When I write about a wine’s flavor profile, I usually include whatever a winemaker’s tech sheet states about barrel aging, how many months in barrel, how old those barrels might be, and often the country of origin. I include this information because it very generally suggests to what extent those barrels have contributed to the flavor and texture of the wine. The newer the barrel the more it imparts flavor and texture. So to some extent, the information is a clue in part of what we’ll taste when we pour the wine into a glass. But what flavors and what texture are we talking about?
After researching the subject, I’m in awe of the complication that a winemaker considers when he or she decides which barrels to use for a particular wine because the contribution the barrel makes to the wine is enormous. And this is exactly the reason that some winemakers of both red and white wines avoid barrels altogether and ferment and age their wines in stainless steel tanks when they want to present only the authentic flavors of the grape.
In an older time, winemakers would have given no thought to barrels because barrels would have been made from whatever tree type grew locally, and anyway barrels would have been little more than storage containers for the wine among other commodities like olive oil or even earlier salt. Not so today. Winemakers choose barrels made from particular wood from particular forests in different parts of the world, the wood seasoned or aged for a particular amount of time before being made into barrels of differing sizes, and those barrels toasted to varying degrees. The final consideration would be how many years the barrels had contained wine from new to one, two, three, or many more years.
Many techniques now exist for softening the tannins in red wine, that gritty sensation that in the extreme can be entirely unpleasant. But its absence would be a smoothness that is typical of fruit juice, which would not have the palate cleansing effect, together with acid, that makes wine so compatible with food. Barrels tame tannins because wood is porous and admits a very controlled amount of air, which in turn oxides the wine over time and softens it. When we decant a younger tannic red, we do so because pouring the wine from the bottle into a decanter exposes it to oxygen and hopefully provides a quick oxidation that smoothes the wine. Allowing wine to sit in the glass does the same thing. And of course in an opened bottle of wine, noticeable oxidation will occur until the wine eventually tastes like vinegar.
Once the world decided that oak was the best wood for aging wine, forests in the U.S., France, Croatia, and Hungary among other countries provided the most wood for wine barrels, French oak being the least porous and most prestigious because it allows longer and slower aging. So if a particular grape, Cabernet Sauvignon for example, is more tannic than another one, Pinot Noir for instance, it will require more time in barrel.
Wine undergoes clarification and stabilization in barrel. As solids drop out of solution and collect at the bottom, the clearer wine is racked into other barrels, leaving behind the sediment. Racking from one barrel to another also oxides the wine a bit more and further softens the tannins. Additionally, the time spent in barrel intensifies wine color, especially red wine.
Wine is alive while in barrel, the yeast and other substances extracting flavors from the wood itself. And different wood from different forests in different places produces different flavors or different proportions of flavor. Certain aromas like coconut can increase with barrel time. The amount of toasting that the barrel has undergone amps up this flavor, and the flavor of vanillin increases with the amount of toast. Other components of the wood can contribute spice and caramel. Yet other elements in the wood contribute smoked meat and leather or in white wine clove and coffee. We’ve heard these descriptors countless times. But once we recognize that they are barrel flavors, not grape flavors, we understand that winemakers need to control all of these influences so as not to obscure the flavors of the fruit itself and leave it vulnerable to the ruinous descriptor, too oaky.
When we consider all of these contributions that oak makes, it becomes clearer that winemakers need to match the flavors of the barrel with particular grape varieties. They need to regulate how much of these flavors ends up in the wine by choosing a particular barrel size. Generally, Europeans are less partial to oak flavors than Americans and age their wines in larger casks so that that the larger volume of wine has less contact with the surface of the wood. Or they might mitigate oak influence by using not just larger barrels but also older barrels whereas new world winemakers are likely to use newer barrels or at least subject a larger portion of a particular batch of wine to newer barrels and less to one, two, three or older barrels where flavor components have already been extracted by previous wines. Newer wood barrels also have tannin. So a ripe and higher alcohol California wine for example, made from very ripe fruit may lack tannin. So aging it in new oak barrels would benefit the wine and give it texture that it wouldn’t otherwise have. Winemakers also need to determine how long to leave wine especially in newer barrels.
I don’t know about you, but my head is spinning at this point, and I’m glad that I don’t have to make any of these decisions. But I do have to choose wine for your table and mine, and hopefully knowing something about barrel aging will help both of us understand what we can expect in the glass. But in your case, you’re not likely to see a tech sheet when you reach for a wine on a shelf. Good luck to us, who love wine but maybe not all of it. Ultimately, buying a bottle is an act of trust. But like everything else, each bit of knowledge helps.
Grain, Seasoning, and Toast
Three decisions shape a barrel before any wine touches it. The grain of the wood determines how quickly its compounds move into the liquid, the seasoning period outdoors lets rain and microbes soften harsh tannins, and the toasting over fire converts wood compounds into the aromas the barrel will contribute. Change any one of the three and the same forest produces a noticeably different barrel.
Toast level is the most direct lever. Lighter toasting leaves more raw wood tannin and less sweet aroma, while heavier toasting builds the caramel, smoke, and spice notes described above at the cost of the wood’s own structure.
Barrel size matters as much as species. A larger cask holds more wine against proportionally less wood surface, so its influence is gentler and slower, which is why cellars aging wine for years often favor big casks over small barrels.
American Oak and French Oak
| Trait | American white oak | French oak |
|---|---|---|
| Grain | Generally wider | Generally tighter |
| Milling | Can be sawn | Usually split along the grain |
| Aroma emphasis | More overt coconut and vanilla | Subtler spice and toast |
| Flavor release | Faster | Slower and more gradual |
| Relative cost | Lower | Higher |
American white oak is the species Quercus alba, one of the several hundred oak species in the genus Quercus, while French barrels come from related European species grown in managed forests. Once those differences are clear, a technical sheet listing barrel origin and age stops being trivia and starts predicting the glass, a theme running through our wine skills and knowledge collection and the food and wine pairing guide.