During my visits to the cool dark cavernous wine cellars of the Douro and Dao I often find myself wandering between rows of wooden barrels. Most of these barrels are around the 500 litre size we are accustomed to but now and again there are some truly gigantic barrels !
Why the different sizes and why wood ? It wasn’t always this way. In the dim and distant past (around 6000 BC) in places like Armenia and Georgia wine was stored in clay amphorae buried in soil and these vessels stuck around for a long time. With their rapidly expanding empire the Romans discovered that one of the benefits of changing from clay amphorae to wooden barrels (apart from being lighter and more easily handled) was that the wine reached the end of its journey tasting better than when it started !
So what happened on the journey ? Well it seems that unlike clay, wood is porous and allows air through and some oxidation to take place. This slow exchange of oxygen smooths out the tannins and some vanilla and toast flavours seep out from the wood. The wood was mostly oak due to the abundance of oak forests in Europe, the flexibility and tight grain of the oak also made for a watertight vessel.
The main varieties of oak are American or French. In France the cool climate, slow growing and tighter grain gives a more subtle and spicy result while American oak is more porous with sweeter and more vanilla flavours. Only young oak imparts flavour and sometimes wines are stored in older barrels so that they will not take on any flavours of the barrel.
Back to the sizes – it seems to be to do with surface area and contact with the wine inside. The smaller the barrel the more wine is in contact with the wood and the mellowing effects are greater. Put young port wine into a smaller barrel for a few years and the wines lose their intense berry flavours and deep red colours and take on mellow oxidative aromas of caramel and nut and a pale amber hue known as tawny.
Alzira Carvalho, wine maker at Quinta Santa Eufemia explains;
‘In Douro the usual measure of the barrels is 550 litres, but they have different sizes. We have many pipas with 605 litres, but you can find some want 700 litres, 750 litres and others want 500 litres. The smaller they are the better for the oxidation of the wine and for Port wine that is the main objective of the wood. If you Ahave a glass front on the barrel, you will see many bubbles of oxygen near the wood. Those oxygen is fundamental to the oxidation of the wines that is responsible for the development of the complex aromas and the colour.
For the ruby ports you don’t want that kind of aroma and you want a red colour. That is why for rubies we use big barrels where there is not so much oxidation”.
This also seems to apply to the fortified Moscatels made on the high plateau above the Douro valley. Rui Cunha of Secret Spot wines…
“For the 10 Year and 40 Year Moscatel we use barrels from 225 litres up to 3,000 litres. For these two wines we search used oak, regardless of the origin. The older the better. It should not give oak flavours or tannins just oxygenate the wine. Most of our barrels are made from chestnut or from a mixture of different oaks. The 3,000 litre barrel we have is so large it was built in the adega”.
So next time you are swirling the golden tawny port around your glass and inhaling those lovely aromas just think how much of that has come from the barrel itself !