Strangely enough, when the wine world talks about barrels, they use the term ‘oak’. They don’t tell you the wine sits in barrels for a period of time, they tell you it has spent a period of time ‘on oak’.
What does oak do?
Oak has been used to store and transport wine for centuries. It’s resilient and non-porous, but just as importantly, it imparts flavour, tannins, colour, structure and complexity to wine.
New oak barrels allow miniscule, but continuous, oxygen penetration into the wine. This is an important factor in colour stabilisation in red wines. Young red wines often show an unstable violet colour, and the oak helps this to redden and stabilise.
Oak also assists excessive astringency in wines through polymerisation. What this means in simple terms is that the oak assists the phenolic molecules join together, forming larger and heavier chunks which then precipitate from the wine. This process actually continues in the bottle. No doubt you’ve seen the odd old bottle of red with all that sediment stuck to the sides. Now you know how it got there.
Oak is resitant to decay, fungus and insect attack, and has less shrinkage capacity than other woods.
Most wines these days are stored in stainless steel tanks, This is particularly true of the mass-produced, fruit-driven style of wines produced in many new world wine production regions. The same can be said of fermentation, unfortunately, as very often commercial winemakers suspend bags of oak chips in the wine rather than use barrels.
However traditional fortified wines [port, sherry etc] are still stored in oak barrels.
The most common sized oak barrels are the Hogshead [300 litres] and the Barrique [225 litres]. Sherry producers use large barrels that hold 600 litres – although they only use 560 litres of that room [see Spanish wine regions pages for more info], and some Chianti barrels hold much more [as with the large ones pictured on this page].
The size of the barrel comes down to the desired level of oak influence in the wine. Fresh Chianti doesn’t need a lot of oak treatment – it is meant to be drunk young, with fruity characters.
Where does the oak come from?
Whilst oak trees of various species grow around the world, it is the French and American oaks that are of primary interest to the winemaker.
Russian oak has also appeared in wineries around the world – quite possibly due to the expansion of the industry in the past couple of decades, and is making a bit of a name for itself.
Small quantities are also used from other European countries, England and Canada.
Now let’s get technical. Oaks come in red or white species. Red oak is too porous, so only white oaks are used. There are three main species of white oak used for winemaking, two from Europe [Quercus sessilis, and Quercus penduncalata], and one from North America [Quercus alba].
If you want to go looking, you’ll find American oak mostly coming from forests east of the Mississippi River, whilst in France, the popular oak forests are found in Limousin, Nevers, Allier, Troncais, Burgundy and Vosges.