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====Tannic Acid====
Tannic acid is a sub-type subclass of tannin(tannins are a subclass of polyphenols). Tannic acid is generally extracted from four sources: Chinese gallnuts, Aleppo gallnuts (these both produce ''gallic acid''), Sumac leaves, and Tara pods (produces ''quinic acid''). Forms of tannic acid can also be extracted from oak galls (seeds from oak trees) and oak bark <ref>[https://en.wikipedia.org/wiki/Tannic_acid Tannic acid. Wikipedia website. Retrieved 04/17/2017.]</ref>. Tannic acid extracts are of interest to the brewing industry because they have been found to improve flavor stability through its free radical scavenging activity, bonding of the metals involved in beer staling (specifically iron ions and perhaps copper ions), and preventing oxidative degradation of lipids that produces the aldehyde trans-2-nonenal which is responsible for the papery flavor in stale beer. Tannic acid also increases colloidal stability (clarity) by binding with the proline-rich proteins that cause chill haze. The higher molecular weight tannic acids (Chinese gallnuts or Sumac leaves) will reduce chill haze by removing these proteins, while medium molecular weight tannic acids (Allepo gallnuts) can result in a stable haze for beer styles such as Belgian Wit or German Hefeweizen <ref name="Formanek _2017">[http://dx.doi.org/10.1094/TQ-54-1-0112-01 Use of Tannic Acid in the Brewing Industry for Colloidal and Organoleptic Stability. Joseph A. Formanek and Pieter Bonte. MBAA Technical Quarterly. 2017.]</ref>.
One study showed that adding gallic acid (tannic acid from Chinese or Aleppo gallnuts) during the mash and sparge water extended the shelf life of beer by reducing off-flavors such as trans-2-nonanol, the aldehyde responsible for the papery taste in stale beer. It also bound to proteins containing thiols that when oxidized during mashing can cause filtering and amylolytic issues, and settled them out during the mashing/boiling which made filtration easier. The study determined that the tannic acid did not have an impact on the saccharification rest or the soluble protein content. It did have a very slightly negative impact on yeast attenuation, however the addition of zinc to worts that had gallic acid added resolved the attenuation issue (it is thought that the gallic acid dropped the zinc out of solution since it binds with metals, and thus negatively impacted the yeast health) <ref name="Aerts_2004">[http://www.mbaa.com/publications/tq/tqPastIssues/2004/Abstracts/0831-01.htm Evaluation of the Addition of Gallotannins to the Brewing Liquor for the Improvement of the Flavor Stability of Beer. Guido Aerts, Luc De Cooman, Gert De Rouck, Zoltan Pénzes, Annemie De Buck, Roger Mussche, and Joseph van Waesberghe. 2004.]</ref>.