Délestage – (‘dehl-luh-STAJ’) aka “rack and return” (though the French sounds much more refined and romantic, as usual.) refers to the practice of repeatedly draining fermenting red wine off of its skins through a screen that traps some portion of the seeds, then returning the drained-off juice to continue fermenting on the skins, but minus the seeds entrapped in the draining process. Fewer seeds = lower seed-to-juice ratio = less extraction of seed tannins into juice = less tannic wine.
You know that it can’t really be that simple. There are two reasons why just describing the mechanics of the operation is inadequate. First, the “rack and return” process does more than just remove seeds. Like other methods of cap management*, the process also douses the floating grape skins. Unlike some other methods of cap management, délestage generally incorporates a lot of air into the must when the juice is pumped back over the skins.
Besides stimulating their growth, oxygen discourages fermentation yeasts from producing unsavory cooked cabbage and onion-like sulfides. Oxygen also has far-reaching and often poorly-understood effects on myriad elements of wine chemistry. Tannin polymerization, for example, is influenced by oxygen in complex ways that seem, in general, to lead to softer and rounder wines In fact, the role of oxygen in winemaking is so very complex that I’m going to refrain from saying any more about it here for fear of perjuring myself. In any case, the influence of délestage on a wine can’t just be attributed to removing seeds; oxygen must play a part, too.
The second reason why délestage is more complex than its mechanical description comes from our understanding – or, rather, our lack of understanding – of tannins themselves. We once separated tannins into the two broad categories of seed tannins and skin tannins. Seed tannins were bad: harsh, bitter, and green. Skin tannins were better: softer and malleable. In this context, délestage makes a lot of sense. Decreased exposure to bitter seeds during fermentation should reduce harsh, bitter flavors.
For better or for worse, tannin chemists, led by Dr. Jim Harbertson at WSU, have shattered this simplistic understanding. Tannins are polymers of flavon-3-ols. According to Harbertson’s work, longer tannins are usually perceived as more astringent, yet seed tannins are about a third of the length of skin tannins, averaging ten instead of thirty units. On the other hand, seed tannins take longer to extract than skin tannins; even though seed tannins outweigh skin tannins in magnitude, they release more slowly. To add yet another layer of complexity, the make-up of each tannin polymer influences its sensory characteristics in addition to its sheer length. And even then tannin experts haven’t yet deciphered what happens to tannins over time to make well-aged wine seem softer and less harsh than its youthful counterpart. For more on this topic without delving into the scientific literature, try this palatable Wines and Vines article.
The upshot of how to use délestage in the face of all of this complex chemistry? Taste, taste, taste. I’m no winemaker, but isn’t this self-evident? Superb winemakers have been making superb wine for centuries before anyone ever named or knew of a flavon-3-ol. Intuitively, it makes sense that removing seeds will reduce seed-y flavors. If that makes your wine taste better, go for it. As for oxygen, even if it remains the great unknown variable, scientific uncertainty doesn’t invalidate your taste buds.
*Cap management – grape skins are pushed, parachute-like, to the top of the must by CO2 bubbles created by the fermentation process, creating a “cap” of skins that can literally float above the surface of the must. Free from the protective effects of alcohol and acid and exposed to air, this cap will rapidly submit to spoilage microorganisms if not frequently reincorporated into the must. Hence, in making red wines, the “cap” must be “managed.”
Erika Szymanski is an independent contributor to this blog. She is in no way affiliated with the sponsoring company. This blog was originally posted on her blog: The Wine-o-scope.