But why not add "mother" or vinegar to sweet cider or put [Page 11] sweet cider into an old vinegar barrel? Here is the reason: We have seen from what has gone before that alcohol is produced from the fermentation of the sugar. We shall soon learn that the acetic acid of the vinegar is formed from this alcohol. Now, in order to obtain the maximum amount of acetic acid, it is necessary to have as much alcohol as possible in the hard cider, and this can be obtained only by the complete conversion of all the sugar into alcohol and carbon dioxide gas. The complete destruction of the sugar can be accomplished only by the uninterrupted action of the yeast, and the presence of "mother" of vinegar by producing acetic acid interferes seriously with this fermentation. The yeast cells are either killed or their useful activity is checked long before all of the sugar has been changed into alcohol. This is the condition of a very large percentage of farm vinegar—just hard cider that will not and never will make vinegar. It means just this: A small part of the sugar was made into alcohol and this alcohol was at once changed to acetic acid by the "mother" present; this acetic acid killed the yeast so that no more sugar could be changed to alcohol and no more alcohol being found, no more acetic acid could be made by the "mother." We have a weak, worthless something neither vinegar nor hard cider with considerable unfermented sugar still present and incapable of further fermentation because no yeast can develop in the weak acetic acid solution. _The Acetic Acid Fermentation._ The second step in vinegar making is the change of the alcohol of the hard cider into the acetic acid of the finished product. This is accomplished by the acetic acid germ, another microscopic plant still smaller than the yeast. In some peculiar way it is able to bring about a union between the alcohol of the hard cider and the oxygen of the air so that the alcohol is transformed into acetic acid and water. As soon as the alcoholic fermentation, described in the preceding section, is completed, draw off the clear liquid, being very careful not to disturb the sediment in the barrel. Wash out the barrel thoroughly and replace the hard cider. It is believed that removing this sediment permits the acetic acid to form somewhat more quickly, and furthermore, the sediment may undergo decomposition and impart a disagreeable flavor to the cider. Again, these dregs may harbor living bacteria which either destroy acetic acid or interfere with its formation.