I had a couple come into the winery the other day and we ventured onto the topic of reduction in wine. I mentioned the baby-poop smell of disulfides and their eyes lit up. “We JUST HAD a wine that smelled like diaper!” the lovely young woman blurted out. She clearly was thrilled that she hadn’t been hallucinating, and that there really is such a thing as poopy smelling wine.
Unfortunately for me, I am particularly sensitive to reduction in wine, and I often smell cooked corn and baby poop in wines more than others. Yuck.
Why does wine smell like canned corn? Diaper? Onions/garlic? Or eggs? Sewer or cooked cabbage?
Reduction, is the simple answer. Although there is nothing simple about reduction.
Reduction is a chemical phenomena in wine as a result of H2S being produced during fermentation and the later lack of dissolved oxygen in wine during maturation, usually in stainless steel or barrel. Reductive wines are more and more common a practice of leaving wines on the lees for extended periods of time without racking. Stainless steel fermentations and maturation also prevents oxygen pick up that can dissipate H2S compounds. Thus, over time, a wine can change from a hardly noticeable reduction of a hydrogen sulfite odor to a more serious garlic smelling wine that carries with it a terrible wine flaw; mercaptans.
Reduction is a problem created by a practice known as reductive wine making. A practice, I would argue, that every wine maker worth their salt must adhere to in order to make decent wine! This practice is simply a due diligence to prevent oxygen from contacting wine. Wine makers use all kinds of tools, chemicals, tanks and gases to keep oxygen away from wine, and sadly, reduction is often the bi-product of a diligent wine maker! However, good wine making also requires wine makers pay heed to yeast health during fermentation. Stressed yeasts produce much more H2S than happy yeasts. Proper feeding and care of fermentations profoundly decreases the amount of H2S produced during fermentations, and thus, the amount of reduction that later ensues during maturation.
Reduction can be categorized in three stages; the hydrogen sulfide stage, the disulfite stage and the mercaptan stage. However, there does not appear to be a linear progression of these stages or enough real research of these phases to completely understand what is going on during maturation. The problem with reductive wines is that they change over time, and mercaptans are often the end result. No amount of breathing or decanting can remove mercaptans from wine. The garlic smell translates into a very bitter finish in aged wines.
How do we fix reductive wine?
In the earliest stages of reduction, early racking off of the lees with plenty of O2 pick up can remove any H2S in wines. Micro-oxing in stainless tanks is all the rage to compensate for reduction during ferments and maturation. The best solution is for wine makers to use their most important tool; their nose and a long spoon.
The second and third stages of reduction require a nasty regime of adding copper sulfate to wines to break up thiols created by disulfides. Mercaptans, the end result of deeply neglected reduction, can only be removed through very expensive procedures that are often a temporary fix; the sensory factors return over time.
Like most aspects of good wine making, I believe that prevention is the best approach to reduction. I have yet to use copper sulfates in wines, although it can be applied in small amounts with very careful science to improve reductive wines successfully without posing a health risk.
So what does this mean for consumers?
I had a renown wine critic once tell me that he doesn’t care about reduction in wine, “It just blows off”, he said. He also rates wines without giving much heed to the reductive quality of the wine. This attitude is an ugly bedfellow to the same tolerance of Brett in wines, I would argue. Anytime a characteristic of a wine is an attribute of a changeable factor, the quality of the wine over time cannot be vouched for! Reduction is one of these factors.
Buyers beware! If a wine is reductive when it is young, it may remain exactly as it is over time and blow off any minor reduced odors through decanting or swirling in the glass. Or it may change into something much nastier that affects the aroma and flavor of the wine. The take home on reductive wines is that there are no guarantees that a reduced wine will improve with age. If you are drinking it young, fine. But do not purchase wines to cellar if it presents signs of reduction now.