The unseen influence of oak barrel aging lies not only with this ability to impart wood flavours and aromas, but also a process called elevage. This includes a multitude of biological and chemical reactions with oak, most important of which causing water and alcohol to evaporate from wine in roughly equal parts. It varies with humidity, type of oak, barrel size and can amount to 22L from a standard 225L oak barrel per year. This concentrates the remaining wine, intensifying flavours and also makes it necessary to top up the barrel periodically to prevent the ullage from oxidizing the remaining wine. Another fact is that between the costs of the oak barrel (premium French oak barrels can cost $1500+ each) and the 10% loss of volume per year; it can be a tough decision for a winemaker to use barrels.
Some wineries don’t use any barrels at all, relying on processed oak products to add wood character to their wines. There are a number of oak-alternative products which can lend toast, spice and vanilla flavours to wine, stabilize colour in reds, reduce green tannins and enhance mouth-feel. All of the oak used in alternative products is derived from the same sources as those used in traditional barrels. Selected oak trees are harvested, sawn or split and dried, either in the open air or in special kilns. They are then typically allowed to ‘season’ for several years and then the wood is then cleaned up and processed.
Processed oak comes in five main forms: powder, shavings, chips, cubes and sticks or staves. They are available with a light, medium or dark toast and you can sometimes choose between the woods of different countries and regions. They can be split into two categories, pre-fermentation and post-fermentation use.
Powder and shavings (sometimes cubes and chips) are commonly added prior to fermentation. This allows the yeast to react with and modify the tannins and aromas of the oak. The yeast actually transforms the more intense oak compounds into less aromatic ones, making the oak smoother and less aggressive. In addition, fermenting with oak encourages the formation of polysaccharides, a type of very complex sugar, which adds body to the wine and improves mouth-feel and the perception of length on the wines finish.
Staves and sticks (sometimes cubes and chips) are added post-fermentation. Instead of being transformed by yeast action, the oak aromatics and flavour compounds are simply extracted from the wood by the alcohol. Without the influence of the yeast the aroma and flavour profile is much more aggressive and more tannic, and the level of toasting shows through to a greater degree.
Described by some as the underbelly of the oak alternatives; is oak extract, the instant coffee form of the category. The trouble is that the flavour is harsh, with a ‘burnt’ nose and not a lot of fresh, toasty oak. This is how some large wineries add a touch-up of oak to their wines, by infusing a portion of the wine in with a large dose of oak powder. After the oak flavours and aromas have been extracted, they filter the oak base wine and run trials to see how much they need to blend in to the main batch to get the right character.
Cubes, sticks and staves deliver the same toasty oak character in different configurations, making them either easier or harder to handle, depending on your needs. The sticks are straight sections of oak staves, usually less than a foot long and looking like paint-stirring sticks. They can be simply plunged into a tank and allowed to soak and some of them have little holes drilled into each end, so that they can be strung together and pulled out as one piece. Staves are the same thing, and often look like barrel staves; they operate in the same way as sticks, but more slowly due to higher mass-to-surface-area ratio.
Oak cubes perform much as any other chunked or chipped oak material. However, due to their uniformity of size, they can actually be subjected to graduated toasting: i.e. they can be toasted on one side to a depth of a little less than a few millimetres, with the remaining oak cooked, but not darkened. Manufacturers claim that this configuration gives a more natural ‘barrel-like’ experience, since barrels are only toasted to a shallow depth, and wine penetrates well beyond this.
The much lower surface-to-mass ratio of these products means that they take longer to release their oak character, often over several months, used as ‘touch-up’ oak, to increase the oak profile of a wine gradually. They can be added to a tank and the wine can be checked at regular intervals to see if its achieved the right level of oak notes, then can be removed. Some like to put their oak into a muslin sack or a nylon bag in order to make it easier to retrieve and discard. Another solution is to simply wait until the fermentation has subsided, allow the oak powder or chips to settle out where they won’t affect racking.
These oak alternatives are typically packed in a hygienic manner, with no need to boil them, or soak them in a sulphite solution. Oak and other nicely-grained woods have a fascinating property of being able to maintain their hygienic character, as long as they are kept dry. The capillaries in the wood act like miniature bacterial dehydrators, killing off potential spoilage organisms. Store them cool and dry, and put them straight into the wine.
This article only scratches the surface of the role of oak alternatives in winemaking, but when you are next served a wine with an oak character for a very sharp price - you will have a little more knowledge of how it may have been achieved.