Vinegar Plant
When fluids containing sugar in solution are allowed to stand exposed to the atmosphere, their composition undergoes considerable chemical changes in a short time. The microscopic spores of various kinds of Fungi fall into them, germinate, and feed upon the sugar, which they break up into simpler combinations. Carbonic Acid gas is given off; and a quantity of Alcohol is formed at the expense of the sugar. If the fluid is allowed to stand undisturbed for some time, the Alcohol also is attacked, and is changed, by the addition of Oxygen to it, into Vinegar. These changes are accompanied by the formation, on the surface of the fluid, of a tough, slimy layer, usually covering the whole surface, but not extending to a great depth. On examining a portion of the mass, it will be found to form layer on layer, separable from one another, the lower layers hanging in a flocculent web into the fluid. The microscope shows that the mass is made up chiefly of the translucent filaments of a Fungus, consisting of short, rod-like cells, end to end, imbedded in a gelatinous substance. Some of the cells are swollen at intervals. All are very minute; but they are capable of growing and reproducing themselves, if broken off the filaments. Intermixed with these are various other forms of cells, belonging to other kinds of Fungi that grow in the fluid, since many kinds of spores usually fall into it. In fact, it is impossible to obtain an unmixed culture of such small Fungi, except by the exercise of the utmost care. Trustworthy observations and experiments prove that the production of Vinegar from Alcohol goes on only when this mass of Fungus is present (except when artificially effected by chemical agencies); hence the mass is usually known as the Vinegar Plant. Various species of Fungi have been detected in it; but there is reason to believe that the species which effects the formation of Vinegar is a member of the great group of Bacteria. It has received various names; those most commonly used are Mycoderma Aceti, Pasteur, and Bacterium Aceti, Kuetz. It forms the greater part of the Vinegar Plant, and its cells vary greatly in shape, being globular and very minute (Micrococcus), or like short rods (Bacterium form), or longer rods (Bacillus form), or filaments, as described above (Leptothrix form), all united by the gelatinous slime into what is often called a Zoogloea. Intermixed with the Mycoderma, or at times forming separate patches, are the filaments and groups of cells of Saccharomyces Mycoderma, a Fungus nearly allied to the Yeast of beer. By some botanists this has been regarded as the active agent in the production of Vinegar. Mycoderma Aceti has the power of absorbing Oxygen form the atmosphere, and of effecting its union with the Alcohol to form the Vinegar; and such cells of this Fungus as are in immediate contact with the air can even cause the breaking up of the Vinegar; into Carbonic Acid and water, by continuing the process of oxidation. In France, M. Aceti is employed in the commercial manufacture of Vinegar. Shavings of wood, covered with the Fungus, are put into solutions containing sugary substances, or Alcohol, such as beer, cider, sap of fruits, wines, brandy, &c. A temperature of from 85deg. to 95deg. Fahr. is found to give the most favourable results, both in rapidity and in amount of production of Vinegar. Mycoderma Aceti does not thrive in very acid wines or other solutions, and it generally appears in them only after they have been rendered less acid by the growth in them for some time of Saccharomyces Mycoderma. If a Vinegar Plant is allowed to remain on the fluid after it has exhausted the sugars available for its nourishment, the surface becomes covered, after a time, with blue, green, or yellow Moulds (Penicillium glaucum, &c.), or other minute Fungi. These were at one time believed to be developed as a further stage of the Vinegar plant itself; but they must be regarded as growing at the expense of the latter, when it is weakened by its food being exhausted.