Oak's Balancing Act


by Jason Petros (Originally appeared in Zymurgy May/June 2008)

Oak has been used in brewing for many years, but recently it has seen a resurgence of interest due to its large flavor impact on both wine and beer. In the past, the oak flavors gained from storage in wood were considered to be a secondary benefit. Now, with the popularity of stainless steel fermenters and storage tanks, brewers and vintners alike are able to use these flavors as a creative addition to their products.

When used properly, oak can lend the most beautiful, full and rich properties of the wood and weave them delicately into the beer. When used improperly, oak can destroy the balance that you have worked so hard to achieve, and can taste like you are chewing on tree bark. A little knowledge on what oak is all about can be the difference between turning a good beer into an award-winner or lawn food.

What Exactly Happens When You Put Oak in Beer?


Oak is full of many flavorful and aromatic compounds and chemicals that, when added to beer, create another level of depth and complexity. Examples are furfural, which lends caramel sweetness, or eugenol, which is clove-like. Vanillin, the most recognizable flavor, tastes and smells like vanilla. Lipids, which constitute the oils, fats and waxes found in the wood, are responsible for oak lactones, which lend coconut and aromatic wood flavors. These are the basic flavors found in all types of oak, and the ones we as brewers are looking for. The important thing to think about when choosing oak for your beer is? How will these flavors interact with the flavors already present? Knowing which type of oak contributes which flavors is key in matching beer to wood. The three most common types of oak are American, French and Hungarian, each with its own balance of flavor and complexity. American oak has a great aromatic sweetness along with a nice vanilla component. It provides a sweet and full mouthfeel to beer, easily paired with most malt combinations. French oak also has an aromatic sweetness as well as providing a full mouthfeel, along with cinnamon and allspice characters. It is widely praised for its sweet spice and confectionary flavor compounds (custard, butterscotch, milk chocolate). Hungarian oaks are said to provide a high amount of vanillin properties, along with roasted coffee and bittersweet chocolate characters. The flavor profile of oak is enhanced during the toasting process. Which compounds come out in what ratios depends largely on the variety of oak and the level of toast it received, ranging from light and untoasted to dark and heavy. When the oak is toasted, the characteristics unique to that varietal are brought out and defined.

For example, American oak at a light toast level will lend a fresh wood and coconut character to your beers, but as toast levels increase to medium/medium-plus levels, these flavors are decreased and more vanilla and caramel notes are brought forward. Medium-plus is typically the best of all worlds in dealing with toast levels, as it brings out the qualities you would normally find in a heavier toast, without diminishing the vanilla and other softer qualities found in a lighter toast. There are many different oak delivery methods, including aging your beer in a full-size barrel, and using sawdust or barrel replica kits. Oak chips and oak cubes are the simplest for homebrewers to use. A barrel is not feasible for many homebrewers, as they require a lot of hard work tokeep them in good working order (clean, stored properly and bacteria-free). Sawdust can be hard to work with and will take some extra time to drop out in your beer, not to mention its lack of complex flavors. Staves and other barrel replica kits are geared more for use with large barrels that have lost much of their oak impact, and are often too large to be used easily in carboys. Chips and cubes, however, are very user friendly and do not need any sort of extra attention or care like their larger counterparts do.

Oak Chips and Oak Cubes


Chips are flat shreds of oak, usually about two inches long. Because there are only two sides to an oak chip, the wood reacts quickly to the heat during toasting andboth surfaces are toasted to an even level.  This gives the wood a rather one-dimensional flavor. Chips have a very short extraction time in beer, usually about a week or so, which make them ideal for use in the fermentation process. Yeast will actually metabolize certain oak compounds, like vanillin and furfural, and leave much of the spice and other characteristics behind. This creates a nice foundation to build off of with any later oak additions. Beers that do well with this method include English bitters and American pale ales-styles that generally don?t benefit from a longer aging time. Oak cubes have several layers of toast due to the thickness and shape of the cube. A toasted oak cube will have varying degrees of color along each side-these layers represent the level of heat penetration during the toasting process. Heat is what brings out all of the different and wonderful flavors of the wood, and different temperatures with different woods for different lengths of time develop different flavors. Oak cubes replicate the complex flavors of a barrel better than chips because the cubes are able to have multiple toast levels like a barrel would. Think of it as what you see is what you taste,where the different colors of the cubes provide more flavors than the single color of the chips. Cubes also have a much longer extraction time, from about two weeks up to a year depending on the size of the cube (the beer has a lot more wood to penetrate than with a chip) and the longer extraction time enables the beer to absorb the full character of the oak, and not just one or two facets of it. Cubes are ideal for beers that require a lengthy aging process such as imperial stouts and barleywines.

The Process


Many homebrewers have not experimented with oak, mainly due to one fear-sanitizing! How should I sanitize this stuff? Do I soak them in sanitizing liquid, boil them in water? Sanitizers should not be used, as the sanitizer will be absorbed by the wood and carried over into your beer.

A simple way is to steam the wood, killing anything that may be living inside. One method is to put the wood in a Pyrex measuring cup with just enough water to cover the wood. Cover the top with a saucer and heat it in the microwave until the water starts to boil. Turn the microwave off and let the wood steam for two minutes. Repeat the process twice. This should kill anything that may be living in the wood. Add the oak and the water left behind to the keg, as the water will have a nice oak essence to it. If you plan on soaking your oak in alcohol, such as whiskey, this is all the sanitizing you will need as the high percentage of alcohol will kill anything that may be living in the wood. Kegs are the best container to store your beer while it is aging on oak. You can carbonate it at the same time, and it is much easier to pull samples than from a carboy.  Once the beer has been racked into the keg, it is time to add the cubes. Eventually the cubes will end up sinking to the bottom of the keg, and because this is also where the dip tube will be pulling your samples from, you will no doubt taste a very unbalanced beer. Every three weeks or so, rock the keg gently back and forth to ensure the portion of the beer that is in contact with the oak gets properly mixed with the beer toward the top of the keg. 

If you are interested in trying your hand at a bourbon-aged oak flavor, try soaking your cubes for two weeks in a few ounces of bourbon or whiskey, and discard the whiskey before adding the oak to your beer (I find Wild Turkey blends well with darker beers). It is very easy to overdo the addition of bourbons or whiskeys, and less is definitely more which is why I prefer letting the cubes dose the beer over time. The oak should be up front, with the booze layered softly under the malt. If the flavor is not pronounced enough after two months of being on the oak, adding bourbon straight to the keg is acceptable, but be careful not to overuse it.  Tasting the beer over the next few months is a great way to see how the flavors and oak compounds blend and merge into your beer. After the first week on the oak, you will begin to taste hints of different flavors, but I find that they really start to meld after about four to six months. The longer you leave your beer in contact with the wood, the more of these great compounds will become infused with your beer. The cubes will continue to add flavor up to about a year. A great way to get that deep, complex oak characteristic is to use a one-two punch of chips in the fermenter and cubes in the keg. Adding oak chips to the fermenter will allow the beer to absorb some of those basic oak flavors we are looking for,
and gives the cubes a nice foundation to build on when they are added to the beer after fermentation. Half an ounce of chips per 5 gallons of wort is a nice place to start. You may find some beers need less, and some need more. Feel free to experiment and find a starting point that bestsuits you. The best part about oak is that it complements almost any beer!

Making beer and using oak are very similar: they are both easy to do, yet the best results require a subtle hand that is achieved only by repetition. If your first wood-aged beer does not turn out right, try again, maybe with less oak, or a different toast level-or perhaps a different varietal altogether. Maybe a blend of American chips and French cubes is the answer for your porter-who knows? Above all else, be patient. The world of oak awaits!

Jason would like to thank Shea A.J. Comfort from yeastwhisperer.com for his technical information on oak.

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