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Carl Hudson
January 16, 2019 | Wine "Fun" Facts | Carl Hudson

Oak Barrels & Oak Alternatives

Over two years ago, now, a four-part series of Carl’s Corners were posted covering many details of the use of oak barrels in wine production and aging.  Since much Texas wine, especially reds, from the 2018 vintage is resting comfortably in oak barrels this winter, it seems a good time for an update on oak and wine. 

Oak can have significant impact on wine, influencing color, flavor, tannin profile, and even texture.  Oak treatment normally occurs when wine is fermented and/or aged in barrels, but increasingly oak alternatives, chips, pellets, staves, etc., are used to add oak influence to wine in other vessels, i.e., stainless steel tanks.  Oak barrels influence the qualities of wine in several ways:  1) allows slow evaporation which concentrates flavor components, 2) porosity allows low level exposure to oxygen (in the air) which mellows tannins and modifies flavor characteristics, and 3) introduces wood-based flavors, like vanilla, spices, smoke & tobacco notes.  There are specific oak tannins that help to protect wine from oxidation, thus making oak barrels a very useful vessel for aging. 

Wine barrels are produced from several species of white oak, typically harvested from 75-125 years old trees.  Managing forests of these trees is big business in many regions of the world, especially parts of France, eastern Europe, several east/central U.S. states, including AR, MO, KY, IN, PA, MN, and WI, and even out west in Oregon or up north in Canada.  Oak wine barrels are expensive, ranging from $350-550 for lower end American oak to $800-1,300 for French & European oak.  This adds about $1.50-4.50 per bottle cost to the wine.  Higher-end barrels are produced using special procedures and carefully selected oak staves for top wineries around the world.  Part of the cost of these barrels is related to the fact that only 2-4 barrels can be produced from a single white oak tree. 

American white oak is characterized by relatively fast growth, wider grain, and less wood tannin which imparts stronger flavor characteristics of vanilla, spice, and caramel at a faster rate.  French oak, with its tight grain, imparts more subtle characteristics of delicate, sweet-scented vanilla, softer spice notes, and a bit more tannin.  The insides of barrels are toasted over flame, radiant heaters, or with steam to impart various flavors to the wine.  Lighter toasting imparts more oak flavors and wood tannins.  Heavier toasting creates more roasted, smoky aromas and flavors.  Toasting also creates vanillin and other spice flavors.  Many winemakers utilize barrels from different sources with different levels of toast to enhance the complexity of their finished wines.  The term “winemaker’s spice rack” relates to the way oak barrels are used in a winery to flavor different wines and blends.

Oak barrels are slightly porous, allowing 1) slow evaporation of liquid and 2) low level exposure to oxygen (from the air).  Controlled air exposure helps to mellow & mature a wine, but evaporation reduces the amount of wine available - as much as 4-6 gallons of wine can be lost through evaporation each year from a typical 59 gallon (225 Liter) oak barrel.  As liquid is lost, the resulting air space can dramatically increase oxygen exposure to wine, and perhaps cause premature oxidation or spoilage.  For this reason, winemakers constantly check their barrels and refill (a procedure called “topping”) with more wine during the aging process.  Just think, a large winery that produces 100 barrels of cabernet sauvignon per vintage (2,500 gal/1041 cs) will need about 475 gal of topping wine (equal to 198 cs) in order to age the wine for 18 months before bottling and release! 

Oak barrels are most often used for aging wines after fermentation (usually in SS tanks), but fermentation in barrels is also a time-honored process.  Although it may seem counter-intuitive, aging wine in oak introduces more oak flavors than will result in wine fermented in oak.  After fermentation in oak barrels, dead yeast cells, or lees, are separated as the wine is racked to another container (tank or barrel).  When these lees are removed, they take with them a measurable amount of the oak character that resulted from fermentation in oak.  On the other hand, when a finished wine is placed into a barrel for aging, it is usually clear of most lees, thus the full impact of oak character ends up in the wine. 

New barrels impart far more flavor into wine than a used barrel.  Typically, a new barrel delivers up 50-70% of its flavoring components during the first use.  Second use can impart 20-30% flavoring while third and fourth use impart 10-20% and 5-10%, respectively.  Over time oak flavoring properties are "leached" out of the barrel while layers of natural deposits build up to limit oxygen transport through the wood, an important part of the wine maturation process.  Thus, the selective use of different types, styles and sources of oak barrels, as well as new vs. older barrels, provides the winemaker a wide range of flavoring options. 


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