This technique, used almost exclusively on red wines, allows winemakers to control the amount of oxygen that wines in tank are exposed to. The apparatus involves chambers connected by tubes and valves to an oxygen tank. Small, measured amounts of oxygen are allowed to pass through the wine via a porous stone or ceramic plate at or near the base of the tank. The benefits of this type of oxygen exposure include prevention of oxidation and reduction as well as promotion of healthy yeast cultures, which prevent stuck fermentations. Micro-oxygenation is also believed to soften tannins and, in conjunction with the use of oak chips, is frequently practiced as an alternative to oak barrel aging.