Technique

White Wine Skin Contact

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Rules are made to be broken, and nowhere is that subversive adage more true than in home winemaking. Today’s proposed violation takes on one of the dominant conventions of modern white winemaking: no skin contact.

This rule is the bedrock distinction between white and red winemaking, right? Reds are born to suck treasures out of the skins during fermentation, while whites shed their skins ASAP. But it hasn’t always been this way, and it isn’t the way some very fine contemporary white wines are made, and it doesn’t have to be that way in your garage, either.

A short period of carefully controlled and monitored maceration for certain white wines works like a cold soak on Pinot Noir, pulling out more aromatic and textural goodies and goodie precursors before the heat and ethanol kick in. Of course, as with breaking any other rule, there can be a downside, in this case particularly the extraction of phenolics that can, in excess quantities, make delicate whites coarse and bitter.

It’s an edgy technique. It doesn’t always work exactly as planned. Some influential people hate it. Reason enough that you should definitely try it in your home winery.

Skin Phobia

Back in the mists of time, most all white wines were fermented on their skins, usually in open top fermenters, at uncontrolled temperatures, just like red wines. You can find reincarnations of the Old Way today, in the form of so-called “orange wines,” from producers in Sicily and Friuli, California and that bastion of traditionalism, Brooklyn. White wines fermented in red wine fashion pull enough pigment out of the skins to develop earthy colors, and the inevitable oxygenation of open-top fermentation adds to the orangeness. Wines made this way also tend to suffer no sulfur additions and skip filtration, so what ends up in your glass may be a tad cloudy, redolent of Sherry vapors, and, um, interesting. However, that’s not what this article is all about.

Since World War II, the worldwide wine industry has rewritten the white wine playbook. Juice and pulp are separated from the skins right at the start. Fermentation is done in neutral, closed stainless steel at steady, cool temperatures. Reductive winemaking keeps oxygen at bay, fining and sterile filtration make the wines crystal clear and shelf stable, and early bottling ensures fresh, fruity, bright wines. Adopting these protocols has exponentially improved the quality of white wines around the world, both at the high end and throughout the broad mass market. In this hugely successful recipe, avoiding skin contact is a core component.

“The goals for white wines differ from red wine production in several respects. Generally little to no skin contact is desired. This is because the principle flavor and aroma compounds are located in the pulp of the grape with the skin providing little other than bitterness and astringency. Many white wine styles are designed to be consumed relatively young (less than five years of age), which is insufficient time to allow polymerization and softening of the phenolic content. In addition to bitterness, phenolic compounds lead to off-color production under oxidizing conditions. This color change is generally undesirable in white wines . . .”

“Skin contact refers to the length of time the juice is left in contact with the skins and seeds. The longer the time of contact the greater the extraction of the components of the skins into the juice. In contrast to red wine production, the majority of the important sensory components of white grapes are in the pulp not in the skins. Since the microbial flora of the grapes is located on the skins, skin contact also increases the contact of these organisms with the juice. If the skins are separated from the juice quickly, the microbes are also separated, minimizing their numbers in the primary fermentation.”

This is how most commercial wineries approach white winemaking, and also what most home winemakers strive for. The threat of phenolic coarseness is a real one, if skin contact is done incorrectly or to excess, and if I was responsible for ten thousand gallons of wine, I’d probably play it safe myself. But the comforting advantages of skin contact avoidance have morphed into dogma, discouraging experimentation and risk-taking that can yield distinctive wines.

But in fact, a lot of commercial folks employ skin contact, even though it doesn’t get talked about much. The great white wines of Alsace, for example, routinely make use of skin contact. It is worth noting that all the big suppliers of winemaking additives carry products, mainly enzymes, explicitly geared toward skin contact extraction, which suggests there must be buyers out there somewhere. In addition, contemporary grape processing almost guarantees that a high proportion of white grapes see some skin contact. Mechanical harvesting busts up a portion of the fruit, which oozes over the other grapes for what may be a couple of hours or more before the official crushing and pressing begins. And even hand-picked, whole-cluster-pressed grapes spend an hour and a half or so in the press cycle, which means, sure enough, some skin contact.

So the question before us here is not skin contact or no skin contact, but how much skin contact, for how long, and under what conditions?

Skin Contact Basics

Step one is selecting the right grape varieties for skin contact treatment. Echoing Willie Sutton’s preference for robbing banks, because that was where the money was, skin contact delivers its biggest dividends with highly aromatic white grape varieties: Gewürztraminer, Riesling, Muscat, Viognier, Chenin Blanc, Sauvignon Blanc and aromatic hybrids like Valvin Muscat. It makes sense that grapes that have lots of aromatic punch are the ones most worth treating with the aim of getting more olfactory riches into the wine. There is no particular reason to employ skin contact for Chardonnay or other more or less neutral grape varieties; no amount of extraction will find some hidden mother lode of terpenes or pyrazines, because there isn’t one. Skin contact on neutral varieties mainly pulls out tannins, which may need to be fined away later on.

Candidate grapes for your skin contact experiments should also be fully ripe for the best results. With underripe fruit, your challenge as a winemaker is to minimize or mask green or bitter flavors, and skin contact will simply extract more of them to deal with, while adding a note of astringency to the mix. The compounds you don’t want from your skin contact tend to decrease in concentration in the grape berries as they mature. Overripe fruit is also not the best raw material for skin contact, largely because of pH issues (discussed later in this story).

Once you have the right grape variety, in the right stage of ripeness, you have to come to grips with the fact that you have very little control over what gets extracted during skin contact. You will get the good, the bad and the incidental. Some enzymes on the market may tweak the balance a bit, but there is no magic pixie dust that guarantees you will only get enchanting floral aromas and not a trace of tannin. Time on the skins will pull out some combination of all of the following:

• Aromatic compounds — especially monoterpenes and methoxypyrazines (monoterpenes tend to give off floral aromatics while methoxpyrazines create green aromas such as green bell pepper).

• Aromatic precursors, bound with something else (conjugates) but able to be liberated through fermentation

• Phenols and polyphenols

• Unsaturated lipids

• Nitrogen

• Potassium

The aromatic compounds are, of course, the magnet for the technique. Few of the key volatiles in wine aroma are found fully formed in grape skins or juice; most require fermentation to develop. But monoterpenes — linalool, geraniol — and grassy methoxypyrazines do exist in their native states and can be powerful ingredients in the aromas of a finished wine. Both of these classes of compounds are found in high concentrations in the skins of certain grape varieties.

The aromatic precursors are a bonus, providing more material for eventual transformation into volatile compounds. These include carotenoids (which can morph into rosy damascenone), cysteine conjugates (which lead to the thiols in Sauvignon Blanc), and glycoconjugates (sugar-bound potential volatiles).

Grape skins have the highest concentrations of flavonoid-type phenols and polyphenols, including tannins (and their component parts). This is what consensus winemaking warns us against, and too much can be way too much. But in balance, a dash of tannin in an otherwise flavorful white wine can add a bit of structure and some heft to the mouthfeel — something that might be considered a more “serious” white wine. Skins also contain some amount of hydroxycinnamic esters — coutaric, caftaric, and fertaric acids — which function as precursors for later volatile phenols. Boosted phenolic content may also help with ageability of white wines made with skin contact. Finally, because skin contact pulls out pigment, rosy-colored grapes — like Pinot Gris and Gewürztraminer — may bleed a little pinkish color into the wine, too.

Lipids aren’t so helpful; these fatty acids can be the basis for off flavors. The good news is their concentration in grapes declines with increasing maturity. Nitrogen from the skins adds to the available nutrients during yeast fermentation; this may be a good thing, or could contribute to a nitrogen overload if the pulp is also nitrogen-rich and the winemaker automatically dumps Di-ammonium Phosphate (DAP) into every fermentation. The extraction of additional potassium from skin contact will increase the juice pH. For most white grapes, that increase will still leave the pH in a reasonable range, but it should certainly be measured. For overripe grapes with already elevated pH, this can mean a jump to an undesirable, spoilage-prone level.

In addition, skin contact gives more opportunity for whatever microbes came in from the vineyard to make their way into the wine. Quick pressing and separation gets rid of hitchhiking flora; skin contact gives them a foothold, however brief. Skin contact with unhealthy, moldy grapes can turn into a bad lab experiment, but skin contact with healthy grapes can add to the microbial diversity of the fermentation.

Time and Temperature

Time and temperature are the two main drivers of the extractive activity during white wine skin contact. Skin contact times can vary from a short, two to four hours, aided by enzymes, to a leisurely 24 hours or even longer. Yair Margalit, wine chemist, winemaker and author of Winery Technology & Operations: A Handbook for Small Wineries and Concepts in Wine Chemistry estimates that the extraction of flavonoid phenolics doubles in about 16 hours. Winemakers are all over the map on this; there is no generic “right” answer. The timing depends on the intended style of the wine and the condition of the grapes themselves; if they are, for example, only borderline ripe, keep the contact time, if any, short.

Temperature is critical: cool grapes and juice slow down the process of extraction, heat speeds it up. Most practitioners aim for very cool grapes, down well under 60 °F (15 °C), often under 50 °F (10 °C). You can keep your grapes in the temperature sweet spot in your homewinery by making sure they were crushed cool. If you harvest your own grapes be sure to do it either early in the morning or even at night — before the heat of the day warms them up. If you are buying your grapes and can’t be at the vineyard to receive them, cool them down in a refrigerator before crushing. You may need to do some refrigeration even when harvesting your own grapes if the conditions are warm. Once the grapes are crushed be sure to keep the temperature of the must consistently cool as you would during fermentation. Stretching out the extractive activity gives more time for tasting the juice-in-progress and for cutting it off if there is too much tannin buildup. Chilled fruit also offers less opportunity for the initiation of spontaneous fermentation activity, which is not a good idea.

That last point needs underscoring: skin contact should be done before any significant amount of yeast activity kicks in. The extraction should be done by cool juice (essentially, by water), not by exploding yeast populations or in the presence of fermentation heat and rising ethanol. Unless, of course, you are aiming to make an orange wine.

The question of sulfur dioxide additions is a tricky one in a skin contact context. A winemaker might want the protection of a dose of SO2 while the grapes are just lying there oozing; but SO2 increases the rate of extraction of phenolics, which that same winemaker is trying to limit. For short-term skin contact, anything up to eight or ten hours, it probably makes sense to hold the SO2 until the grapes are pressed and the juice settled overnight.

Crushed grapes simply sitting in bins or buckets get exposed to oxygen, though a few hours of air contact right at the beginning of (actually, before) fermentation isn’t such a bad thing. For an abundance of caution, let the grapes soak under a blanket of an inert gas (like carbon dioxide) and keep them covered.

And finally, we get to the use of enzymes, which can be a complicating factor. Enzyme additions are a popular technique in commercial winemaking and are also in the toolbox of many home winemakers. (I am a low-enzyme kind of guy myself, but you may not be.) Their use can increase juice yield and aid in clarification of wine after fermentation. And specifically for skin contact situations, enzymes may be able to help free up more bound aromatic compounds and precursors.

If you do go the enzyme route with a skin contact approach, remember that not all enzymes are created equal. They all ultimately get derived from the same Aspergillus niger fungi, and all have somewhat overlapping functionality, but different products are optimized for different purposes. You would not, for example, want an enzyme especially good at extracting tannins for these types of white wine skin contact experiments. Look for the enzymes that explicitly refer to skin contact and read up on what they promise to do before opening that pouch. And keep in mind that if you have an extractive enzyme in the mix, stuff will be coming out of those skins more rapidly, so your target contact time may be shorter. (For more information about working with winemaking enzymes, read Daniel Pambianchi’s “Advanced Winemaking” column on Using Winemaking Enzymes in the February-March 2013 issue of WineMaker.)

Trials and Tasting

The fact that skin contact is a double-edged technique, capable of putting your aromatic white in overdrive or driving it into a ditch, makes it a perfect subject for split batches and multiple trials. Even if your garage isn’t a full-fledged scientific laboratory, having some kind of control available for evaluating your experiment is important; without a comparison, it’s hard to know what you learned. So rather than betting your entire harvest of Riesling on a skin contact bet, do some with skin contact and some without.

This experiment doesn’t require massive amounts of fruit. 250 pounds (~113 kg) of an aromatic grape is enough to split three ways: 1⁄3 straight to press, 1⁄3 getting six hours on the skins, 1⁄3 getting twelve hours, fermented separately with the same yeast strain and at the same temperature. That would yield three carboys of wine, which would be ready for taste comparison soon after fermentation. Down the road, you could blend it all together, or you could bottle all three separately and have comparative tastings every three months for five years.

If you overshoot on the phenolic extract, there are two possible remedies (beside blending with a less phenolic wine). Reintroducing just a pinch of residual sugar can smooth over a mildly tannic edge. For hard cases, fining agents can remove a portion of tannin, just as they do with over-extracted red wines.

Don’t rush to “fix” your wine, however; let it develop for a while. The presence of phenolics in amounts not usually found in white wines may be apparent very early on, while the fruits of all those extracted precursors can take months to develop. I have more than once had the experience of fearing I had overdone the phenolic extract, only to have the wine fill out and mature to the point where the tannin was just a mouthfeel enhancement, not a sore thumb.

Experienced home winemakers all know that making good white wines can be tougher than making good reds. The wines themselves are more delicate, so they show their warts more easily, and the conditions and equipment in your garage or basement make it hard to exercise full control of temperature, oxygen and other things. Although those factors make whites more of a challenge, it is one you should definitely take on. If you’re up for the experiment, and you can control for some of the variables, trying a little skin contact with some of your wines can be a fun way to try something new with your whites. And while you’re at it, give yourself permission to break some winemaking rules.

Pros and Cons from the Pros

Winemaker and wine educator John Buechsenstein has on his resume, among other things, several years of producing the wines of Sauvignon Republic, a label that made Sauvignon Blanc from vineyard sources on several continents. His first comment was that the only reason for skin contact with Sauvignon Blanc would be for greater juice yield.

His reason for shunning skin contact was the danger of phenolic coarseness in the wines. “There was a big fad for Chardonnay skin contact in the 1980s,” he said, “which just meant that people had to go back and fine them. It didn’t increase aromatics, just astringency and bitterness. What you gained in juice yield you lost in fining.” In the case of Sauvignon Blanc, he thinks those skins may not be as rich in aromatic goodies as Riesling or Gewürztraminer grapes.

When I reminded him that I would be writing for a home winemaking audience, he softened a bit. “If you can get chilled fruit,” he said, “and keep it down near 40 °F (4 °C), and keep it covered, you might get something good out of skin contact at home.” And he also admitted to having a fondness for the final bitter bite on the finish of good Alsatian wines.

Yair Margalit, winemaker in both Israel and Napa and the author of texts on wine chemistry and winery technology, showed this same mix of attitudes: white skin contact is a bad idea, except when it’s a good idea. “People try to do it to get aromatic material,” he said, “using an analogy with red wine extraction, and what they extract are problems.” His list included the effects of added potassium in raising wine pH, the fact that phenolic bitterness can’t be masked in whites the way it can in reds, and the likelihood of a bitter aftertaste. All in all, he argued, “you get better aromatics from free run juice and whole cluster pressing.” For Gewürztraminer in particular, he felt it already had such an aromatic load that there was no reason for more.

On the other hand, he acknowledged, trying a kind of cold soak, a few hours at cold temperature, without fermentation, might be a good idea to try. He urged anyone who gives it a shot to have a control batch without skin contact; otherwise, how do you know what caused what?

At Ravines Winery in New York’s Finger Lakes, I found my one solid fan of skin contact in owner/winemaker Morten Hallgren, who uses a portion of skin contact grapes on several of his white wines. Ironically, one of the things that convinced him that this was a good track was an accidental experiment with a batch of Gewürztraminer some years back, which, because of a production bottleneck, sat on the skins for 36 hours . . . and came out just fine. His normal practice is more like eight to twelve hours.

In the cool Finger Lakes climate, Hallgren is likely to employ a higher proportion of skin contact in warmer/riper years, less in chillier seasons. He does some contact in a tank press, simply closing the exit valves for a while, and some in open top fermenters. After going back and forth on the timing of SO2 additions, he now generally holds off until after pressing, to moderate the phenolic extraction.

Wine critics, including Eric Asimov of the New York Times, have been falling over themselves praising Ravines’ dry Rieslings from recent vintages. So the next time someone tells you that you should avoid skin contact on white wines, tell them that they need to do a little more research!

Skin Contact Checklist

• Choose an aromatic grape variety

• Do skin contact with properly ripe fruit

• For a first time trial, separate grapes into a skin contact batch and a control batch

• Crush chilled grapes and keep the must chilled throughout, well under 60 °F (15.5 °C)

• Keep crushed grapes covered and blanketed with gas while they soak

• Extractive enzymes will speed up the effects of skin contact

• Do not add yeast or encourage fermentation until after skin contact

• Taste must every few hours to monitor extraction

• Hold off SO2 additions till grapes have been pressed and juice settled overnight

• Expect skin contact wines to develop more slowly

• Treat excessive phenolic extraction with either residual sugar
or light fining