During a recent training session with some restaurant staff, I was asked why a wine might have ‘reserve’ or ‘riserva’ on the bottle label. This led on to a discussion about ageing wine in oak and the effects this has. The thought of barrels stacked in a cellar, quietly sleeping, is a romantic one. But why is wine often aged in oak barrels? Ageing wine for a period of time in oak barrels is seen as a sign of quality for various reasons, the main 2 being:

• Exposure to oxygen at a slow and controlled rate, which will allow the wine to develop new flavours
• The addition of new flavours through the type of wood used and how old the barrels are

When a wine is aged in oak, it will usually be designated on the front of the bottle by words such as ‘riserva’ or ‘reserve’. These words will tie to a legal ageing requirement in Europe, but outside of Europe the legal meaning of these words is less structured. The type of oak will make a difference to the flavour profile as well and will add flavours such as:

• Oak
• Smoke
• Vanilla
• Coconut
• Cinnamon
• Nutmeg
• Coffee

These flavours come from a range of factors:

• The type of wood, usually one of the following:
  • American oak – This is cheaper because it is denser and can be sawn, rather than having to be split by hand and is therefore less labour intensive. It will give stronger flavours, which will usually be predominantly vanilla and coconut
  • French oak – This will give a more subtle flavour profile and will be more sweet spice, such as cinnamon and nutmeg
• The usage of the barrel. If a barrel is new it will impart a lot of flavour into the wine over a shorter period of time. The more times a barrel is used, the less flavour it will have left in it. Once a barrel has been used 5 or 6 times, very little flavour will be imparted into any wine aged in it.
• The level of toast that the barrel received. An oak barrel will be toasted on the inside when it is produced. This will determine the strength and intensity of the oak and smoke flavour that can be imparted to the wine.
• The size of the barrel. The larger a barrel is, the less wine will be in direct contact with the oak. This will make the new flavours more subtle and less obvious if the wine is aged in a very large vessel.

Another reason wine is considered to be of a higher quality when aged in oak, and probably the more important reason, is that the ageing in oak will allow oxygen to come in to contact with the wine through the wood. This is because oak is a porous material and oxygen can pass through it, although at a very slow rate. This slow and controlled contact with oxygen will age the wine and allow new flavours to develop over time, such as:

• Leather
• Stewed fruit (plums and raspberries etc)
• Dried fruit (prunes and raisin)
• Jam
• Earthy
• Eucalyptus

These complex flavours that develop can take a long time and will be the result of the wine’s molecular structure changing and can only be achieved through patience and skill of the wine maker. The longer the wine is aged will also allow for flavour to marry together and for the wine to become more integrated or, a word that is used more commonly in the wine world, structured.

The best way to think about this is a glass of wine you pour and leave on the side for a few hours. Over this time the wine will change in flavour and eventually spoil. This is the effect of oxygen ageing the wine. These wines aged in oak are changing at a much slower pace and when they reach the point the wine maker wishes, they will be bottled and sometimes aged further inside the bottle before they are released.