Oak is the most important and most expensive input in many wines after the grapes themselves. We talk a lot about the origins of grapes and the techniques of winemaking, but how much do we know about the sources of barrels and how they’re made? As modern winemakers hone in on the detail of every stage of production, the intricacies of different oak forests, wood grain, seasoning, toasting, barrel size, age of barrels, time in oak, even how long it takes a new barrel to reach a winery – not to mention all the alternative oak products that winemakers don’t want to talk about – have never been more important.

Australian winemakers spend some $40M on oak every year, but they’re buying just half the number of barrels they were a decade ago. “Five or ten years ago the customer was after intensity of coconut and vanilla flavours, now they’re looking for subtlety and length,” says Treasury Wine Estates Group Winemaker Sam Glaetzer, who oversaw all oak purchases for the company until recently. And it’s not all about barrels. The myriad of alternatives available to winemakers to achieve oak characters in stainless steel tanks has never been stronger. The landscape of oak options is growing so quickly it’s starting to look more like a jungle than a forest out there.

Where does oak come from?

Oak for wine barrels is farmed all across Europe, eastern United States and even Japan. The US is the largest supplier, producing some two-fifths of the world’s barrels. France is the largest source of European oak, supplying one-quarter of all barrels, though eastern European oak is growing rapidly. Numbers are sketchy, but it’s rumoured that Russia’s oak forests outrank all others. French oak has become the standard by which all oaks are judged, though this hasn’t always been the case, with Baltic and Slavonian oak preferred in the 19^th century.

Three species of white oak are most important for wine barrels: American white oak and two European species, often grown together and not differentiated. Coopers are more interested in origin and grain size than oak species. <Omit this paragraph if space is short.>

French oak regions

France boasts more than four million hectares of oak forests, covering one-twelfth of the country. There is no Appellation Contrôlée for the origin of oak like there is for wine, and confusion abounds regarding the exact regions, so much so that a number of coopers have abandoned specifying forests at all, preferring to blend across forests for consistency. The main regions for French oak are:

Western Loire and Sarthe (south of Paris)                 Highly prized, tight-grained oak.

Limousin (west of Bordeaux)                                        Wide-grained oak, imparting more tannins. More popular for brandy than wine.

Nevers and Allier (central France)                               Close-planted forests producing tight-grained and popular oak.

Vosges (near Alsace)                                                      Tight-grained, similar to Nevers and Allier, with a whiter colour.

Jura and Bourgogne (east of Burgundy)                     Traditional oak for Burgundy.

Argonne (near Champagne)                                         Tight-grained, not dissimilar to Vosges.

Grain

Oak is classified as either tight or wide-grained. The slower the growth of the tree, the tighter the grain and the less porous the wood. Wider-grained oak tends to impart more tannins than the more highly prized tight-grained. European oak species are naturally more porous than American oak, and are more likely to leak from the end grain if not coopered carefully. This is why the end grain of the staves of European oak is sometimes painted.

American or French?

American oak is less expensive and generally has more powerful flavour, more obvious vanilla and coconut characters, and more astringent tannins than the more subtle European oak. It’s well suited to more powerful red wines and hence used widely across Spain, North and South America and Australia.

A trend toward more subtle oak in Australian wines has led a movement away from American toward French oak over the past decade. “It’s the big irony of paying over $1100 a barrel for something that’s not going to impart a whole lot of flavour!” says Dan Buckle, who led a switch to 100% French oak in shiraz during his tenure at Mt Langi Ghiran. “We’re looking for subtlety and elegance and a minimum of oak flavour, and you pay a lot for that.”

American oak had its origins in the Bourbon industry, and it was only in the early 1990s that its coopers started to get serious about wine barrels. Since then, the trajectory of refinement has been steep, not only in the origins of the oak but in grain selection, seasoning and coopering.

“We’ve always had access to good American oak, but the quality has improved dramatically in recent years,” reveals Penfolds Senior Red Winemaker, Steve Lienert, who’s been making red wines for the company for 35 years. “We have greater selection of the oak types, allowing us to avoid harsh characters, producing wines with more drinkability when they’re young, even though they will age.”

Seasoning

Treasury Wine Estates has traditionally purchased raw oak from America and brought it back to Australia for seasoning. A recent change to seasoning in America has dramatically improved quality.

Seasoning is the process of drying oak after it has been split or sawn. This can be achieved in a kiln over 12 months, but tends to produce more aggressive tannins. Air-drying between 18 and 36 months is preferred, to reduce aggressive tannins and heighten the aromatic potential of the wood. Australia’s hot, dry summers make local seasoning more akin to kiln drying, compared with the cooler and more humid conditions of France or the wet summers of Missouri or Kentucky in the US. Australian-seasoned oak is therefore higher in vanillin and lactones (coconut, spicy, earthy and herbal oak aromas and flavours).

Toasting

The degree and duration of the heating of the staves to bend them to shape has a profound effect on the flavour and structure imparted by the barrel. The firing process toasts the staves, not only to “light”, “medium” or “heavy” toast, but to all variety of levels in between. Most Australian winemakers use “medium” to “medium plus” toast.

The desired level of toast is not simply a question of how much toasty flavour the winemaker is looking for. Toasting not only draws out the vanilla and coconut flavours of a barrel, but it provides a buffer between the alcohol in the wine and the tannins it draws out of the wood. The less a barrel is toasted, the more tannins and other wood characteristics are drawn out. Lightly toasted barrels therefore produce wines with more oak tannins, while wines in more heavily toasted barrels tend to be stronger in spicy, toasty oak flavours.

Burgundy barrels are generally more heavily toasted than Bordeaux, toning down oak tannins to accentuate the more subtle characters of pinot noir and chardonnay. With higher quality oak available today, winemakers are able to make exceptions. Kooyong’s Sandro Moselle is sourcing the tightest-grained oak he can get, allowing him to move away from heavy and medium toast to light toast for chardonnay.

The effect of toasting can be pronounced, and there may be just one minute of difference in toasting between different levels, and vast differences can exist within and between coopers. While working at De Bortoli, William Downie used a halogen light to inspect the inside of every one of 450 barrels received every year, to select the best for pinot noir. “I didn’t care what was written on the end of the barrel, didn’t care about the forest, didn’t care about the cooperage – I was looking for the quality of the staves and the consistency of the toast,” he says.

How do you like your toast?

Light toast                Fruity wines with less oak flavour and more oak tannin

Medium toast          Vanilla and coffee flavours. Less tannic, rounder, smoother and more persistent wines. Most commonly used in Australia.

Heavy toast              Roasted coffee bean, toasted bread, clove and smoked meat characters, with less tannins

What does oak contribute to wine?

Lactones
The most important oak-derived flavour in wine, responsible for coconut, spicy, earthy and herbal oak aromas and flavours, higher in concentration in American oak. Toasting may increase these flavours, though particularly high toast and open-air seasoning can decrease them.

Vanillin
Open air seasoning increases the level of vanillin, as does toasting (although very high toast levels can decrease it). Barrel fermentation can significantly reduce its level.

Giacol
The smoky aromas derived from barrel toasting increase at higher levels of toast.

Volatile phenols
The spice-like roasted character, reminiscent of aromas ranging from clove to smokiness, even carnation, is only present in toasted wood, and decreases with seasoning.

Terpenes
The essential oils of fruit, tea and perfume are more prominent in American oak than French.

Furfurals and maltol
Caramel, butterscotch and bitter almond flavours from toasting wood sugars increase with higher levels of toasting but decrease with very high toast. The action of yeasts during barrel fermentation can transform these into smoked meat or leather characters.

Tannins
Colour and astringency imparted by tannins protect the wine from oxidation and reduction effects. Their concentration decreases with heavy toasting.

Roll out the barrels

The larger the oak vessel, the lower the ratio of surface area to volume, hence smaller barrels impart more oak flavour and tannin and more oxygen interchange. Larger barrels are also made with thicker staves, further reducing oxygen movement. These factors have prompted a recent trend toward larger barrels in Burgundy and across Australia.

At Vasse Felix, Virginia Willcock ferments and matures her flagship Heytesbury Chardonnay in a high 70-80% new oak, without any overpowering wood character in the wine. “It’s about finding beautiful oak,” she explains. “We were buying barrels made for cabernet and using them for chardonnay, but now we’re sourcing barrels made specifically for chardonnay from Burgundian coopers.”

Types of barrels

Feuillette*                      132L                       Traditional Chablis barrel, increasingly rare, except for topping up larger barrels.

Bordeaux barrique       225L                      The most famous barrel format, with thin staves, commonly used in Australia.

Champagne pièce*       205L                      Burgundy pièces are more common in Champagne today.

Burgundy pièce            228L                       Squat barrel for smaller cellars, with thick staves and a deeper bilge for lees accumulation. Burgundy barrels generally have thicker staves than Bordeaux, to decrease the oxygenation of the more sensitive pinot noir and chardonnay.

Hogshead                       300L                      Originated in Cognac and now common across the New World. Popular in Australia.

Puncheon                       450-500L              Larger barrel, increasingly popular in Burgundy and New World countries.

Demi-muid                     500-600L             Large barrel of Châteauneuf-du-Pape.

Tonneau*                       900L                       Four Bordeaux barriques, no longer used.

Fuder                               1000L                    Typical on the Mosel in Germany.

Foudre                             2,000-12,000L    Large vat, used in Alsace and Champagne.

Cuve or vat                     5,000-30,000L    Very large fermentation or storage vessel.

Old barrels

The newer the barrel, the more wood flavour and tannin it can impart and the greater the rate of oxygen interchange. As barrels get older, tannins and flavours are leached out and oxygen movement decreases as the pores are clogged. As Australian winemakers increasing seek more subtle oak influence, older barrels are more highly prized. De Bortoli uses its cheaper Gulf Station and Windy Peak wines to season new barrels for a couple of vintages before they are used for its premium Yarra Valley wines.

Even the age of a new barrel can make a difference. “Firing a barrel is like roasting coffee,” compares William Downie, who throws away coffee beans when they’re two or three weeks old. “If you fire a barrel in France and ship it to Australia, it’s dead before you use it,” he says. He now has an agreement with a local cooper to fire a barrel on the day he requests and ship it to his winery in 24 hours. He upholds this as more important for his William Downie Pinot Noirs than anything else. “Everyone else cares about the forests, but we’ve started using reject staves. While others look for tight grain, we prefer the broadest grain we can find.”

Time in barrel

Wines may spend as little as two months in wood or as much as four years. The famous Vega Sicilia in Spain’s Ribera del Duero has matured its red wines for up to ten years in barrel. The trend in Australia is to get wines out of barrel sooner, often in less than twelve months, to preserve fruit integrity and avoid the wines drying out.

Barrel fermentation

Fermenting a wine in barrel produces a softer, less obvious and more integrated oak flavour. Yeast acts on the highly aromatic oak flavours to reduce their impact. A barrel also naturally regulates temperature during fermentation better than a large tank.

Other types of wood

Wine barrels have been made from acacia, cypress, chestnut, ash, redwood, pine, eucalyptus and poplar, though these tend to be more porous than oak and hence produce overwhelming flavours and harsh tannins. Barrels from these woods are rare and some are not currently legal in Australia.

Beyond barrels: Oak alternatives

“Adjuncts” is the name given to oak alternatives other than barrels. By submersing oak chips, shavings, “beans”, “briquettes” or staves in stainless steel tanks, substantial cost savings can be realised, potentially one-twentieth the cost of a new American oak barrel. The use of adjuncts has exploded in Australia over the past decade, particularly in wines under $20.

“We’re certainly using fewer barrels in our wineries than we used to,” says Treasury Wine Estates’ Sam Glaetzer. “By using planks we can achieve the characteristics of old oak, while keeping the wine in stainless steel tanks.” The popular and value-for-money Mike Press Shiraz uses a combination of second-hand barrels with oak sticks in muslin bags, submersed like tea bags.

A decade ago, the use of oak in this way wasn’t even an option for a winemaker. While these techniques will never compete with the best barrels, they can be better than poor barrels in imparting oak flavour, aroma, tannin and colour stability without oxygen interchange. Once made only from leftover wood scraps, adjuncts are improving, often purpose-made from higher quality wood and seasoned and toasted in a similar way to barrels.

Tyson Stelzer