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New
to wine: all about oak Let’s talk biology. When we discuss wine, we focus almost
exclusively on the grape vine, Vitis vinifera, in its many
varieties. But there are two other organisms crucial to wine
production that are often forgotten about. The first is the yeast, Saccharomyces,
without which our favourite tipple would just be grape juice. The
second – and the subject of this piece – is the oak tree, Quercus.
An odd choice, you might think. However, oak’s accidental
association with wine has been a critical one. The majority of fine
red wines are dependent on oak barrels for a vital component of their
flavour, as are a good number of whites.
The barrel-manufacturing process involves heating the staves
over a brazier so that they can be bent into shape. Somewhat
fortuitously, this slight charring – referred to as ‘toasting’
– coupled with the chemical properties of the wood, means that the
interaction of the wine with the inside of a new barrel imparts
pronounced flavour characteristics to the wine. When used
appropriately, new barrels can have a significant beneficial impact on
the wine that is aged in them. Another equally important, but less talked-about, effect of
ageing wine in barrels is that this allows a very slight and
controlled exposure to oxygen. Normally, winemakers do all they can to
avoid exposing their wines to air, but in this case the low-level
oxidation that barrels permit is beneficial to the structure and
character of the wine. So how does oak affect the flavour of the finished wine? For
red wines, barrels often add a little spice, enhance the structure,
and may add some sweet vanillin characters. A white wine that has been
fermented and aged in barrels will often have a noticeable nutty,
buttery character along with the spice and vanilla characteristics
that reds often pick up. Barrel aged wines are generally a little more
complex and have a more interesting texture than those aged in tank,
although some white grape varieties, such as Riesling and Sauvignon
Blanc rarely benefit from being oaked. A key difference in the effect of oak barrels is whether they
are made of French or American oak. If you ever get a chance to try
side-by-side cask samples of the same wine aged in French and American
oak, take it: the differences are marked. The relatively wide-grained
American oak imparts a much stronger flavour, with more obvious sweet
vanilla flavours and spicy notes. French oak has a more subtle,
slightly more savoury effect. Producers have to decide which suits
their wine better, although cost can be a factor here: French barrels
are much more expensive than American ones. The degree of ‘toast’
and even the manufacturer of the barrel are also important factors in
the effect barrels have on the wine.
Because new barrels are expensive, their use is usually
reserved for premium wines. But winemakers are only human: they want
the beneficial effects of oak for their cheaper wines as well, without
the high cost. As a result, barrel substitutes have become
increasingly popular. These can range from small oak chips in
teabag-like nets to barrel staves bolted into the inside of the tank.
Results can be variable, and are generally not as good as those
achieved by barrels. If you see the words ‘oaked’ on the label of
an inexpensive wine without mention of barrels, the chances are one of
these alternative techniques has been used. A hi-tech twist on this theme is a technique called
micro-oxygenation. This process aims to simulate the gradual,
low-level exposure to oxygen that occurs in barrel. A specialized
device is set up inside the tank that releases a slow stream of tiny
oxygen bubbles in a controlled manner. The exact scientific basis
isn’t clear, but it’s a technique that’s becoming widely
adopted. Converts claim that it enhances the structure, stabilizes the
colour, and removes unwanted vegetal notes from red wines treated in
this fashion. Increasingly, micro-oxygenation is being used in tandem
with oak chips in a sophisticated emulation of the process of barrel
ageing, but at a much-reduced cost. However, this is a technique still
in its infancy, and it’s hard to gauge its likely take-up with
winemakers currently using the real thing. Whatever happens, it looks
likely that the historical association between wine and oak is likely
to be an enduring one. 23/09/02 |
A
crucial variable here is the age of the barrel. New barrels impart the
most flavour, and this effect is subsequently diminished with each
re-use of the barrel, such that third-use barrels don’t add much
flavour at all. Many producers juggle their barrels carefully, ageing
their wine in a mix of new and used barrels to avoid over-oaking it.
Great care must be taken with the use of older barrels, since they can
harbour bacteria and yeasts that might contaminate the wine.