"If a bottle of light wine is opened, and some of the wine is left for two or three days in the partly empty bottle, the oxygen of the air acts upon the acetic ferment, and the wine becomes sour. When wine is cellared in a cask evaporation constantly takes place through the pores of the wood, and air enters by the same passages into the cask to fill the vacuum produced by the evaporation. Unless this air is frequently expelled by the addition of fresh wine all the wine in the cask is liable to turn sour. In places where draught wine is used, and where air must be permitted to enter into a cask, in proportion as wine is drawn from the tap the same difficulty occurs, and if the wine is consumed slowly, the oxygen and the acetic ferments frequently turn it into acetic acid. This is prevented by keeping within the casks a constant pressure of carbonic acid gas, which gas keeps the acetic ferment out of the reach of free oxygen, without which element the acetifica-tion cannot occur; fur the conversion of alcohol into acetic acid demands a large supply of free oxygen."