Rubra, and is often employed for building and for flour-barrels and cask-staves.
The maturation of wine, whether it be in bottle or in cask, is an exceedingly interesting operation.
Later, earthenware vessels were employed, but the wooden cask -not to mention the glass bottle-was not generally known until a much later period.
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.
The wines which remain for a long period in cask gradually lose alcohol and water by evaporation, and therefore become in time extremely concentrated as regards the solid and relatively non-volatile matters contained in them.