The sweet cider as it comes from the press may either be placed at once in barrels, which should not be filled more than two-thirds to three-fourths full, or if one has suitable wooden tubs or vats in a clean, cool place, it may be stored there for twelve to [Page 9] twenty-four hours to permit settling, after which it should be transferred to barrels. The bung should be left out and a loose stopper of cotton batting inserted in the hole to decrease evaporation and prevent dirt from falling in. The barrels should not be tightly stoppered until the vinegar contains at least 4.5 to 5.0 per cent. of acetic acid, at which time they should be filled entirely full and securely bunged. Throughout the entire period of vinegar making, the casks should be placed on their side and not on the end. This gives the cider a larger free surface exposed to the air, which is quite essential to rapid vinegar formation. It may be of some advantage in admitting air to bore a one and one-half inch hole in each end of the barrel along the upper edge. If this is done, the holes should be covered with fine wire gauze or two thicknesses of cheese cloth to exclude small vinegar flies. _The Alcoholic Fermentation._ A few days after the cider is put into the barrels, the characteristic frothing appears at the bung-hole. To use a common expression, "It is beginning to work." This indicates that the alcoholic fermentation, the first step in the vinegar making process, has begun, and the sugar of the apple juice is being converted into alcohol and carbon dioxide gas. The first of these substances is too well known to need any further comment other than to state that it is this element of "hard" cider that gives it its intoxicating property. With carbon dioxide, many of us are not as well acquainted. It is this gas escaping from the fermenting cider that causes the frothing and likewise the foamy appearance of the bread sponge. It is this gas dissolved in the cider or in the carbonated drinks at the soda-water fountains that imparts to them the characteristic bite or tingle, and upon escaping from the stomach produces that peculiar sensation in the head and nose. Strangely enough, this same gas is the active principle of practically all chemical fire extinguishers. Now, what is the exciting agent which starts up the fermentation in the bread sponge and in the sweet cider? In both cases it is the same: a microscopic organism, the yeast plant. In the one instance we add a yeast cake to the bread mixture; in the other we either trust to the wild yeasts of the air and the skin of the apples or following the more recent, approved method, we add a yeast cake or a pure culture of a yeast selected especially for this purpose.