Ezekiel Warren, Misha Kwasniewski,* and Ryan Elias
*The Pennsylvania State University, Rodney A. Erickson Food Science Building, State College, PA, 16803 (mtk5407@psu.edu)

During wine aging, especially in barrel, small amounts of oxygen absorption cause cascading oxidation reactions, allowing tannin elongation. The reaction that causes this is the hydroxyl radical-mediated oxidation of ethanol in wine to acetaldehyde, which elongates polyphenols by adding an ethyl bridge between them. This elongation can positively affect the flavor and mouthfeel of a wine. While the importance of these reactions has been demonstrated, no method for catheterizing intact elongation products in wine exists. Additionally, all commercially used methods for inducing elongation rely on passively or actively inducing oxygen ingress rather than direct manipulation of acetaldehyde. Previous work demonstrated that direct addition of high levels of acetaldehyde acts to deplete catechin monomers by causing elongation. However, there has been no further optimization of the system or characterization of the products created. We developed an LC/MS method to measure products of the reaction using a transition of 605 to 289 m/z, which is the mass to charge of two catechins attached with an ethyl bridge and appears both in dimers (two catechins with an ethyl bridge) and other longer polymers that can be separated chromatographically. When adding exogenous acetaldehyde at low, high, and high divided into five doses (100, 500 and 100 ng/mL × five) to a model wine solution after 18 days, the catechin product increased 2.5- and 11-fold in the low and high doses, respectively, while the control had no detectable ethyl-bridged catechin. The rates of creation of the catechin product varied between the different dose concentrations and the sequential additions. Having a method for product characterization will allow further optimization of dose rates so direct acetaldehyde addition becomes an easy tool for winemakers looking to directly and predictably induce phenolic elongation.

Funding Support: Pennsylvania Wine Marketing and Research Board