Typically the microOx application continues for one to three months, through malolactic fermentation (MLF). The stopping point is a judgment call, based upon a collective feel for when the wine has reached its optimum, and is ready to go to barrel.

Stonestreet Cabernet Sauvignon is aged in French oak barrels, and the lots that have been micro-oxygenated seem to need slightly more SO2 additions. However, according to Weerts, they integrate extremely well with the oak.

George Phelan, winemaker/general manager of Dunnewood Vineyards (Ukiah, CA), divides his rationale of the use of microOx between those wines that have problems, such as H2S, and those that need further development, particularly press and blending lots, which have structure but need a push to soften the tannins or enhance the fruit. While reds have been the primary targets, he has used it on Sauvignon Blanc to reduce a H2S problem.

Phelan incorporates microOx as soon as the wines are dry, in October or early November. Often oak chips and/ or oak inserts are added at the same time. O2 rates can go as high as 30 mL/L/month. If the microOx is still in use after MLF, and after SO2 adjustments, the O2 rates are reduced to 3 to 4 mL/L/ month.

"We use microOx on virtually any tier of wine, depending on what we are trying to accomplish," Phelan explains. "If we are trying to resolve some of the tannins, or remove some H2S, we may use microOx on any wines that will be aged in barrels after microOx. Otherwise, we use microOx and barrel staves and/or chips on California appellation wines that may not see any other wood."

With a portable Oenodev system that can be moved from tank to tank, Phelan and his crew usually only microOx 10 to 20 lots per year; however they do expect that to increase its use as they gain confidence with the equipment and it's potential.

At least three suppliers in the U.S. offer an array of equipment to meet the needs of any winery, regardless of size. This article shares the experience of ten U.S. wineries that are using microOx systems.

There are many reasons why winemakers use this process to introduce controlled amounts of oxygen into a wine - from wine enhancement, to better oak integration, faster barrel ageing, to fix problem wines - in almost all stages of the winemaking process.

In the last several years, Don Blackburn, Randall Graham, and Tom Cottrell, among others, have published excellent reports outlining the technology involved with micro-oxygenation (microOx); this report will update the techniques they described and provide current thinking about how microOx is utilized in wineries.

Graham Weerts learned about microOx in his home country (South Africa), applying it to Cabernet Sauvignon, Merlot, and Shiraz. Upon arrival as winemaker at

The 2004 vintage, with a hotter than normal growing season that stressed many shallow-soil, mountain vines, provided a perfect opportunity to apply microOx technology on individual lots. For the past two years, he has rigorously tasted the many lots and choosen a few - those with high pyrazine (bell pepper) or related compounds, a "sandy or grippy" tannin mouthfeel, or sulfides - to add oxygen.

Weerts feels that the opportune time to add oxygen is right after primary fermentation. Using a trial chart developed by Oenodev (microOx equipment supplier), he and his associates taste the wines for acetaldehyde, sulfide, and vegetal intensity, fruit expression, and tannin evolution. Then, monitoring for dissolved oxygen (DO), oxygen is slowly introduced, typically at less than 10 mL/L/month.

Daily and weekly tastes are used to scrutinize the perceptive changes in the wine, and allow the winemakers to determine the needs for additional doses of oxygen. Dissolved oxygen content is also a marker for increasing or decreasing the amount of oxygen. Weerts does not want it to go above 1ppm DO.