Sparkling wines are often made from the same grapes used in the manufacture of still wines. After the first fermentation a distinct difference in the treatment of the wines is necessitated where sparkling wine is to be made. The wine from the first fermenting cask is placed in bottles which are made of peculiar structure in order to bear the pressure to which they are to be subjected. The bottles are thick, of well-annealed glass, and the bottom is drawn into the interior of the bottle so as to form a kind of cone. This form adds great strength to the bottom of the bottle, and thus enables it to resist the pressure to which it is subjected. After the bottles are filled the cork is securely tied so that it will resist the pressure of one or more atmospheres without being blown out. The bottles thus prepared are placed in racks slightly inclined with the mouth down, and in this position they undergo the secondary fermentations, producing quantities of carbon dioxid which are dissolved in the liquid contents of the flask. During this time of fermentation there is a clarification of the wine similar to that which is produced when wine is drawn off into barrels. The solid matters which are separated from the wine consist of particles of organic matter and of tartar (acid potassium tartrate). They fall by gravitation and become aggregated in the neck of the flask, resting directly upon the inner end of the cork. In order that none of this separated material may adhere to the sides of the bottle, and thus spoil its appearance, the bottles while undergoing this secondary fermentation are shaken from time to time in order to detach any particles of solid matter and allow them to fall to the bottom. This shaking is done very skilfully by an attendant, who, at the same time, turns the bottle slightly so that the lower inclined side of it shall from time to time be a part of the whole circumference.

By the above patient and delicate manipulation the secondary fermentation is finally concluded, all of the mud, so called, is collected on the cork, and the supernatant wine is clear and bright. Usually about 18 months are necessary to produce this complete clarification.