AgEBB-MU CAFNR Extension

Green Horizons

Volume 21, Number 2
Spring 2017

Forest Products

White Oak, Whiskey, and Wine

By Hank Stelzer | MU Extension - School of Natural Resources

From scattered woodlots across northern Missouri and throughout the deep forests of the Ozarks, white oak (Quercus alba) stave logs are crafted into some 1.5 million-plus barrels annually that then find their way into the rack houses of some of America and Scotland's premier distilleries, and Napa Valley wineries.

In addition to Q. alba, coopers (barrel makers) can also use chinkapin (Q. muehlenbergii) and swamp white oak (Q. bicolor) to make what is known as tight cooperage (barrels) that do not leak.

The special anatomical structures these species possess that makes their barrels leak-proof are tyloses. These gum-like substances plug the early-wood pores of the heartwood and prevent the barrels from leaking.

The process of making a barrel begins where all other wood products begin; in the forest. White oak stave logs represent a small amount of the timber harvested in any one timber sale. It is generally less than ten percent on average in oak-hickory stands; the remainder of the harvested timber goes to grade lumber, flooring, railroad ties, pallets and blocking.

Suitable white oak stave logs range from 8 feet to 20 feet in length, at least 11 inches in diameter as measured inside the bark at the small end, and are fairly free of defects such as knots. Only veneer logs command higher prices than stave logs.

At the stave mill, logs are cut into approximately 39-inch lengths that are quartered lengthwise into four bolts. The quartered stave bolts are then sawn into flat, "quarter-sawn" stave blanks. Stave blanks are vary in width after defects are trimmed off the edges. Heading bolts (to make the top and bottom of the barrels) are about 20 inches long and are quartered from either larger-diameter logs or from stave bolts that have been trimmed of defects, such as knots.

Quarter-sawn stave bolts (left) are sawed into flat stave blanks and trimmed of defects. The blanks either go into header blanks for the top and bottom of the barrel (top right) or into stave blanks (lower right). The cross-section of each stave is a trapezoid and the wider in the middle to give the barrel its barrel shape.

Stave and header blanks for wine barrels are air-dried for 24 to 36 months to allow the tannins in the wood to break down, mellowing the oak in a manner that kiln-drying cannot replicate. Staves used in whiskey barrels, however, are commonly air dried for 30 to 40 days and finished in a dry kiln.

Header and stave blanks are planed to bring back the lighter color of the wood and help the finished barrel become more resistant to outside influences. After planing, the end user's address usually determines whether the barrel is assembled in Missouri or not. It all has to do with transportation costs. If you think about it, you can pack more wine barrel 'kits' on a semi destined for the Napa Valley or in a container for oversea markets compared to finished barrels. But, whether in the Show-Me State or in some far away cooperage, the process is basically the same.

To make the headers, a machine drills holes into the sides of the header planks and inserts wooden dowel pins on one side. The boards are then doweled together to a square shape of flat oak wood. No glue is used as this would impart unnatural flavors to the spirits and wine. This square is then cut into a perfect circle with a rounded edge. The final step in making the headers is charring or toasting. More on this step in a bit.

Stave blanks, on the other hand, are milled into a very complex shape. The cross-section of the final stave is a trapezoid, because the barrel inside circumference is smaller than the outside. Further, the top and bottom of the stave is narrower than the middle, because the barrel is wider in the middle than on the top and bottom.

The most crucial step in making a barrel is the barrel raising. Every barrel raiser assembles 31 to 33 wide and narrow staves into a temporary steel ring that holds the staves into place. He or she has to make sure the wide and narrow staves are distributed evenly around the circle otherwise the forces that hold the barrel together will also be uneven. In that case, the areas with less pressure are likely to leak.

If one were now to simply bend the barrel into shape, the staves would break. To make the staves pliable, the raised barrel is placed upside down with the wide end to the bottom and either placed over an open fire or hot steam is blown through the staves. A second temporary steel ring is then added giving the barrel its eventual final shape. Two more steel rings are added and the barrel now heads to the heat treatment.

The barrel's next stop is the toasting area. If the barrel is destined for a winery, the inside of the barrel is heated to a specific temperature imparting a light, medium or dark toast to the wood according the winery's exact specifications. It is this toasting process that produces the "roasted" aroma in wine.

The barrel raiser brings together 31-33 staves into a temporary steel ring (top left). The raised barrel is then heat-treated by fire or steam (lower left) to allow the staves to be bent into the barrel's final shape. Whiskey barrels are heavily charred whereas wine barrels receive a lighter toasting (top right). Once the top and bottom headers are installed, the hooper (lower center) puts the finished hoops in place. To maximize shipping space, wind barrels are shipped as kits to be assembled at their destination. Missouri's whiskey barrels need only travel to Kentucky and can be shipped fully assembled.

The toasting also enhances the presence of vanillin and creates smokey and spicey notes similar to the oil of cloves.

If the barrel is destined to hold freshly distilled "white dog" whiskey, then the inside of the barrel receives a more severe heat treatment called charring. This is done far hotter and shorter than the toasting. And while the toasting goes deep into the wood, the charring burns only the very top of the wood surface. This charcoal acts like a filter, reacting with the sharp substances of the white dog. The intense heat during the charring process creates a caramelized layer from the natural sugars present in the wood. This layer is responsible for the bourbon's amber color and caramel and butterscotch flavors. Each year of the aging process, it is the expansion of the whiskey into the wood during the hot summer months and its return back into the barrel during the cold winter months that adds more color and flavor to the spirits.

But, before that complex chemical dance can begin, the final steps in the coopering process must be done.

First, the charred barrel must be cooled down. During the cooling process the barrel shrinks. If one were to put on the finished hoops before the barrel was cool, it would shrink and the hoops would fall off resulting in a collapse of the barrel! After cooling, a groove is milled into the inside outer ends of the barrels and the prepared headers are joined with the rest of the barrel.

Finally, the heavy, temporary hoops are replaced by thin, metal hoops; pressed down by a machine called the hooper. Because wines are more acidic than spirits, galvanized hoops are used. Wine barrels are sanded smooth for appearance.

The last steps are adding the bunghole and checking for leaks. The bunghole is the entrance and exit for the wine or whiskey. It is place on the side of the barrel right in the middle of a wide stave. Right after drilling, a gallon of water is filled into the barrel and then rotated, so the water touches all the staves inside. The barrel is then pressurized. If there is a leak, one will see bubbles of water forming at the leak. If the barrel passes the pressure test, a temporary plastic bung is added and the barrel is off to the semi or to be filled. If a barrel does not pass the pressure test, it goes to the cooper station where the most experienced coopers repair the defective headers or staves.

Demand for barrels is increasing with more and more craft distilleries, wineries, and even breweries coming online every day. So, the next time you raise a glass of your favorite fermented beverage or distilled spirit, propose a toast to the Missouri white oaks!

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