Barrel maturation
Next to the wine grape itself, the wooden barrel is the most important determinant of the style, flavour and quality of the wine in your glass - a wooded wine, that is. It's not an exact science, yet much of it is about chemistry. The balance lies in the philosophy of the winemaker. Trying to see the wood for the trees is Wendy Toerien.When learning to 'taste' wine - really 'taste' it, with all levels of sensory perception and powers of association - one ends up drawing on an overwhelming amount of information as a reference. That sweetness: is it ripe fruit, vanillins from American oak or an extra few grams of unfermented residual sugar? The spiciness: French oak? Varietal Shiraz? Cool-climate terroir? Oh, yes, that's pure coffee, no, mocha on that wine! So is it a Merlot or does that indicate excessive wooding? Or even heavily toasted new barrels?
Wine is made from different grapes, each with distinctive characteristics. Then there are different clones of the same grape, with varying aromas and flavours. Plant the same variety on different sites, with different soils and micro-climates, and one ends up with two different wines. Inoculate with different yeasts (or use natural yeasts) and the aromas and flavours extracted will be affected. Take the same wine, ferment some in tank, some in barrel, and again: the results will vary. Use barrels from different coopers, and the wine will be as different as night is from day. Confusing, no?
While the full range and exact process of the chemical effects of wood on wine have yet to be explained, it is known that there are a variety of wood substances imparting flavours and personality characteristics without actually changing the wine. Some are directly absorbed, some react, others merely affect our sensory perception of what we're smelling or tasting.
Ever smelled coconut on a wine? Lactones create that character. A more heavily toasted barrel can increase that apparent oakiness, while open-air seasoning of the staves used to make barrels, lessens the effect of lactones.
How about vanilla? That's quite a common one. Phenolic aldehydes in the wood are responsible. These are brought out during the seasoning of the wood staves, as well as the toasting process. Yet, when a wine is fermented in barrel, these phenolic aldehydes are far less noticeable.
Spice such as cloves or the piquant scent of a carnation bloom is attributable to volatile phenols. Again, this character is lessened with the duration and type of seasoning the wood staves undergo.
Among a large, complex group of compounds called carbohydrate degradation products in wood, are furfurals, released when wood sugars are toasted during barrelmaking. Flavour association? Bitter almonds. But yeasts can change this bitter characteristic into new compounds with flavours of smoked meat and leather. Other carbohydrate degradation products extracted during barrel toasting are maltol and cyclotene, which give a wine caramel-like aromas.
One of the more important wood extracts is tannin (other tannins in wine come from the grapeskins and pips during crushing). Besides deepening colour and giving wine a lively astringency, wood tannins actually help protect it from oxidation when exposed to air during the winemaking process. On the other hand, when wine is made in a consciously reductive style (minimising contact with oxygen) - especially beneficial with white wines which are more sensitive to oxidation than reds - tannins are essential in combatting unpleasant aromas (hydrogen sulphide and mercaptans) which can also give a wine a 'dirty' taste and eggy off odours. This problem can be solved by aerating a wine, usually by racking or by micro-oxgenation: releasing small, controlled amounts of oxygen into a wine fermenting in tank.
Finally, the baddies…bacteria. With wine being alive and biologically active during fermentation and maturation, bacteria are inevitably present. But when working with wood extract, bacteria can transform these compounds into attractive aromatics: smokiness, cloves and coffee.
Bring yeast into the equation and the results become even more interesting. Barrel fermentation also produces more polysaccharides (complex sugars) that add richness and apparent length of flavour on the palate. The release of polysaccharides can be further increased by yeast mass and the frequency with which the lees is stirred.
Spare a thought for the winemaker selecting his barrels each year… at around R6 000 a shot; which produces about 290 bottles of wine. Here are additional factors they have to take into account:
Was the oak from which the staves were made, hand-split or machine-cut?
Some expert palates maintain they can taste the difference between resultant wines. Sawing wood exposes more grains which release more raw tannins. Twice as many staves are produced from a piece of oak cut by machine than by hand-splitting. And because American oak is less porous than French, staves can be cut across the grain. Which makes machine-cut American wood economically attractive - and the oak influence on a wine so evident. Most French oak is hand-split and, even when machine-cut, always with the grain, so the oak effect is more subtle.
Was the wood kiln-dried or seasoned in the open air?
The French prefer air-drying for between 18 and 36 months. A kiln takes 12 months: it's more cost-effective and there's less threat from pollutants. Yet some coopers maintain that the drying time is not as important as the wood's exposure to the elements: rain and temperature. Natural drying does appear to reduce and modify the structure of the stable extractable compounds of wood, increase aromatics and deliver less tannic wines. Studies have shown, however, that it's not the actual tannin levels, but the sensory perception thereof that's influenced.
Once the staves are heated, bent and the barrel hooped together, the toasting (using a brazier filled with burning wood chips) becomes paramount. Heating and toasting the staves and barrel modify the chemical composition of the wood, the results of which were discussed above. Another function of toasting is as a buffer between wood and wine: the heavier the toast, the more subtle the interplay. But a high degree of toast can leave its mark more overtly in the form of a distinctly charriness.
So, what's a winemaker to do?
Here's what three vintners have to say: Jordan's Gary Jordan, De Grendel's Charles Hopkins (formerly with Graham Beck Franschhoek) and Cordoba's Chris Keet, all members of the Cape Winemakers Guild committed to excellence in winemaking through ongoing exploration of the art - and science - of their craft.
On wooding in general? Charles Hopkins: "I'm not a great fan of new oak on reds. It may sound harsh, but the only way I can describe the tendency of some to subject a wine to 100% new wood is as 'rape' by oak. I like to capture the primary varietal fruit flavours of the grape. People think I'm crazy, but I've made a 2004 Shiraz from grapes bought from [cool-climate] Elim: lovely fruit, with all that beautiful varietal spiciness and white pepper character. I decided to mature in fourth-fill oak only - by the fourth year I reckon there are minimal oak flavours imparted to wine; the barrel is mainly a vessel and then it's just about oxygenation and the softening of the wine."
On wood's effect on different varieties
Chris Keet: "Merlot, for example, though tough in the vineyard, overreacts to wood. But Cabernet Franc just gobbles up new wood! I've put the Cab Franc from my oldest block [about 22 years] in 100% new wood and the five new blocks planted since 2000 in about 50%-60% new wood. But I 'manipulate' my vineyards to the extreme which results in exceptional fruit with that typical varietal character of herbaceousness and dusty tannins. So, to match that, I'm looking for something I can only describe as pencil shavings, slightly spicy, a fragrant cedarwood character… Actually, it's easier to tell you what I'm not looking for: sweet vanilla from American oak; furfurals like coffee and mocha; toastiness… So my barrel choice is French oak from Taransaud and Sylvain which share an understated house style: a good tight grain and medium toast, ever so slightly charred over a long, slow fire. Charles Hopkins: "The wood flavours should complement the varietal character of the wine. The coconut sweetness of American oak works well with Shiraz and Pinotage. But French oak is best for the Bordeaux varieties."
On coopers
Gary Jordan: "Seeing as we specialise in our soils [varieties are carefully matched to sites] it makes sense to specialise in the cellar. Besides reserving different areas in the winery for the different varieties - to control handling, temperature and so on - we are very specific about our barrel shapes and wood types. Burgundian for Chardonnay, Bordeaux for reds. We select our coopers for their specialised knowledge of what a particular variety requires from a barrel. Each has a house style, and after years of trying out the various ones, we know what we want and we've settled on those who provide consistency of style. We use five different coopers for our Chardonnay alone!"
On barrel fermentation
Gary Jordan: "Barrel fermentation is preferable because, by putting fresh juice into wood, without alcohol and SO², both of which extract a lot of oakiness, one gets a softer result. Juice and wood marry better than wine and wood. People don't want to be carpenters to get through a bottle of wine!"
On wood grain and levels of toast
Gary Jordan: "The Burgundians produce a tighter grain [for slow release of wood extract], the Bordelaise a medium to open grain. One of our favourites, Francois Frères, make a tight grain, medium-toast, which works well with the limey, citrussy character typical of our Chardonnay. Rousseau is similar - both have a slightly charrier toast, more Meursault-like. By comparison, Dargaud & Jaegle and Taransaud [a Bordeaux cooper which has opened up a cooperage in Beaune to produce Burgundian barrels] supply a deeper toast, less charry, to complement our other Chardonnay which shows more tropical fruit character. Wood choice must complement primary fruit flavours. We don't want to emphasise an already strong lemony, citrussy character, but rather add to it, ultimately increasing the wine's complexity."
On barrel costs
Charles Hopkins: "New oak barrels can add about R18 to a bottle of wine - that's the highest cost component after the grapes. Using a combination of fills, you can bring that down to about R11 a bottle. That's not counting issues like space taken up and risks involved with spoilage."
So why do battle with the barrel? Chris Keet: "Quite simply, putting wine in a barrel is the most natural way to 'add' flavour and complexity."
