As fabulous as wooden barrels are for aging wines, they have one tremendous drawback: expense. They are costly to buy and difficult to clean. The wood will contribute aromas and flavors to wine for only one or two aging cycles, necessitating frequent replacement for many styles of wine. Taken altogether, the expenses of using wood barrels can add dollars per bottle to the cost of producing wine.
There is a barrel material that has none of these problems– stainless steel. Stainless steel containers are cheaper to produce than wood, easier to clean, require far less maintenance, and last virtually forever. They are also completely non-reactive and non-porous, adding nothing to the flavor or mouthfeel of a wine. For all these reasons and more, stainless steel is widely used for fermentation, even for wines that will be aged in wood barrels. The problem comes after that….
Left to their own devices, wines matures in stainless steel tend to have bright fruit flavors and a crisp mouthfeel. This is a style that some prefer, especially for lighter wines, but it also lacks the depth and complexity that wine lovers have come to expect for so many kinds of wine.1 To be able to take advantage of the cost savings offered by aging in stainless steel, winemakers have had to find ways to reproduce the sensory characteristics derived from wood barrels in their production processes.
One of these techniques, called micro-oxygenation, is the controlled release of small amounts of oxygen into wine through a ceramic disk placed at the bottom of the barrel or tank. The ceramic breaks up the oxygen into microscopic bubbles that are quickly absorbed by the wine.
Originally developed in southwestern France during the early 1990s to speed the maturation of wines based on the highly tannic Tannat grape, micro-oxygenation has been adapted for a wide variety of vinifcation uses, including helping wines maturing in stainless steel to develop in a manner similar to wooden barrels. For this purpose, “small amounts” means somewhere around 1 milliliter of oxygen per liter of wine per month! A detailed discussion on micro-oxygenation can be found it Duane Alexander Blaauw’s dissertation Micro-Oxygenation in Contemporary Winemaking on the Cape Wine Academy website.
With micro-oxidation imitating the slow infusion of air through wood barrel walls, the other part of the equation is incorporating wood derived aromas, flavors, and mouthfeel enhancements into wine being aged in stainless steel. This is commonly done by putting pieces of toasted wood in with the wine.
There are several advantages to this approach. While the pieces of wood interact with the wine in much the same way as barrel staves, they are much cheaper to produce as they don’t require precise shaping or bending and don’t have to be watertight. Putting the wood into the wine means that both sides (as well as the edges) are in contact with the wine, so that 100% of the wood surface area is used (as opposed to about 40% in a barrel). Lastly, the problem of cleaning the wood is avoided because the inserts are discarded after use.
The method that most closely mimics barrel aging is mounting long planks of toasted wood inside the stainless steel container. Lower-cost options include the use of shorter boards, wood cubes or chips, wood shavings, and even wood powder or sawdust. Smaller pieces tend to contribute aromas and flavors faster than larger ones, a fact that winemakers can use to reduce the production time of wine, albeit at the expense of the advantages that come from longer aging.
When combined with micro-oxygenation, the results of the plank technique have generally been good and it is widely considered a viable alternative for producing high-quality mid-priced wines. Similarly, wood cubes and wood chips can work well in younger wines. A 2011 study2 showed little difference in consumer preference for young wines aged for 6 months in oak barrels versus 6 months in stainless with oak chips added for the last month. (In fact, the oak chip wines scored higher than the barrel aged ones, though the difference was not statistically significant.) Wood shavings and wood powders are generally considered less effective than the larger pieces of wood but do impart some wood character at a low cost and with minimal contact time.
One final method for adding wood flavors and aromas to wine is the use of wood extract. Made by soaking oak chips in high-proof alcohol, extract tends to be harsh but can provide an instant infusion of wood-like character into a wine. (A common use for extract is to fine tune the flavor of inexpensive wines after dosing with wood powder and filtering.) It’s quick and cheap, and that’s probably all that can be said for it.
The general consensus in the industry is that when wood character is desired, the aging of wine in wooden barrels yields the best wines. However, most will also agree that when used to emulate (and perhaps gently accelerate) traditional methods, the techniques discussed above are capable of producing good wines at lower cost. However, as the focus shifts from emulation at a reduced cost to imitation at the lowest possible cost, the results are predictably of lower quality.
1 For those who have been following this series, it should come as no surprise that this difference in flavors has resulted in yet another style of wine. After aging part of the wine with wood and part in stainless steel, the two are blended back together. The resulting wine can have a mixture of the bright fruit flavors coming from the stainless portion and the rich mellow notes from the wood.
2 Pérez-Magariño, S., Ortega-Heras, M., and González-Sanjosé, M.L. 2011. Wine consumption habits and consumer preferences between wines aged in barrels or with chips. Journal of the Science of Food and Agriculture 91: 943-949.