FERMENTATION. When certain vegetable substances are dissolved in water, and subjected to a due tempera ture (between 65° and 85°), they undergo a series of changes which terminate in the production of alcohol or spirit ; these changes constitute the phenomena of vinous fermentation. Sugar and some ferment are essential to the process ; and during the formation of the alcohol the sugar disappears, and carbonic acid is more or less abundantly evolved. The simplest case of fermentation is that of must, or of the expressed juice of the grape, which, when exposed, either in close or open vessels, to a temperature of about 70 , soon begins to give off car bonic acid, and to become turbid and frothy ; after a time a scum collects upon the surface, and a sediment is deposited ; the liquor, which had grown warm, gra dually cools and clears, loses its sweet taste, and is converted into wine. The chief component parts of must are water, sugar, mucilage, gluten, and tartar. During the fermentation carbonic acid escapes, the sugar disappears, and with it the greater part of the mucilage : the gluten chiefly forms the scum and a por tion of the sediment ; and the tartar, ori ginally in solution is thrown down in the form of a colored deposit. It appears, therefore, that the new products, which are alcohol and carbonic acid, are princi pally formed at the expense of the sugar ; and Gay Lussac's experiments have shown that 45 pounds of sugar are re solved, in the process of fermentation, into 23 of alcohol and 22 of carbonic acid. Sugar and water alone will not ferment ; the ingredient requisite to the commence ment of the change is the gluten, which absorbs in the first instance a little oxy gen from the air, becomes insoluble, and induces the subsequent changes. The reason why grapes never ferment till the juice is seems to depend upon the exclusion of air by the husk or mem branes; and if grapes be bruised in a perfectly close vessel, carefully excluding oxygen, the juice undergoes no change ; so that the mere breaking down of the texture of the fruit is insufficient. But a very short exposure of the pulp to air is sufficient to induce that change in the juice which leads on to fermentation, and which is afterwards independent of the further contract of air, the evolution of carbonic acid being exclusively refera ble to the decomposition of sugar. In beer the alcohol is derived from the sugar, original and produced, of the malt. When wine is exposed to air and a due temper ature, a second fermentation ensues, which is called acetone fermentation, and which terminates in the production of vinegar. During thisprocess oxygen is absorbed, and more or Iess carbonic acid in most cases evolved ; but the apparent cause of the formation of vinegar is the abstract of hydrogen from the alcohol, so as to leave the remaining elements in such proportiona as to constitute acetic acid.
Thus alcohol is theoretically constituted of charcoal, water, and hydrogen ; and acetic acid of charcoal and water only ; the oxygen of the air, therefore, con verts the hydrogen of the alcohol into water, and so effects the change into vinegar.
Essential to fermentation are : 1. Sugar, or an equivalent convertible into it. 2. Water. 3. Heat, or increase of atomic activity. 4. Leaven, or yeast. 5. Air.
Without a saccharine substance the fer mentation is acetic, or vinegar ; with it i the fermentation is vinous, or spiritu ous. These are followed by decomposi don or putrescence, called the ultimate, or putrefactive fermentation.
It is most rapid from to No vinous or beer fermentation takes place below 55° •, and above the acetone precedes the vinous while the alcohol evaporates as formed. It is slower as the heat, or atomic activity, descends towards 55°, and quicker as it advances towards 100. Again, heat should rise inversely 's quantity • 100 gallons will do best at 94°; 450 gallons at 72°, and 2000 gallons at 63°. Small vessels part with heat more rapidly than great ones ; and the time is inversely as the heat ; 100 gallons at 63° would take 8 days instead of 2. Again, fermentation generates from 2° to 22° of heat, as quantity and strength, and the sinking of this internal heat to that of the surrounding atmosphere, is the signal for the termination of the fermentation. No operation should be attempted where the atmosphere is less than 50°, and, when less, doors and vents should be closed, and fires lighted. If the atmosphere is 80° or 90°, the liquid must be set to work at 70° or SO° and smaller vessels used in summer than in winter. By regulating the heats, fermentation may be conducted with success in every season.
When fermentation is arrested, bottles or casks of hot water must be immersed, or water added to raise the When the fermentation is too rapid, it can be checked either by adding a strong solution of wort or syrup, or cooling with jets and ventilation, or by evaporation from the outside of the fermenting vessel.
Whatever diminishes the strength of the wort, or must,. increases the fermen tation; whatever increases the strength diminishes the fermentation.
Heat also increases it, and cold dimi nishes it.
No fermentation takes places in a va cuum, or in carbonic acid gas, and air is essential ; but, it is not necessary to leave the fermenting liquor uncovered, since the air penetrates and has saturated all the materials. When the fermentation has commenced, air favors the acetous more than the vinous fermentation. Much mixture with air converts the fer ment to vinegar ; and while the fermenta tion lasts, the liquor is protected by a stratum of carbonic acid gas lying over it.