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One of the things I love about wine is its link with tradition. While technology such as refrigeration and stainless steel tanks have made inroads into modern wineries, the basic winemaking approach is pretty much the same now as it used to be 50 or 500 years ago, if that's how you want it to be. I really like that. If you had the desire, you could build a winery using medieval techniques, and make brilliant wine in it.

One of the links with tradition that even the most modern of wineries maintain is the use of oak barrels. A couple of millennia ago large clay amphorae were the storage medium of choice for liquids such as wine. But these are heavy and breakable, and so when oak barrels came on the scene, they proved extremely popular.

And, by happy coincidence, wood suited wine very well. Oak, the wood most commonly used for barrels, is not totally inert. It has an interaction with wine that skilled winemakers have used to their advantage.

The first thing is that oak barrels leach some flavours from the wood into the wine. The second is that they donít exclude air completely, but allow the wine to be exposed to a constant but very low level of oxygen. Both of these can be a good thing; they can be bad. It depends. It is for this reason that the nature and quality of oak matters a good deal in barrel construction.

The two main types of oak used for wine are French and American. French oak is finer grained and more expensive; American oak is cheaper and gives the wine more flavour, but this flavour tends to work better with richer, more robust wines. The flavour compounds from oak include those that give a vanilla/coconut character, of which there are more in American oak, and also those which give toasty, spicy, woody notes. Sometimes wood can give slightly bitter green notes, and these aren't desirable. I also get a bit of tar-like character from some oaked wines.

For use in barrel construction, oak is cut into small pieces called staves, which are then used to make the barrel. These are seasoned for a period: three years outdoors is the ideal, in a climate where there is some rain. If the seasoning is suboptimal, undesirable flavours can remain in the oak ready to be transmitted to the wine.

During barrel construction these staves are joined together with metal hoops, and then heated over a fire to soften the wood and make it pliable. This heating process can char the inside of the barrel, and the degree of charring or toasting is important in how the barrel will interact with the wine. Itís another variable.

New barrels impart more flavor to wine than old. Barrels are re-used for several years, and the amount of new or old oak used in a wine is important. The use of too much new oak, which makes the wine taste oaky, is widely considered to be a wine fault. And some wines are better able to cope with oak than others.

Most serious red wines are aged in barrel. But barrels are expensive, and so alternatives have been tried. One is to bolt oak staves into a stainless steel tank. Another is to use oak chips, toasted according to the winemakers desire and then added to a barrel of wine. These oak alternatives don'rt give as good results as using barrels, but this may partly be because the oak used is of lesser quality and isn't seasoned as well. What this means is that even modern wineries will usually have some barrels Ė perhaps their only link with the past.  

Oak staves that have been in a tank of red wine

You'll gather from all this that oak is a complicated subject. For a winemaker, barrels are a critical tool, and choosing the right ones and using them in the right ways is one of the main ways that winemakers can alter the flavour of wine.  

See also: how barrels are made

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