These methods, however, tend to result in rapid oxidation and do not produce the changes in concentration that occur due to evaporation during cask
ageing. A more discrete method of influencing the rate of such reactions may be through controlling the amounts of metal ion catalysts, which are often found in
the distillate due to the use of copper stills. Barrels also exist for the malo-lactic fermentation of wines, which incorporate a heating element within the staves that
allows precise control of the temperature of the maturing beverage.