History
In early
wine history, the amphora was the vessel of choice for the storage
and transportation of wine. Due to the perishable nature of
wood material it is difficult to trace the usage of barrels
in history. The Greek historian Herodotus noted that ancient
Mesopotamians used barrels made of palm wood to transport wine
along the Euphrates. Palm is a difficult material to bend and
fashion into barrels, however, and wine merchants in different
regions experimented with different wood styles to find a better
wood source.[2]
The use of oak has been prevalent in winemaking for at least
two millennia, first coming into widespread use during the Roman
empire. In time, winemakers discovered that beyond just storage
convenience that wine kept in oak barrels took on properties
that improved the wine by making it softer and in some cases
better-tasting.[3]
Robert Mondavi is credited with expanding the knowledge of winemakers
in the United States about the different types of oak and barrel
styles through his experimentation in the 1960s & 1970s.[4]
Effects
on wine
The effect
of oak aging on red wine color: the above samples are both
Penedes region Cabernet
Sauvignon varietals; on the left, a two-year-old cosecha;
on the right a six-year-old crianza. As the wine
matures, its color shifts from deep purple or crimson to
a lighter brick-red and takes on a more graduated appearance
in the glass.
The porous
nature of an oak barrel allows some levels of evaporation and
oxygenation to occur in wine but typically not at levels that
would cause oxidation or spoilage of the wine. In a year, the
typical 59-gallon barrel can lose anywhere from 5 to 6 gallons
of wine through the course of evaporation. This evaporation
(of mostly alcohol and water) allows the wine to concentrate
its flavor and aroma compounds. Small amounts of oxygen are
allowed to pass through the barrel and act as a softening agent
upon the tannins of the wine.[3]
The chemical
properties of oak itself can have a profound effect on the wine.
Phenols within the wood interact with the wine to produce vanilla
type flavors and can give the impression of tea notes or sweetness.
The degree of "toast" on the barrel can also impart different
properties affecting the tannin levels of the wine as well as
the aggressive wood flavors.[5] The hydrolyzable tannins present
in wood, known as ellagitannins, are derived from lignin structures
in the wood. They help protect the wine from oxidation and reduction.[6]
Wines can
be barrel fermented in oak or they can be placed in oak after
fermentation for a period of aging or maturation. Wine that
is matured in oak receives more of the oak flavors and properties
than wine that is fermented in oak. This is because yeast cells
interact with and "latch on" to the oak components. When the
dead yeast cells are removed from the wine as lees some of these
oak properties go with them.[7] A characteristic of white
wines that are fermented in oak include a pale color with an
extra silky texture. White wines that are fermented in steel
and then matured in oak will have a darker coloring due to the
heavy phenolic compounds that are still present.[8]
Flavor notes that are common descriptions of wines exposed to
oak include caramel, cream, smoke, spice and vanilla. Chardonnay
is a variety that has very distinct flavor profiles when fermented
in oak that include coconut, cinnamon and cloves notes. The
"toastiness" of the barrel can bring out varying degrees of
mocha and toffee notes in red wine.[9]
The length
of time that a wine spends in the barrel is dependent on the
varietal and style of wine that the winemaker wishes to make.
The majority of oak flavoring is imparted in the first few months
that the wine is in contact with oak but a longer term exposure
can affect the wine through the light aeration that the barrel
allows which helps to precipitate the phenolic compounds and
quickens the aging process of the wine.[8]
New World Pinot noir may spend less than a year in oak. Premium
Cabernet Sauvignon may spend two years. The very tannic Nebbiolo
grape may spend four or more years in oak. High end Rioja producers
will sometimes age their wines up to ten years in American oak
to get a desired earthy, vanilla character.[7]
Oak
types and sources
The species
of oak typically used for American oak production is the Quercus
alba which is a white oak species that is characterized by
its relatively fast growth, wider grains and lower wood tannins.
It is found in most of the Eastern United States as well as Missouri,
Minnesota and Wisconsin where many wine barrels are from. In Oregon
the Quercus garryana white oak has started to gain usage
due to its closer similarities to European oak. In France, the
main winemaking oak species is the Quercus petraea which
is known for tighter grain, high tannins and lower aromatics than
its American oak counterpart. French oak typically comes from
one or more primary forests: Allier, Limousin, Nevers, Tronais
and Vosges. The wood from each of these forests has slightly different
characteristics. Many winemakers utilize barrels made from different
cooperages, regions and degrees of toasting in blending their
wines to enhance the complexity of the resulting wine.[10]
Italian winemakers have had a long history of using Slavonian
oak from the Quercus robur which is known for its
tight grain, low aromatics and medium level tannins. Slavonian
oak tends to be used in larger barrel sizes (with less surface
area relative to volume) with the same barrels reused for
many more years before replacement.[11]
Prior to the Russian Revolution, Quercus petraea
oak from the Baltic states was the most highly sought after
wood for French winemaking.[12]
Today Russian oak from the Adygey region along the Black
Sea is being explored by French winemakers as a cheaper
alternative to French oak.[13] Canadian wineries have been
experimenting with the use of Canadian oak, which proponents
describe as a middle ground between American and French
oak even though it is the same species as American oak.[14]
Oak trees
are typically between 80-120 years old prior to harvesting with
the ideal conditions being a cool climate in a dense forest
region that gives the trees opportunity to mature slowly and
develop a tighter grain. Typically one tree can provide enough
wood for two 59 gallon barrels. The trees are typically harvested
in the winter months when there is less sap in the trunk.[12]
Differences
in French and American oak
American
oak tends to be more intensely flavoured than French oak with
more sweet and vanilla overtones due to the American oak having
two to four times as many lactones.[9]
Winemakers that prefer American oak (including a long tradition
for Spanish winemakers) typically use them for bold, powerful
reds or warm climate Chardonnays. Besides being derived from
different species, a major difference between American and French
comes from the preparation of the oak. The tighter grain and
less watertight nature of French oak encourages coopers to split
the wood along the grain rather than saw. French oak is then
traditionally aged or "seasoned" for at least two years whereas
American coopers will often use a kiln-dry method to season
the wood.[12]
Long periods of outdoor season has a mellowing effect on the
oak that kiln-dry methods have difficulties replicating.[9] The sawing, rather than splitting,
of American oak also enhances the differences between the two
styles due to the rupture of the xylem cells in the wood which
releases many of the vanillin aromatics and lactones responsible
for characteristics like the coconut notes.[15]
Wine
barrel
The
"red band" on some wine barrels is the residue of spilt
red wine. For aesthetics some wineries will paint this center
portion of the barrel red for a cleaner look.
Wine barrels,
especially those made of oak, have long been used as containers
in which wine is aged. Aging in oak typically imparts desirable
vanilla, butter and spice flavors to wine. The size of the barrel
plays a large role in determining the effects of oak on the
wine by dictating the ratio of surface area to volume of wine
with smaller containers having a larger impact. The most common
barrels are the Bordeaux barriques style which hold 59 gallons
(225 liters) followed by the Burgundy style barrel which hold
60 gallons (228 liters). Some New World wine makers use the
large hogshead 79 gallon (300 liter) size.[8]
New barrels
impart more flavors than do previously used barrels. Over time
many of the oak properties get "leached" out of the barrel with
layers of natural deposits left from the wine building up on
the wood to where after 3 to 5 vintages there may be little
or no oak flavors imparted on the wine.[5] The cost of barrels varies
due to the supply and demand market economy and can change with
different features that a cooperage may offer. As of late 2007
the price for a standard American oak barrel was $270 USD, French
oak $600 USD, and Eastern European $480 USD.[16] Due to the expense of barrels,
several techniques have been devised in an attempt to save money.
One is to shave the inside of used barrels and insert new thin
inner staves that have been toasted.[17]
Barrel
construction
Barrels
are constructed in cooperages. The traditional method of European
coopers have been to hand split the oak into staves (or strips)
along the grain. After the oak is split it is allowed to "season"
or dry outdoors while exposed to the elements. This process
can take anywhere from 10 to 36 months during which time the
harshest tannins from the wood are leached out. These tannins
are visible as dark gray and black residue left on the ground
once the staves are removed. The longer the wood is allowed
to season the softer the potential wine stored in the barrels
may be but this can add substantially to the cost of the barrel.
In some American cooperage the wood is dried in a kiln instead
of outdoor seasoning. While this method is much faster, it doesn't
soften the tannins quite as much as outdoor seasoning.[18]
The staves
are then heated, traditionally over an open fire, and when pliable
are bent into the shape of the desired barrel and held together
with iron rings. Instead of fire, a cooper may use steam to
heat up the staves but this tends to impart less "toastiness"
and complexity to the resulting wine. Following the traditional,
hand worked style a cooper is typically able to construct one
barrel in a day's time. Winemakers can order barrels with the
wood on the inside of the barrel having been lightly charred
or “toasted†with fire, medium toasted, or heavily toasted.[18] Typically the "lighter" the
toasting the more oak flavor and tannins that are imparted.
Heavy toast or "charred" which is typical treatment of barrels
in Burgundy wine have an added dimension from the char that
medium or light toasted barrels do not impart.[8]
Heavy toasting dramatically reduces the coconut note lactones,
even in American oak, but create a high carbon content that
may reduce the coloring of some wines. During the process of
toasting, the furanic aldehydes in the wood reach a higher level
of concentration. This produces the "roasted" aroma in the wine.
The toasting also enhances the presences of vanillin and the
phenol eugenol which creates smokey and spicy notes that in
some wines are similar to the aromatics of oil of cloves.[15]
Barrel
alternatives
Although
oak barrels have long been used by winemakers, many wineries
now use oak wood chips for aging wine more quickly and also
adding desired woody aromas along with butter and vanilla flavors.
Oak chips can be added during fermentation or during aging.
In the latter case, they are generally placed into fabric sacks
and placed into the aging wine. The diversity of chips available
gives winemakers numerous options. Oak chips have the benefit
of imparting intense oak flavoring in a matter of weeks while
traditional oak barrels would need a year or more to convey
similar intensity. Critics claim that the oak flavoring from
chips tend to be one-dimensional and skewed towards the vanilla
extract with the wines still lacking some of the physical benefits
that barrel oak imparts.[17] The
use of oak powder is also less common than chips, although they
are a very practical alternative if oak character is to be introduced
during fermentation. Oak planks or staves are sometimes used,
either during fermentation or aging. Wines made from these barrel
alternatives typically do not age as well as wines that are
matured in barrels.[8]
Improvements in micro-oxygenation have allowed winemakers to
better mimic the gentle aeration of oak barrels in stainless
steel tanks with oak chips.[19]
Prior to
2006, the practice of using oak chips was outlawed in the European
Union.[20] In 1999, the
Bordeaux court of appeals fined four wineries, including third
growth Chateau Giscours, more than $13,000 USD for the use of
oak chips in their wine.[21]
Other
wood types
Throughout
history other wood types, including chestnut, pine, redwood,
and acacia, have been used in crafting winemaking vessels, particularly
large fermentation vats. However none of these wood types possess
the compatibility with wine that oak has demonstrated in combining
its water tight, yet slightly porous, storage capabilities with
the unique flavor and texture characteristic that it can impart
to the wine that it is in contact with.[22]
Chestnut is very high in tannins and is too porous as a storage
barrel and must be coated with paraffin to prevent excessive
wine loss through evaporation. Redwood is too rigid to bend
into the smaller barrel shapes and imparts an unpleasant flavor.
Acacia imparts a yellow tint to the wine. Other hardwoods like
apple and cherry wood have an off putting smell.[23]
Austrian winemakers have a history of using Acacia barrels.
Historically, chestnut was used by Beaujolais, Italian and Portuguese
wine makers.[24]
Some Rhone winemakers still use paraffin coated chestnut barrels
but the coating minimizes any effect from the wood making its
function similar to a neutral concrete vessel. In Chile there
are traditions for using barrel made of rauli wood but it is
beginning to fall out of favor due to the musky scent it imparts
on wine.[25]
See Also:
Home
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Science of Wine Aroma
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Polyphenols
(Tannins) in Wine
Oak
in Wines
The Basic Wine Pairing Rules
Science of Food and Wine
Pairing
Sugars
in Wine
About
Wine Tasting
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Tasting Terms
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References
