By: Marlena Sheridan
Dr. Ryan Elias’s Lab
Acetaldehyde is a compound found in wine that has a profound effect on color stability and astringency. Acetaldehyde reacts directly with red wine tannins and anthocyanins to form polymeric pigments and modified tannins. Denise has already provided a great review of polymeric pigment formation. Here, I’ll be focusing on the reactions involving acetaldehyde and research we’ve completed on the topic.
Acetaldehyde reacts with tannins and anthocyanins to form irreversible, covalent bridges. When these reactions are between tannins, they can alter the structure so that its shape and activity are changed. This affects wine astringency, a mechanism based on the interaction of tannins and salivary proteins. Modified tannins, including acetaldehyde-bridged tannins, have been shown to have lower astringency because of their structural changes (Gambuti 2013). A model of these reactions is shown in Figure 1. These changes contribute to the shift from drying or puckering mouthfeel to a more velvety mouthfeel in aged wines.
Similar reactions take place between anthocyanins and tannins as well as between anthocyanins themselves. These reactions form polymeric pigments: pyranoanthocyanins and vitisins. A model for these reactions is shown in Figure 2. As Denise has covered, these polymeric pigments have increased stability to sulfite bleaching and pH changes compared to monomeric anthocyanins.
As has hopefully been made clear, using these reactions of acetaldehyde with tannins and anthocyanins is an important tool for winemakers. Winemakers can use several techniques to get the benefits of acetaldehyde on pigment and tannin structure. These use oxygen incorporation to form acetaldehyde through a series of metal-catalyzed reactions (Danilewicz 2003). Along this pathway, there is the possibility to form detrimental oxidation products instead of the desired acetaldehyde …