All About Oak Barrels: Why And How It Enhances Wine

All About Oak Barrels Why And How It Enhances WineBarrels were first designed for storage of wine.  Many people have seen the museum specimens and replicas of amphorae and clay pots recovered by archeologists digging in Greek or Roman sites.  Such vessels predate wooden storage containers used for barrel aged wine and other liquids.  The existence of open wooden buckets with straight sides, using rings to hold slats together is documented as early as 2690 BCE (Before common era) in Egypt.  It was not until the Iron Age (900-800 BCE) that fully closed barrels were developed.  By the first century BCE, these barrels were often used to hold beer, wine, olive oil, milk and water.  With the development of transportation and trade, shippers found sealed wooden containers to offer many superior advantages to shipping in fragile clay vessels, and thus the craft of barrel making (known as cooperage) was launched and developed to meet the growth in trade.  Wooden casks or barrels had replaced the clay vessels early in the second century CE (Common Era).

The first reason for the growth of the use of wooden barrels was for the strength they provided.  Most were made of wood, held together using metal hoops, although the first were held together with leather.  The hoops bound the joints in a double arch.  Since the barrels were sealed and round, they could easily be rolled from one location to another for easier transportation.  Soon a third advantage was found.  Certain goods, such as wine receive benefits from being stored in a wooden vessel.  This advantage is the reason the modern cooperage industry continues to exist and was the only real reason it continued to exist in a world with stainless steel and other synthetic materials that do not react outweigh the benefits of the wooden barrel in all other categories.

Why are wooden barrels still used?  If the use of wooden barrels to store wine had not been made common through the many years when the only practical way to store large amounts of wine, it is not likely that vintners of today would have considered adding the flavor and dimensions of oak flavor to their wines.  In other words, it is a happy coincidence that wood is used to improve the flavor of wine, providing a more complex texture and flavor than if the drink were stored in a container that is totally nonreactive.  What is it that an oak, the only type of wood used in storage of fine wines, almost without exception, imparts to the wine to improve and enhance it.

Wine benefits from storage in oak wooden barrels in two ways.

  1. For the red wines, barrel aging offers controlled oxidation.  This gradual process can help to decrease the astringency while also increasing the stability and color of the wine.  It allows the fruit aromas to evolve into more complex ones.  By using a program of topping with wine or filling the barrel while it is in the barrel and then racking the wine out of one barrel and into another for clarification, there is just enough oxygen added to the wine to provide these effects over several months.
  2. Second, inside the oak there are several classes of complex chemicals each that can add to the flavor and textural not to both white and red wines.  Most familiar include the vanilla flavors, notes of tea or tobacco, sweet and toasty aromas and the overall structural complexity offered by tannin, which mingles with tannin from the fruit used in making red wine.  These compounds add delightful nuances in a finished wine.  They include volatile phenols that contain vanillin, degradation of carbohydrate products that contain furfural, components that yield a sweet and toasty aroma, oak lactones that impart a woody aroma, terpenes that provide the tobacco or tea notes, and hydrolysable tannins that are essential to the mouth feel or astringency of the wine.

The chemistry of the oak barrel selected can impart different qualities and amounts of texture and flavor, depending on the method of manufacturing it as well as the type of oak used.  American oak offers different flavors than French Oak.  If the slats are sawn it provides a different result than if it were sawn.  Staves that are air dried are different from those dried using the heat of a kiln.  Even the method of bending the staves provides important variables in the manufacturing process.  Every winemaker around the world seems to hold an opinion as to the best type of processes in manufacturing a barrel to add the best flavor to the wine.  However, all agree is that barrel making is a complex craft and there are no amateurs in the craft.

The Craft of the Cooper

The term cooper traces back to barrel makers of Cisalpine and Illyria in Gual.  There, wine was stored in wooden vessels referred to as cupals and the maker was called a cuparius.  Anyone with the surname of Hooper or Cooper probably can find ancestors who spend their days working in the ancient craft of cooperage.  Guilds of coopers organized first in Rome years before the birth of Christ.  They flourished and grew throughout medieval Europe, reaching their apex in membership in the late 1800s, but dwindled rapidly in the time following WWI, as other materials, including metals and later synthetics began to replace wooden vessels that were once used in many places in the home for washing, eating, choking churning and storage.  In order to better understand why the profession is so specialized and highly skilled, continuing to require a seven year apprenticeship today, consider the steps required in making a wine barrel.  The tools and procedure have remained virtually unchanged over the past three hundred years.

How Wine Barrels are Made

The cooper begins with the selection of the tree.  The tree must be the right species and most prefer the French oak Quercus robur, from the other 400 species of oaks that live on planet earth.  This particular species is easily found in eastern and central France, grown on government managed and owned forests and sold periodically at auction.  The best trees are from forests in cool climates that allow the tree to grow slowly, producing a tighter grain than trees which grow more quickly in Limousin.  Vosges, Nevers, Allier, and Troncais are the preferred forests.  Other good sources for this type of wood include Slavonia and even Russia, however the most prestigious barrels are created out of French oak.

For the best choices in wood, trees in the forest should be closely spaced, to promote growth of the wood with no knots and straight grain.  These differences in the structure of the tree create differences that are noticeable in the taste imparted to the finished wine.  They are an important factor in how the winery achieves its own goals for each wine that will be fermented or aged in the barrel.

The tree should be a minimum of 100 years of age, have a straight trunk free of blemishes and be approximately five feet in circumference.  Height is less important, as the only usable part in barrel making is that extending from the ground to the lowest lateral branch.  With careful planning each tree will make two to four barrels.

The next step is to measure the trunk into usable lengths for the oak barrel staves.  These are the narrow pieces of wood that form the sides of any barrel.  The cooper has the choice of creating a Burgundian barrel or a Bordeaux Barrel.  Either of the shapes is designed to contain approximately sixty gallons of wine.  The differences in shape and size between the two seem to have no definite reason other than that of tradition.

One explanation is that since most Burgundian cellars are located underground, slightly rounder barrels work better and roll easier.  The shorter size is also easier to fit through the inside doorways of the cellar.  A second possibility is that white wines, fermented in Burgundian barrels contain more sediment from the expended yeast cells or lees and a bigger bulge in the barrel is more effective at concentrating such sediments.  Regardless, the type of wood and the craftsmanship remain the same for either type of barrel that will be used to store wine.

At Simi, the choice between Burgundian or Bordeaux shaped barrels is left to the discretion of the winemaker for Sauvignon Blanc, Cabernet Sauvignon, or Chardonnay.  That choice is based on the particular style characteristics the cooperage imparts into the barrel  For example, if a certain batch of grapes offer better character as ripe fruit but lacks spiciness, the winemaker might select a François Fréres barrel to add dimension.  If it lacks the length of finish, the winemaker might use a Taransaud (barrique), and for wines needing more weight on the palate to provide better balance he might select a Damy barrel (piéce).  Each wine lot, whether red or white is enriched in flavor and enhanced in balance by the barrel selected for its fermentation or aging.  However a barrel that starts life with a white can only be used for whites and the same for red wine barrels.  This is one place where the barrels cannot be interchanged.

The logs are now hand split, first into halves, followed by quarters, eights and finally into the exact size of the stave.  While it is possible to double the number of usable staves by sawing the logs, this can increase the tannin and astringency of the barrel, often to a level too high to be acceptable.

At this point in the process, it is time to take a break, as the hand cut rough staves require three to five years of open air drying.  While drying could be accomplished faster in a kiln, speeding the process in this manner increases the chances that the barrel will leak and allows more tannins to be leached from the wood, causing the wine to have a finer, softer finish.  While the wood must dry, it is rotated on the stack of rough cut staves, and sprinkled with water periodically to keep the final level of the wood’s humidity at the 15% range.  This is essential to top quality air-dried rough staves.

Next, using these good quality, air-dried staves, it is possible to form finely finished staves that will be used to form the barrel.  Each stave will be cut to a precise length and tapered at the ends, allowing them to fit together snugly once the barrel is curved into its final shape.  Then the inside flat part of the stave is hollowed out.  For assembly of the barrel, the staves are fitted onto a frame and arranged around an iron hoop.  At this point in construction, the barrel resembles a teepee, with staves splaying out from the hoop at the top.  In order for the barrel to be shaped, the staves must be bent so they can be bound into a second iron hoop at the bottom.  Simi’s preference is that the cooper use an open oak wood chip fire instead of a gas fire, steam or boiling water.  The wood chips help to impart a toasty flavor to the wine that is going to age in the barrel.  The cooper will toast each barrel without the lid in place for 40 minutes at approximately 325 degrees F.  However, these are only guidelines.  Coopers develop their own sense of what will be best to toast the barrel in order to create the best of characteristics possible.

Next the cooper will make flat ends for the barrel and slide them into the grooves located at the top and bottom of the side staves.  The temporary hoops are then removed and permanent ones will replace them.  The barrel is scraped and sanded to create a smooth exterior.  Cold water is added into the barrel and air pressure is used to test for any leaks.  Each barrel is then proudly imprinted with the cooper’s brand.  A completed barrel cost depends on the exchange rate, but is normally between $550 and $650 US.

The Barrel Arrives at the Winery

The life of the barrel just begins once it arrives at a winery.  Normally, they are shipped in a container that includes about 150 barrels and arrives sometime between June and August.  The barrel will have the bung hole sealed using a wooden bung and burlap.  The seal is used to keep contamination from entering the barrel but allows enough air exchange to keep the barrel inside dry and fresh.

Regardless of the care of the cooper in creating the barrel, it will be thoroughly inspected when received at the winery.  It is essential that the barrel is sound.  It should be clean and smell good inside.  The inside of the wood that forms the barrel must meet standards for smoothness of finish, toast level and be completely tight so it has no possibilities of leaks.

Each incoming barrel is subjected to two different types of inspections.  The initial inspection is one in which the Cellarmaster tests the barrel for structural integrity by checking its fit and finish, length and thickness of staves, size of bung and fit and by checking for external splinters or cracks.

The Enologist then scrutinizes the inside of each barrel in the entire shipment to ensure that the barrel is toasted to the specified level (either light, medium or heavy), to ensure there are no blisters or char due to excess humidity or overheating during the process of toasting and to ensure the wood grain is consistent and tight in its fit.  He will also check to see if paste or reeds have been used in repairing any small cracks or other holes and to determine if the reeds used remain intact.  Finally, he will note any uneven planning inside the barrel or any internal knots.

Congratulations, your barrel has passed our inspection.  It will now be marked to identify the vineyard and varietal origin of the wine to be stored in the barrel, and keep a complete history of any treatments the barrel may receive during its life as a wine barrel at Simi.  Each barrel will be stenciled with its cooperage designation and the year it was delivered to the winery.  Once the crush starts, and grapes are brought into the winery for pressing and fermentation (for Chardonnay and Sauvignon Blanc) or fermented and the pressed (for Cabernet Sauvignon), the crew will move into action, rinsing the barrels, and soaking the end pieces or heads.  Then each barrel will have five to six gallons of hot water pumped inside and be sealed using a silicone bung.  Each barrel is then rotated end to end for approximately 20 minutes before the bung is pulled.  Barrels that are completely liquid tight should have created a vacuum as water cooled and there will be an audible rush of air proving it to be sound.

The barrel will be filled with wine or juice for fermentation.  Cabernet Sauvignon is fermented before going into the barrel, but Chardonnay and Sauvignon Blanc is fermented in the barrel.  From this point forward, the barrel will be regularly and rigorously monitored by the cellar master.  These programs of cleaning and inspection continue while the barrel is filled and when it is resting between harvests to ensure the barrel continues enhancing the wine and does not develop problems that might interfere with the quality of the wine stored in it.

Of course, nothing lasts forever, even the best made barrel.  At Simi, white wine barrels are used six to seven years and red wine barrels are replaced after five years.  After these time frames, the oak has few, if any beneficial flavor components that can be imparted to the wine and is essential a neutral container.  Since it is still a sound container for wine, it is usually sold to another winery wanting it for use as a storage container.  The final phase of the barrel’s life includes being cut in half and sold for use as a flower planter, normally at about $10 US per planter.

While your barrel is no more, the wine which aged in it can still be enjoyed by the connoisseur.  They will note the rich notes of clove, caramel, almond, vanilla and toast due to the hard work of the cooper.  These nuances of complexity are added by wine barrels that were individually manufactured years before.


  1. […] The history of casks begins in the 5th century BCE when the Greek historian Herodotus talks of casks of palm-wine being shipped to Babylonia. It seems likely that the cask significantly predates this and was first developed in the early Iron Age, around 800 to 900 BCE, perhaps even earlier. Certainly the art of bending wood via heat-application had been used in boat-making for millenia and the existence of straightsided, open wooden buckets, employing the craft of the cooper, is documented in Egypt as early as 2690 BCE. […]

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