Growing & Winemaking


Oak Adjuncts in Red Ferments

September 2010
by Peter Mitham

The glamor shots (such as they are in the wine craft) showing cellars with row upon row of barrels convey to consumers the romantic notion of élevage, a French term that literally means the elevation or upbringing of wine. The role oak plays in the final sensory experience of the drink seems inextricable from the use of barrels. The toast, the tannins from the wood and the dynamic interaction with the environment that oak allows all contribute to the experience of the wine through the eyes, nose and palate of the drinker.

Many winemakers are getting a jump on the barrel, however, by using various oak adjuncts (chips, shavings or powder) during red wine fermentation. One of them, Alison Crowe of Napa’s Plata Wine Partners, describes these as non-coopered oak, a nod to both the quality of the best available adjuncts and their influence on élevage.

While some winemakers use oak adjuncts to stabilize color early on, oak products are more commonly, and often with greater scientific justification, helpful in rectifying flavors prior to aging.

“The most important thing we’re trying to do is stabilize the color. One of the additional benefits is it can help reduce or eliminate any vegetal character if the grapes came with it from the vineyard,” Mike Robustelli, winemaker at McManis Family Vineyards in Ripon, Calif., says of oak used in red wine ferments.

McManis typically adds shavings to the receiving hopper. Red ferments at McManis typically run five to seven days. Shavings have a greater surface area per pound than chips, and while the must doesn’t necessarily exhibit a strong hint of oak when fermentation is through, its character is better defined, Robustelli says.

“What we’re really trying to do is make as homogenous a mixture as possible, because if the juice or the skins aren’t in contact with the chips, then they don’t have a chance to react,” Robustelli explains. “We want to avoid having a big cluster of chips in one area of the tank and no chips in other portions.”

Tannins and the question of color

Winemakers ascribe many benefits to oak added during the fermentation of red wines, from color stabilization to improved sensory characteristics. But the chemistry of oak tannins counters some of the popular assumptions.

Wine tannins fall into two classes. Condensed tannins, found in the skins and seeds of grapes, contribute astringency to wine. Hydrolyzable tannins, found in oak, consist of a sugar and several phenolic acids linked by ester bonds. These bonds break down easily under acidic conditions, limiting their influence after extraction from the oak.

The concentration of hydrolyzable tannins in a finished wine amounts to about seven to 20 milligrams per liter, explains Dr. James Harbertson, a researcher and extension enologist with Washington State University, Prosser. Condensed tannins, by contrast, range from 50 to 1,900 milligrams per liter.

Harbertson says the evidence suggests that condensed tannins are also more important than oak-derived tannins in stabilizing color. “The ability of hydrolyzable tannins to help stabilize color like the condensed tannins from grapes is also greatly exaggerated,” he says.

While oak contributes furfural, a compound that reacts with anthocyanins to make what he terms a “polymeric pigment,” it occurs at far lower concentrations than anthocyanins—50 to 200 milligrams per liter vs. 100 to 1,000 milligrams per liter. Moreover, low alcohol levels in the must may limit pigment formation. Several papers indicate that oak wood extract actually increases the loss of anthocyanins, Harbertson adds, contributing to his own hunch that oak tannins have a limited effect on color.

“My best guess would probably be that if oak chips were added at the early stages of fermentation, we would observe a loss of wine color and formation of some polymeric pigments that would probably not be much different from the control (in a lab test),” he says. “There could possibly be some changes to the wine aroma that would be positive, but pigments and tannins are not aroma compounds so this is a separate effect.”




The toast on the shavings reflects the type of grape pressed and the wine McManis aims to achieve. “Typically, the lighter, fruitier wines would see lighter toast levels. So, say our Pinot Noir would use a medium toast, and the heavier wines would use a darker toast,” Robustelli says. “Petite Sirah or Cabernet would see heavy toast or a combination of medium toast plus and heavy toast.”

He’s opted against untoasted oak adjuncts, though some claim a growing following for them. Toasting tames the raw oak flavors that might otherwise be transferred to a wine. Unlike stems and other woody material that most winemakers don’t want crushed with the grapes, toasted oak is primed to release compounds that give definition and complexity to the wine. “My concern would be, using untoasted chips, that you’d get a green, woody, resinous character,” Robustelli says, shying from the prospect.

Dave Nagengast, winemaker at Scheid Vineyards in Greenfield, Calif., shares many of Robustelli’s objectives in using oak adjuncts. While he hasn’t done enough trials to document color stabilization, he believes it happens. But he knows the overall sensory qualities of Scheid’s wines improve.

“Start getting some oak impact early on, and it helps with the mouthfeel of the wine down the line. And actually, the overall impression longer term -- if it gets started with the fermentation, it just kind of builds from there,” he says.

Nagengast uses shavings at a rate of about 3 to 4 pounds per ton of grapes. The toast is light, with the oak from the U.S., France or Hungary. Nagengast says he has also used dust, but at a lower rat e. The control over the process, and the quicker extraction during fermentation, are advantages of using adjuncts.

While oak barrels are making a bit of a comeback as fermentors, winemakers know that the engineering and design of stainless steel tanks often offer better temperature control and management of the cap. Oak adjuncts in steel or plastic tanks introduce an oak element early under circumstances that are more controlled. Nagengast says Scheid complements its use of oak adjuncts during fermentation with adjuncts during élevage, when micro-oxygenation also comes into play to mimic the gentle aeration of wine in barrels.

Prior to working at Scheid, Nagengast went to barrel with every red wine. That approach just isn’t possible at Scheid, where the capacity is 6.5 million gallons per year. “When you’re looking at a 132,000-gallon tank of wine, to put that into barrels…it’s almost ridiculous,” he says of the work that would be required to achieve the effect of barrel aging.

Moreover, most of Scheid’s wine is sold in bulk, which requires the efficient, economical production of an attractive blending component. “It’s a different perspective than when you’re just looking for one lot of wine that’s going to be a finished wine,” he says.

Joshua Maloney, red winemaker at Chateau Ste. Michelle in Washington state, uses oak chips at fermentation to eliminate green characters and soften tannins. The majority of ferments, about 60%, use inch-long chips at a rate of about 3 to 4 pounds per ton, while special lots will see quarter-inch chips. He may add a double portion -- and in extreme cases, a pound of oak dust -- where green characters are a concern.

He’s skeptical of the role oak at fermentation plays in stabilizing color. “It’s not really doing what we say it’s doing,” he says. He believes oak is more significant in masking green characters and bringing forward favorable phenolics. Oak doesn’t get rid of green characters so much as mask them, he explains.

Some winemakers will add tannins to correct a green wine, but Maloney feels oak does a better job because of its biochemistry. His own experience fermenting fruit from the same block with and without oak chips underscores his argument. “The one that we do the oak fermentation with is always more fruity and less vegetal than the one where we omit the oak chips,” he says.

Oak chips also round out the wine, softening tannins and polishing the mouthfeel. “The one with the oak is richer, it’s sweeter -- not sugar sweeter, just rounder sweeter -- and the tannins seem to be better integrated. The one without, it’s missing a little bit of extract, and the tannins are grainy in comparison.”

Special cases are when the green character of a wine is pronounced, prompting the addition of oak powder. Red wines typically spend about seven days on skins, but if there’s a whiff of vegetal aromas as the cap rises (usually on the second day), Maloney might opt to pare a day off the skin time and toss a pound of oak dust into the fermentor.

He adds that oak during fermentation doesn’t necessarily affect barrel treatment afterwards. The barrel’s oak imparts a separate character to the wine, partly due to Chateau Ste. Michelle’s practice of malolactic fermentation in the barrel.

“I still think the quality of oak that we get out of the barrel is greater than the integration and quality of the oak that we get from the chip itself,” Maloney says. “But that’s largely a stylistic choice. I don’t think you can really say that one is good and one is bad.”

Our Northwest correspondent Peter Mitham is a freelance agriculture writer based in Vancouver, B.C. Look for his weekly dispatches at Headlines. Contact him through


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