same as ethyl valerate) <ref name="Fenaroli_ethylisovalerate"></ref> || Also found in pineapple, orange juice and peel oil, bilberry, blueberry, strawberry, Swiss cheese, other cheeses, cognac, rum, whiskey, sherry, grape wines, cocoa, passion fruit, mango, and mussels <ref name="Fenaroli_ethylisovalerate"></ref>. Also known as Ethyl 3-methylbutanoate <ref name="Joseph"></ref>. Commonly produced by strains Not identified as a major product of ''B. bruxxellensisbruxellensis'' , but is produced in large quantities by some strains <ref name="Lucy_2015" />.

| Ethyl valerate (Sweet, fruity, acidic, pineapple, apple, green, berry, tropical, bubblegum <ref name="Lucy_2015" /><ref name="goodscents_ethylvalerate">[http://www.thegoodscentscompany.com/data/rw1000701.html The Good Scents Company. Ethyl Valerate article. Retrieved 08/15/2015.]</ref>) <ref name="Joseph">[http://www.ajevonline.org/content/suppl/2015/07/28/66.3.379.DC1/Supplemental_Data.pdf Supplemental Data for: Joseph, C.M.L., E.A. Albino, S.E. Ebeler, and L.F. Bisson. Brettanomyces bruxellensis aroma-active compounds determined by SPME GC-MS olfactory analysis. 2015.]</ref><ref name="lucy_joseph">[http://slideplayer.com/slide/4473144/ Impact of Brettanomyces on Wine. Presentation by Lucy Joseph of UC Davis. Retrieved 08/15/2015.]</ref> || Valeric Acid (pentanoic acid) and ethanol || 1500-5000 ppm (odor) <ref name="Fenaroli_ethylvalerate">[https://books.google.com/books?id=15HMBQAAQBAJ&pg=PA638&lpg=PA638&dq=ethyl+valerate+threshold&source=bl&ots=avVr8PQQ_p&sig=zm81_lhLU86VJ4jBNnm4I9nnxDw&hl=en&sa=X&ved=0CDIQ6AEwBGoVChMImYrEl6usxwIVAjmICh1HGwEs#v=onepage&q=ethyl%20valerate%20threshold&f=false Fenaroli's Handbook of Flavor Ingredients, Fifth Edition. George A. Burdock. CRC Press, Dec 3, 2004. Pg 638.]</ref> || C₇H₁₄O₂ <ref name="goodscents_ethylvalerate"> </ref> || Valeric acid quantities found in beer are minimal (0-1 ppm) and below odor threshold <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1974.tb03598.x/pdf Organoleptic Threshold Values of Some Organic Acids in Beer. Sigmund Engan. 1973.]</ref><ref>[https://books.google.com/books?id=allg4XxlOM4C&pg=PA91&lpg=PA91&dq=valeric+acid+beer&source=bl&ots=Pfb6EL9ufV&sig=sTb3gjpv7dlQNBOmGBPuDXJegLs&hl=en&sa=X&ved=0CB4Q6AEwAGoVChMIx9Kstp6sxwIVzCqICh2r7wc3#v=onepage&q=valeric%20acid%20beer&f=false Aroma of Beer, Wine and Distilled Alcoholic Beverages. L. Nykänen, H. Suomalainen. Springer Science & Business Media, May 31, 1983.]</ref>, and is probably also the case for Ethyl valerate. Ethyl valerate is also known as ethyl pentanoate <ref name="goodscents_ethylvalerate"></ref>. Also found in apples, bananas, guava, stawberry, cheeses, rum, whiskey, cider, sherry, grape wines, cocoa, coffee, honey, and passion fruit <ref name="Fenaroli_ethylvalerate"></ref>. Not identified as a major product of ''B. bruxellensis'', but is produced in large quantities by some strains <ref name="Lucy_2015" />.

| Ethyl-2-methyl butyrate (minty, menthol, citrus, green apple) <ref name="Lucy_2015" /> || Ethanol, methanol, and butyric acid || || C₇H₁₄O₂ || Also known as ethyl 2-methylbutanoate <ref>[http://www.thegoodscentscompany.com/data/rw1004871.html "Ethyl 2-methyl butyrate". The Good Scents Company website. Retrieved 02/24/2017.]</ref>. Found in bilberry, and in many other fruits, e.g.raw and cooked apple, apricot, orange, grapefruit. Used as a fruit flavor additive <ref>[https://pubchem.ncbi.nlm.nih.gov/compound/Ethyl_2-methylbutyrate#section=Top "Ethyl 2-methylbutyrate". PubChem website. retrieved 02/24/2017.]</ref>. Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| 4-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>. Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| 4-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 || 0.13 ppm (odor; in beer) <ref name="Maarse"></ref> || C₉H₁₂O₂ <ref name="pubchem_4EG">[http://pubchem.ncbi.nlm.nih.gov/compound/62465 PubChem Website. 4-Ethyl-2-methoxyphenol. Retrieved 08/19/2015.]</ref> || Also known as 4-Ethyl-2-methoxyphenol <ref name="pubchem_4EG"></ref>. Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| 2-Ethyl-1-hexanol (fake floral, chemical, fusel oil) || Alcohol || Associated with caffeic acid, ferulic acid, tyrosine, and phenylalanine || || Produced by many strains of ''B. bruxellensis''. Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| 2-Methyl-1-butanol (oxidized/canned fruit, plastic, sulfur) || Alcohol || Associated with ferulic acid, phenylalanine, and tyrosine <ref name="Lucy_2015" />. || || Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| Isoamyl alcohol <ref name="Lucy_2015" /> || Alcohol || 3 Methylbutanal || || One of several isomers of Amyl alcohol; also known as 3-methyl-1-butanol. It is a major higher chain alcohol produced in fermentation <ref>[https://pubchem.ncbi.nlm.nih.gov/compound/3-Methyl-1-butanol "3-Methyl-1-butanol". PubChem Website. Retrieved 01/30/2017.]</ref>. Commonly produced by many strains of ''B. bruxellensis''. Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.

| Phenethyl alcohol <ref name="Lucy_2015" /> (floral, dried rose <ref>[http://www.thegoodscentscompany.com/data/rw1010052.html "Phenethyl alcohol". The Good Scents Company Website. Retrieved 01/30/2017.] </ref>) || Alcohol || || || Also known as phenethanol . Identified as a major product of ''B. bruxellensis'' <ref name="Lucy_2015" />.