Oak influences different wines in many different ways and the
winemaker’s job of selecting the correct barrel and then judging the
correct application is an art in itself. Oak is the only permitted flavour
altering additive, and one which forms an integral cog in the
evolutionary mechanics of wine. As such, it deserves close attention.
There are three major barrel producing areas across the globe:
France, the USA and Eastern Europe, and the origins of a barrel often
hold important clues to its attributes.
French Oak (Quercus petraea/robur)
The craft of barrel-making was born in France, where the Gauls produced wooden storage vessels for wine known as ‘cupals’. The craftsmen who made them were ‘cuparius’,
from which we get the modern word ‘cooper’ (although the earliest
recorded use of wooden storage vessels far pre-dates Christian times).
French oak has a wide array of flavours
that can be extracted – including spicier notes and there is also
noticeably higher tannin content in French oak. Oak is sourced from
state-owned forests at premium prices, and must be hand split with the
grain, making for some of the most expensive barrels available, prized
for their quality, imbued by the workmanship and nous of a trade that
takes 7 years to master!
American Oak (Quercus alba)
American oak is structurally different from European oak and tends to be higher in wood sugars as well as flavour compounds responsible for vanilla and caramelised
notes. The woods tend to be privately owned and lower priced, and the
straight grain means it can be machine cut (as opposed to hand split as
in France) – meaning a yield four times that of European oak.
Hungarian/Slovenian Oak (Quercus petraea)
Genetically similar to French oak, however slower growth means a
tighter grain and less extraction, as well as lower tannins. The oak
also reacts differently to the toasting process, producing a unique set
of flavours. It is priced mid-way between French and American oak and is often used to add complexity.
Toasting a barrel is the process of burning a wood fire in the centre of the oak staves, charring them. This process creates and releases certain desirable flavour
compounds in the wood which are in turn extracted by the wine during
barrel maturation. Toast is measured from light to heavy and each level
results in different flavours. Oak sourced from different areas and climates respond differently to the toasting
process; to judge which level of toast will most benefit the character
of an individual barrel the cooper uses experience, skill and intuition.
Size plays a significant role in the way wine extracts flavour – the larger the barrel the higher the ratio of wine to extractable flavour compounds and thus the more subtle the perception of oak. The most common size is the 225-litre Bordeaux barrique, although the 300-litre hogshead has also become popular of late. 500-litre barrels are also common. Large wooden vats with a capacity of more than 1 000 litres are known as ‘foudres’ and can be used for many years.
When a barrel is filled with wine for the first time it is called a
‘first fill’, the second time it becomes ‘second fill’ and so on. The
significance of this lies in the limited supply of extract available.
The first fill of a barrel absorbs about 50% of the flavour
and tannin in the barrel, the second fill 25% and then less each year
as the barrel ages until it is merely a storage vessel, imparting little
flavour. Often the winemaker will use a mix of barrels,
perhaps 30% first fill as with the Creation Syrah, with the balance
being made up of wines in second and third fill barrels. The wines from
the different barrels will be pumped into large tanks and blended before
bottling.
Apart from imparting flavours,
oak barrels are also uniquely suited to the slow aeration and
maturation of young wines. The process of racking wine from one barrel
to another, leaving any sediment behind, also oxygenates the wine.
Oxygen is extremely important in the tannin development and integration
as it allows tannin molecules to polymerize and become less obtrusive,
improving the mouth-feel of the wine. Oxygen also interacts with certain
flavour
compounds to impart desirable aromas. The rate at which wine evaporates
from barrels requires it to be topped up every couple of weeks, or
there is a risk of too much oxygen which causes the wine to oxidise.
Barrel maturation is a vital process in the journey from grape to
glass, and one which requires patience. White wines benefit from less
time in oak than red wines, and on average spend 6 to 10 months in the
barrel. Delicate reds like Pinot Noir spend between 10 and 12 months in
the barrel – the relatively low tannins in Pinot Noir do not benefit
from extended time in oak, however the ratio of new oak is key to the
wine’s style. Heavy reds can handle much longer periods in oak,
mellowing and developing complex aromas and flavours. At Creation they spend 14 to 18 months in the cool, slightly humid stillness of the barrel maturation cellar.
The neat collection of French oak barriques, stacked four high, is
visible through glass inserts in the floor as you enter the Tasting Room
at Creation. During their stay the wines will switch barrels three times, each time becoming clearer and approaching readiness to drink as they leave sediment behind in a process known as racking. Racking is the gentlest way to remove suspended proteins that make wine cloudy. Using fining agents to clarify wine can often result in some positive characteristics being lost as well.