The oldest illustration of a barrel is an ancient drawing in the tomb of Hesi-Re (also known as the “Chief of Dentists and Physicians”) who lived during the Third dynasty of Egypt. The illustration shows wooden barrels held together with wooden hoops. Those barrels were not used to transfer wine but as a corn measure. Wooden barrels were later on used to transfer several goods such as milk, beer, water and wine. Barrels seemed to be superior to the relatively fragile clay vessels; their shape made them strong and easy to transfer. This was the primary reason why wooden barrels became so popular during that period.
But there was something else discovered later on that made wooden barrels a necessity for winemakers. The old-timers realised that storing wine in wooden barrels made it smoother and improved its taste and aroma. This is the only reason we still use wooden barrels today.
As most of you may already know white oak is the main wood used to produce wine barrels. Oak trees grow large, straight, and tall which helps to minimize wood loss during production. Oak is also straight-grained which means it has vessels and fibers running parallel to the length of the trunk.
White oak can hold liquids better than other types of wood. Its pores are plugged with tyloses (Image 1), which help make white oak suitable for water-tight vessels. In addition white oak rays are unusually large and exist in high proportions (28% of the wood) creating a major barrier to wine and air transfer.
The high proportion of rays gives oak much of its flexibility and resilience. Otherwise, the staves would be too tough to bend so as to form the curved sides of the barrel without cracking.
Besides being a superior wood, white oak is also favored for its unique aromatic characteristics.
There are three basic species of oak used today for wine barrels: the Quercus alba which is found in north America, Q. robur, and Q. sessilis which are found in Europe. Each species has its own individual characteristics and can influence a wine differently.
There are some general differences between the American oak and the European oak. The American oak tents to grow faster which results to wood that is denser, harder to work with, has lower extractives and allows less oxygen to enter the barrel. On the other hand the European oak grows slower which means it its softer, easier to work with, has more extractives and allows more oxygen to enter the barrel.
Just like vineyards, oak trees are influenced by the climate and soil they grow on, which means in some areas of Europe the oak trees will give you more tannins and in some other areas they will give you less tannins. None of the above choices are wrong, both American oak and European oak are equally good. It is up to the winemaker to decide what kind of oak he needs for his wine.
The winemaker can also choose the level of toasting. Toasting is a very important part of the barrel production process. Essentially the inner part of the wine barrel is heated with an open flame either by burning small pieces of oak or using gas fire. The process helps the barrel-maker to bend the wood to the desired shape. More importantly, toasting is responsible for the pleasant aromas we encounter in wine. We have three main toasting categories, light, medium and heavy.
With light toasting we release aromas such as fresh oak, subtle aromas of vanilla and coconut. In general light toasting does not give you much more aromas than the wood would already give you. This kind of toasting is used for wines that we do not want to enhance their aroma. (This will make more sense later on when we explain the rest of the barrel aging benefits).
As the barrels are heated up for a longer time, the sugars of the oak start to caramelize. This forms complex and toasty aromas such as vanilla, coffee and fresh baked bread. Wines aged in such barrels become round and develop flavors such as butterscotch, vanilla and caramel.
At this stage the barrels start to lose their vanilla and chocolate aromas and develop more smoky and spicy aromas such as roasted coffee and black pepper.
Tannins are very important for red wines and are mostly found in grape skins. Oak also contains small amounts of tannins that are released into our wine during aging. These tannins contribute to the improvement of mouth feel (body) and astringency in our wine.
Something else that most people would not associate tannins with is color. Tannins contribute in the color stability of our red wines (polymerisation of anthocyanins with tannins). However color stabilization cannot happen without the presence of oxygen. This leads us to our next barrel benefit, micro-oxygenation.
As we mentioned before oak barrels are very good in holding liquids and isolating wine from air, but this is not entirely true. Barrels actually allow small amounts of oxygen into our wine (micro-oxygenation). There are several chemical changes happening to our wines during barrel aging and these changes make our wines taste better. Other containers such as stainless steal tanks are cheaper and last for a lifetime but the downside is that they are entirely airtight. Such containers are perfect for storing wines that we do not want to develop more. This subtle introduction of oxygen helps our wine become smoother by mellowing the harsh tannins (polymerisation of tannins) and giving more body to our wines. This is the reason why winemakers use also lightly toasted barrels or very old barrels to age their wines .
With today’s technology there are micro-oxygenation machines that mimic this process and can introduce the exact amount of oxygen you want. There are also oak barrel alternatives such as oak chips and staves that are cheaper and release extracts much faster. In other words a winemaker could essentially replace barrels if he wanted. Barrels though have been part of our winemaking culture for centuries. From an aesthetic point of view wine barrels are very important. Wine barrels are the main attraction in wineries and for most wine enthusiasts a winery without wine barrels is not a winery. For a lot of winemakers barrels are not just another tool, barrels are an expression of their approach towards winemaking.