Oak Aging and Wine
Most of us
know that the majority of fine wines are aged in oak barrels. But
why? What are the advantages? Are there any disadvantages? Are
there different kinds of oak? Why are they different? What do
these differences mean? Whats it all about?
Aging Wine Before It is Bottled
After fermentation is completed and
wine is racked several times to remove the largest solids, the
young wine is usually rough, raw and green and needs
to settle for a period of time. This aging can be done in neutral
containers such as stainless steel, cement lined vats, old large
casks, etc. or it can be done in small relatively new wood
barrels which are not neutral, but which will influence the
Oak Barrel Influence - the basics
Subtle flavors are imparted to wine as
it ages in the barrel. Different types of oak (French and
American being the two most widely used) from different regions
(Limousin, Nevers, Troncais, etc.) give differing levels of
flavor to the wine (most often described as vanilla).
Wine, as it rests in the barrel, goes through
subtle chemical changes, resulting in greater complexity and a
softening of the harsh tannins and flavors present at the end of
fermentation. The effect of specific wood on different wines is
the subject of great discussion and experimentation among wine
makers throughout the world.
A barrel essentially does two things: it allows
a very slow introduction of oxygen into the wine; and it imparts
the character of the wood into the wine. (This diminishes as a
barrel gets older. You usually get 50% of the extract that a
barrel has on the first use, 25% the second and less after that.)
About Barrels: Why and How They Enhance Wine
(Courtesy of Simi Winery, Healdsburg, California)
origins of barrels for wine storage
Most of us are familiar with museum
specimens and replicas of archeologically-recovered clay pots and
amphorae from Greek and Roman sites: these clay-based vessels
predate wooden containers for storage of wine and other liquid
goods. But the existence of straight-sided, open wooden buckets,
employing the craft of the cooper, is documented in Egypt as
early as 2690 BCE (Before the Christian Era). Fully-closed
barrels were first developed during the Iron Age (800-900 BCE),
and by the first century BCE were widely in use for holding wine,
beer, milk, olive oil, and water.
As trade and transportation developed, shippers
discovered that sealed wooden containers were vastly superior to
relatively fragile clay vessels, and the craft of cooperage --
barrel-making -- was launched, developing in direct proportion to
the growth of trade. Wooden casks of barrels had largely replaced
their clay counterparts by as early as the second century CE .
The most significant advantages of wooden
barrels were, first, their strength: being made of wood and set
round with hoops (first also made of wood, later of metal) that
bound the joints of the barrels into a double arch; second, the
barrels themselves were like wheels and could be easily rolled
from one resting place to another; third, it became evident that
certain goods - like wine - actually benefited from being stored
This third advantage forms the basis for the
entire modern cooperage industry, and in fact is the only real
reason for its continued existence in a world where stainless
steel and non-reactive synthetic materials outweigh all other
advantages that barrels ever possessed.
Why do we still use barrels?
If the practice of using wooden barrels for
wine storage had not been common throughout the long period of
years when wooden barrels were the only practical containers for
wine, it is highly unlikely that todays vintners would ever
have thought of adding the dimensions of oak flavor to their
wines. So we may say that it is a happy, historical coincidence
that wine and wood marry together to form a richer, more complex
flavor and texture than wine would have were it stored in a
totally non-reactive container.
Now, what does an oak (and oak is -- almost
without exception -- the only kind of wood used for fine wine
storage) barrel impart to wine that improves and enhances it?
Well look at two ways that wine benefits from its contact
First, for red wines, controlled oxidation
takes place during barrel aging. This very gradual oxidation
results in decreased astringency and increased color and
stability. It also evolves the fruit aromas to more complex ones.
Through a program of topping the wine (filling up the barrel)
while it is in the barrel and racking the wine from barrel to
barrel to clarify it, just enough oxygen is introduced to the
wine to have these beneficial effects over a period of many
Second, oak wood is composed of several classes
of complex chemical compounds, each of which contributes its own
flavor or textural note to both red and white wines. The most
familiar of these are vanilla flavors, sweet and toasty aromas,
notes of tea and tobacco and an overall structural complexity of
tannin that mingles with the tannin from the fruit itself (in the
case of red wines). The specific compounds creating these
delightful nuances in the finished wine are: volatile phenols
containing vanillin; carbohydrate degradation products containing
furfural, a component yielding a sweet and toasty aroma;
oak lactones imparting a woody aroma; terpenes to
provide tea and tobacco notes, and
hydrolysable tannins which are important to the relative
astringency or mouth feel of the wine.
The chemistry of the oak barrel can impart
differing amounts and qualities of flavor and texture depending
upon the barrel manufacturing techniques and type of oak used.
American oak (Quercus alba) versus French oak (Quercus robur),
sawn versus hand-split, air-drying vs. kiln drying of the staves,
and the use of boiling water, steam, natural gas, or wood fire to
bend the staves are among the most important variables in the
manufacturing process. As you can imagine, the barrel makers and
wine makers all over the world hold widely differing opinions on
the best way to make a barrel! One thing we can all agree on is
that barrel making is an extremely complicated craft - there are
no amateur barrel makers!
The Coopers craft
The word cooper originates from the
barrel makers of Illyria and Cisalpine in Gaul, where wine was
stored in wooden vessels called cupals, and the maker
was a cuparius. If your surname is Cooper
or Hooper you can bet that some of your ancestors
were employed in the time-honored craft of cooperage.
Organized coopers guilds originated in
Rome well before the Christian Era. They grew and flourished
throughout medieval Europe and reached the apex of their
membership in the late 19th century, before dwindling rapidly in
the years following World War I, as other materials, first metals
and then synthetics, replaced the wooden vessels formerly used
throughout the household for washing, churning, eating, cooking,
To understand why this profession is so highly
skilled and specialized -- with an apprenticeship even today of
seven years duration -- lets go through the steps
required to make a wine barrel. Keep in mind that both the
procedure and the tools have remained relatively unchanged for
the past three thousand years.
make a wine barrel
First, get yourself a tree. Not just any tree of course.
Cutting down that messy sycamore in the front lawn that has been plaguing you
since you moved in won’t work. You’ll need a Quercus robur, one of the more
than four hundred species of oak trees that grow around the world. The Quercus
robur can easily be found in central and eastern France, where they are grown in
government-owned and managed forests, and where you can purchase one at a
periodic auction. You will want a tree from a forest located in a cool climate,
where the tree grows slowly, thus producing a wood with a tighter grain than
those that grow more quickly in the region of Limousin. So you should do your
shopping in the forests of Troncais, Allier, Nevers, or Vosges. There are other
sources for good oak, such as Slavonia and even Russia, but the most prestigious
barrels are made from French wood.
The forest should be planted with very close spacing, a condition that promotes
tree growth with straight grain and no knots. These differences in tree
structure produce noticeable differences in tastes imparted to the finished
wine, and are an important part of how a winery achieves its ultimate style
goals for each wine fermented and/or aged in barrels.
want your tree to be at least 100 years old for your purpose, with a straight,
unblemished trunk, about five feet in circumference. It doesn’t really matter
how tall the tree stands, because you’ll be using only the part that extends
from the ground to the first lateral branches, and if you do a good job, you
should get at least 2 and at most 4 barrels from your tree.
Next, you’ll need to measure the tree trunk into usable
lengths for the barrel staves. Staves are the narrow strips of wood that are
formed into the holding sides of the barrel. You have a choice of making either
a Burgundian barrel (piéce) or a Bordeaux barrel (barrique). Both shapes of
barrel will hold approximately 60 gallons of wine. The slight differences in
shape and size between the Burgundian and the Bordeaux barrels don’t seem to
have any definitive reason except that of tradition.
It may be that because most Burgundian cellars are
underground, the barrels work better if they are slightly rounder and therefore
roll more easily and are shorter to fit better through inside doorways. Or it
may be that white wines fermented in Burgundian barrels have more sediment
collect in them from the lees (expended yeast cells) and that the bigger bulge
in the barrel concentrates the sediments more effectively. But type of wood and
method of making are the same for both piéce and barrique.
At Simi, Burgundian or Bordeaux-shaped barrels will be used at
our Winemaker’s discretion for Chardonnay, Cabernet Sauvignon, or Sauvignon
Blanc. His/her choice is based on the particular style characteristics each
cooperage imparts to its barrels. For instance, if a certain lot of grapes has
good ripe fruit character but not much spiciness, he might use a François Fréres
barrel (piéce) to add that dimension. For wine that lacks length of finish, he
may use a Taransaud (barrique), and for wine that needs more weight on the
palate to be well balanced, he might choose a Damy barrel (piéce). Each lot of
wine, be it red or white, will be enhanced in balance and enriched in flavor and
structure by the barrel in which it is fermented and/or aged. But a barrel that
begins its life with white wine in it always will be used for white wine, and
the same for red wine barrels. Never the two shall mix!
You will have to hand split the logs into halves, then
quarters, then eighths, and finally into the exact stave size. You could get
twice as many useable staves if you were to saw the logs, but this tends to
raise the tannin and astringency of the oak to an unacceptably high level.
You can take a break now, because you'll need to allow the
hand-cut rough staves to dry for three to five years in the open air. Open-air
drying (as compared to the more rapid kiln drying) decreases the possibility of
barrel leakage, and leaches more tannins from the wood, resulting in a softer,
finer finished wine. Although the wood must dry, it will be rotated on the stack
of rough staves and periodically sprinkled with water so that the final level of
humidity in the wood is about 15 per cent. Now you have good air-dried rough
Now that you have good, air-dried rough staves, you can begin
to form the finely finished staves. You’ll cut them to a precise length and
taper them at the ends, so that they fit together snugly when the barrel is
curved into shape. Then you’ll hollow out the inside flat part of the stave.
To assemble the barrel itself, you’ll fit the staves onto a frame, and then
arrange the staves around an iron hoop. The barrel at this stage resembles a
teepee, splaying out from the hoop at the top. In order to shape the barrel, you
must bend the staves so that they can, in turn, be bound into another iron hoop
at the bottom. Simi prefers that you use an open fire of oak wood chips rather
than boiling water, steam or a gas fire. The wood chip fire helps provide a
toasty flavor to the wine that will age in the barrel. You'll toast the barrel
without a lid on it for about 40 minutes at 320 - 325 F. But these are just
guidelines: Coopers toast barrels according to their own sense of what will be
best, because each cooper has the expertise to extract the best possible
You’ll custom make flat ends for your barrel and fit them
into grooves at top and bottom of the side staves. Next, remove the temporary
hoops, and set permanent ones into place. Then scrape and sand the barrel, so
that the exterior is smooth. Now pour cold water into the barrel, and add air
pressure to test for leaks. Finally, imprint the barrel proudly with your
cooper’s brand, and send us a bill for - depending upon the rate of exchange -
550 to 650 dollars.
When your barrel arrives at the winery
Your barrel’s life has just begun when it arrives at the
winery. It will probably be one of a ship’s container load of 150 barrels, and
will reach the winery between June and August. Your barrel has arrived with its
bung hole (opening in the side for the wine to be moved in and out) sealed by a
wooden bung and a piece of burlap. This prevents contamination from entering the
barrel while allowing for enough air transfer to keep the inside of the barrel
fresh and dry.
No matter how much care you’ve taken in making your barrel,
we will still do a thorough inspection of each barrel that we receive. It is
essential to make sure that the barrel is sound - it should smell good and be
clean inside. The wood inside, both for toast level and smoothness of finish
must meet our expectations, and of course, it must be completely tight so that
it will never leak.
All incoming barrels are subjected to two different kinds of
inspection. The first is one in which our Cellarmaster tests the structural
integrity of your barrel by checking the fit and finish, stave length and
thickness, bung hole size and fit and by noting any external cracks or
Our Enologist then scrutinizes the inside of every barrel in
the shipment, to make sure that you’ve toasted your barrel to the level that
we’ve specified (light, medium, or heavy), to see if there are any blisters or
char caused by overheating or excessive humidity during the toasting process,
and to inspect the wood grain consistency and tightness of fit. He also checks
to see if you have used any paste or reeds (the plant material used between the
staves in the ends of the barrel) to repair small cracks or holes and to
determine if the reeds are intact. Finally, he notes any uneven planing on the
inside or any internal knots.
Your barrel has passed the test! Now we will mark the barrel
to identify the varietal and the vineyard origin of the wine that will be stored
in the barrel, as well as a complete history of any and all treatment given to
the barrel during its life at Simi. Then we stencil the barrel with a cooperage
designation and the year the barrel was delivered.
When the crush begins, and grapes come into the winery to be
pressed and fermented (Chardonnay and Sauvignon Blanc) or fermented and then
pressed (Cabernet Sauvignon), the cellar crew goes into action, rinsing the
barrels and soaking the heads (end pieces). Then they pump five or six gallons
of hot water into the barrel and seal it with a silicone bung. After rotating
the barrel to each end for about twenty minutes, they pull the bung. If the
barrel is completely liquid tight, a vacuum should have been created as the
water cooled, and an audible rush of air will prove that your barrel is sound.
Your barrel is now filled with wine (Cabernet Sauvignon) or
juice for fermentation (chardonnay or Sauvignon Blanc) and from this time on,
will undergo a regular, rigorous program of monitoring by the Cellarmaster for
the rest of its useful life. These programs of inspection and cleaning, both
while the barrel contains wine and when it rests empty before another harvest,
ensure that your barrel continues to enhance the wine and that it never develops
any problem that could impair the quality of the wine.
But nothing lasts forever, not even a well-made barrel. At
Simi, we use white wine barrels for six or seven years and red wine barrels for
five years. After that time, the oak has little or no beneficial flavor
components left to impart to the wine, and the barrel becomes essentially a
neutral container. But it is still a sound container for wine, and we usually
sell it to some other winery who wishes to use it for storage purposes. The
final phase in your barrel’s life is when your barrel is cut in half and sold
for flower planters, at about ten dollars per planter.
But although your barrel is no more, the wine that was aged in
it is still being enjoyed, and the connoisseur taster is exclaiming about its
rich notes of toast, vanilla, almond, caramel, and clove. These are all nuances
of complexity added to the wine from the barrel you made so many years before.
Oak - Chemical Structure and Its
Effect on Flavor
[Many of the best wines are
fermented and/or aged in oak barrels. The barrels can be large or small, old or
new, or a combination of these factors. The smaller the barrel, the newer the
barrel, and the more time spent in the barrel, the more oak flavors will be
imparted into the wine. The source of the wood is also very important. Barrels
are made by cutting wood into long, narrow pieces called staves. After
seasoning, the staves must be heated so they can be bent to form the barrel.
Steaming is the cheap method. The best method is to expose them to a flame. The
longer the flame exposure, the more toasted or charred the wood becomes. This
greatly affects the flavors imparted to the wine. The following information is
from World Cooperage (www.worldcooperage.com), makers of oak barrels. Barrel
production is science as well as art.]
Wine making has enough mysteries. That’s why we’ve taken great steps to
understand the various species of oak and the role they play in winemaking.
THE COMPOSITION OF OAK AND ITS
Tannin - [We tend to think of tannins in wine as coming from
the skins, pits, and stems of the grapes, but in fact some comes from the oak
barrels in which the wines are aged.] While tannins are approximately 1% of
American oak and 8% of French oak mass, they play a vital role in [wine] aging.
Hydrolysable, heat sensitive tannins stored in the tree’s radial rays, are
controlled by seasoning regimes, bending techniques, toasting times, and
toasting temperatures. Today, precise oak tannin levels are achievable thanks to
Lignin --> Vanillin - A family of compounds, notably
vanillin, is released during oak lignin breakdown. Slowly, nature’s elements
including precipitation, ultraviolet rays, and fungi, break down lignin.
Toasting accelerates the degradation. Scientific understanding of these
processes allows for more precise flavors.
Cellulose - The most abundant, natural polymer on Earth,
cellulose is nearly 50% of white oak, but plays only a small part in aging wine.
It is important because it holds the wood together.
Hemicellulose --> Wood Sugars/Body - Air seasoning initiates
the polymer’s breakdown into simple sugars. As oak climbs through 300 F during
toasting, more simple sugars form. Caramelized sugars and sweet-associated
aromas then develop. Toasty characters develop as the oak passes 420 F. Using
this research, controlling temperatures allows definable, repeatable flavors.
THE STRUCTURE OF OAK AND ITS CONTRIBUTION TO FLAVOR
French Oak (the fragile sessile oak Quercus petrae Liebl.) -
When examining French oak, we find the highest tannin of the oak types. Wine has
easy access to an array of compounds in the more porous sessile oak, providing
multiple extractives. An example is the popular spice notes that stem from
extractives such as caryophyllene and copaene. Structurally, one finds less
tyloses. Hand splitting following the grain is required. Logs sourced from the
Office National des Forêts make for more expensive timber. This results in a
more expensive barrel that is appreciated by winemakers for its flavor
characteristics rather than its price.
American Oak (the strong Quercus alba) - Structural differences
in American oak’s hemicellulose and lignin result in more intense vanilla,
wood sugars, and toastiness. Because stave timber is purchased from private
landowners, log costs are lower. Its density, high tyloses, and straight grain
means higher yields, machine cutting, and lower cost barrels with popular
Eastern European (Slovenian & Hungarian) Oak (the slow
growth Quercus petraea Liebl.) - Under a microscope, this sessile oak is
structurally similar to what is found in France, yet it has slightly different
qualities including less tannin. These trees grow more slowly and are smaller,
creating fine grain and extremely subtle extraction. Research shows that its
hemicellulose breaks down more easily, forming a different spectrum of toasty
aromas. Eastern European oak is purchased from both government controlled
forests and private land. Although the logs are less expensive, lower yields
produce barrels that are about average in cost.
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