Isovaleric Acid
Isovaleric Acid, also known as 3-Methylbutanoic acid, is an organic compound with the formula (CH3)2CHCH2CO2H. The flavor and aroma are often described as rancid Parmesan, or foot odor. it is not to be confused with Butyric Acid.
Production in Beer and Wine
Brettanomyces can create isovaleric acid [1]. The compound generally takes a few months to produce in beer by Brettanomyces. Brettanomyces breaks down leucine present in beer into isovaleric acid (controversial, but generally accepted) [2][3].
Isovaleric acid can also be produced by a bacteria that lives naturally on human skin and is responsible for foot odor called Staphylococcus epidermidis. It does so by degrading leucine, an amino acid present in sweat [4]. Leucine is also present in beer [5].
Other bacteria, including species and strains of Streptococcus (more so) Lactobacillus (less so) can produce various amounts of isovaleric acid from leucine, as well as other compounds from other carboxylic acids. Lactobacillus is not capable of producing isovaleric acid without the presence of an alpha-keto acid, which is produced by Streptococcus thermophilus, so the presence of S. thermophilus or another alpha-keto acid producing microorganism is required for Lactobacillus to produce isovaleric acid (as well as a range of other acids). [6]. This may be the reason that sour mashes often have a rancid cheese off flavor (although this may also be at least partially due to Butyric Acid production during Sour Mashing).
Isovaleric acid can also be produced by the oxidation of hops [7][8].
Metabolic Breakdown
Brettanomyces can break down isovaleric acid into an ester called ethyl isovalerate. This ester is described as fruity, sweet, berry-like with a ripe, pulpy fruit nuance [9][10][11]. The rate of metabolic breakdown of isovaleric acid into ethyl isovalerate has not been researched, as far as the authors of this wiki know. See also Brettanomyces ester production.
References
- ↑ Wikipedia article
- ↑ Botha, Janita J. Sensory, chemical and consumer analysis of Brettanomyces spoilage in South African wines. March 2010. Pg 2, 13, 17, 18
- ↑ Oelofse, Adriaan. Investigating the role of Brettanomyces and Dekkera during winemaking. December 2008.
- ↑ Ara K, Hama M, Akiba S, Koike K, Okisaka K, Hagura T, Kamiya T, Tomita F. Can J Microbiol. 2006 Apr.
- ↑ Hall, Nutfield, Redhill, Surrey. Amino Acid Esters in Beer. Brewing Research Foundation. July 14, 1980.
- ↑ Helinck, Le Bars, Moreau, and Yvon. Ability of thermophilic Lactic Acid Bacteria To Produce Aroma Compounds from Amino Acids.
- ↑ Green, C. P. The Volatile Water-Soluble Fraction Of Hop Oil. Aug 24, 1909.
- ↑ Oliver, Garret. The Oxford Companion to Beer. 2001. Pg 498.
- ↑ Fenaroli's Handbook of Flavor Ingredients, Fifth Edition. George A. Burdock. CRC Press, Dec 3, 2004. Pg 587.
- ↑ 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.
- ↑ Impact of Brettanomyces on Wine. Presentation by Lucy Joseph of UC Davis. Retrieved 08/15/2015.