The maturation of wine, whether it be in bottle or in cask, is an exceedingly interesting operation.
The secondary fermentation proceeds slowly and the carbonic acid formed is allowed to escape by way of the bung-hole, which in order to prevent undue access of air is kept lightly covered or is fitted with a water seal, which permits gas to pass out of the cask, but prevents any return flow of air.
As a rule, the supply considerably exceeds the demand, and the stock in hand at the present time amounts to roughly four years' consumption of finished wine, but to this must be added the stock existing in cask, which is considerable.
To measure the volume of a cask, it may be assumed that the interior is approximately a portion of a spheroidal figure.
The proteid matter combines with a part of the tannin in the wine, forming an insoluble tannate, and this gradually subsides to the bottom of the cask, dragging with it the mechanically suspended matters which are the main cause of the wine's turbidity.