Several months ago we visited a Midwestern winery, tasted several of their wines, and purchased a bottle of “pink” (or blush or rose’) and placed it on our wine rack and forgot about it. A few nights ago we decided to uncork the bottle. As I placed the bottle on the counter Jill remarked on how our pink wine had developed a darker hue (our winemaker alarms were activated!). As I poured the wine into our awaiting glasses we braced ourselves for the inevitable – oxidation!
In white wines, oxidation is evident in yellowing, loss of fruity character, increased bitterness, lifeless aroma, and a has a distinctive caramel aroma (or honey smell); in pink wines, oxidation is evinced similarly and typically has a brownish hue; and in red wines, oxidation shows its ugly head when the pigments in red wine become polymerized and lose their color. White and pink wines are more susceptible to oxidation.
Whatever the cause of oxidation (and there are many) the root of the problem rests mostly on how the wine is handled – read: lack of attention to detail by the winemaker. When processing wine it is important, and there are some exceptions, to keep oxygen away from our must and wine. For the professional winemaker that means a judicious use of inert gas covers during crush and transfers. By flushing a receiving tank (during a racking or transfer) with an inert-like gas such as carbon dioxide, nitrogen or argon, the oxygen is displaced by the heavier gas and our wine is protected during this potentially oxidative situation.
As you might expect, even in the most stringent of conditions some oxygen makes its way into our must/wine. How do winemakers manage oxygen that finds its way into wine? Through the addition of sulfur-dioxide (SO2) – you see it as a message on the bottle that says “sulfites added.” SO2 or “sulfur” serves a couple of important purposes: 1) Antiseptic: at crush, it inhibits the growth of wild yeasts (although yeast can handle SO2 better than bacteria), bacteria (acetic – vinegar and lactic acid bacteria, aka: secondary fermentation), and mold; 2) Antioxidant: sulfur inhibits enzymatic action of polyphenol oxidase and laccase that leads to oxidation.
Pretty simple: SO2 cleans up our must/wine (antiseptic) and SO2 protects our wine from oxygen’s dark side (antioxidant). It is imperative for winemakers to evaluate the levels of SO2 in our wines to ensure they are properly protected. Regularly monitored using a fairly easy test, called aeration-oxidation method, gives accurate readings of how much SO2 is available or “Free” to bind with oxygen -- and informs to whether we need to make an addition!
If the Midwestern wine industry wants to be competitive and taken seriously by those outside of our region we must ensure all of our wines are properly protected against the adverse effects of oxygen.
Margallit, Y. (2004). Concepts in Wine Technology. Wine Appreciation Guild, San Francisco, CA.
Dharmadhikari, M.R., and Wilker, K.L. (2001). Micro Vinification: A practical guide to small-scale wine production. Southwest Missouri State University. Mountain Grove, MO.