Gewürztraminer Barrel Aging
Updated 04/06/2007
Barrel Aging (Source: Options with Red Wines by Peter Bell)
When a wine is stored in oak barrels a great many changes take place. Most obviously, a range of aromatic compounds is extracted by the wine. White oak, properly air-dried and toasted, contains perhaps a hundred or so compounds that are either water- or ethanol-soluble. These have effects both on the aroma and on the mouthfeel of the wine.
Also, wine in barrels is exposed to small, regular amounts of oxygen. It was assumed until recently that this was from penetration of air through the pores of the wood, but that has now been shown not to be the case. What is more likely is that the act of removing the bung in order to top up the barrels or take samples exposes the wine to small amounts of air. Oxygen is generally seen as an enemy of wine; however, controlled amounts can have a beneficial effect on the polyphenolic substances in a red wine.
Lastly, wine in barrels undergoes straightforward aging reactions, most importantly the polymerization of phenolics, with an accompanying precipitation as well as a modification of tactile sensations in the wine.
A great deal of time and effort are spent by winemakers in search of the perfect barrel for their wine. To make matters worse, this perfect barrel may be different for each varietal! There are three main species of white oak ( genus quercus ) used for barrels, and perhaps 20 or so regions in the world which are used as sources of oak. Then to add more complexity to the issue there are many dozens of companies producing barrels. Each cooperage has its own specific protocol for turning hunks of trees into barrels, and results very widely, much in the same way as different winemakers approach their task in different ways. Some of the many variables are: length of time of air-drying barrel staves (usually 12 - 36 months ), method of heating the staves so that they can be bent ( steam or fire ), and method of toasting the inside of the barrel ( head on or off, length of time, temperature of the flame ).
Most barrels these days are made to hold 225 liters ( 60 gal ). This size is reasonably easy to move around when empty, and provides a good surface-area-to-volume ratio. A barrel of this size is capable of releasing flavors and tannins into a wine for about four or five years; after that it functions merely as a container. Most winemakers prefer to have a collection of barrels of different ages, rather than all old or all new.
Winemakers, once they have bitten the bullet and committed to a certain barrel, have lots of options when it comes to putting wine in it. Some prefer to put the wine in barrels while it still contains a lot of suspended solids ( mostly yeast ), while others prefer to settle the wine to a higher degree of clarity first. Then there is the crucial decision of how long to leave the wine in barrel. Deciding when a wine has picked up the appropriate amount of oak is both difficult and highly subjective.
Although oak barrels are essential to the production of most fine red wine styles, their high cost - $550-$600 apiece for French barrels - means that winemakers are looking for alternatives. There are many pseudo-barrel-aging products on the market, ranging from finely ground oak granules to large chips to whole staves that can be inserted in an old neutral barrel or a stainless steel tank. These usually give some, but not all, of the characters associated with genuine barrel-aging.
Generally speaking, winemakers make a small addition of SO2 to wine after MLF has finished. However, some are now experimenting with leaving the wine without any SO2 until the following spring. In addition to having a slight antimicrobial effect in red wines, SO2 can affect the aging of the wine by acting as a donor of acetaldehyde, which aids in the polymerization and stabilization of anthocyanins.
The process of removing a wine from any solid material that has settled to the bottom is called racking. Racking a red wine during its time in barrel both serves to clarify a wine and also oxygenate it. Oxygenation helps to reduce the amount of H2S in the wine, and also to aid in the polymerization of phenolics. Robust, tannic red wines, especially, benefit from periodic aerobic racking.
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