Fermenting Tanks or Vats.— These are s•enerally made of oak, although in California redwood has been generally adopted. The capacities of fermenting tanks vary from 1.000 to 10.000 gallons.
There is a difference of opinion among wine-makers as to whether the must should be fermented in open or in closed vats. For open rats it is claimed that the fermentation is gen erally more rapid and complete, the wine is better colored, etc. Against the open vat, it is urged that the exposure to the air transforms the alcohol in the 'head' or cap, which is raised to the top by fermentation, into acetic acid and thus injures the wine. An easy way to overcome this objection is by having a false head resting on the cap, and thus keep it sub merged during the fermentation. The best practice would seem to be in having a sub merged head fermentation.
Duration of Fermentation.—This depends on a number of conditions, such as the amount of sugar in the must. the activity of the fer ments, the temperature of the vat, etc. It may be completed in two or three days, or it may run on for 15 or 20 days.
Three distinct phases of fermentation will be observed: (I) the first day or two when the ferments are multiplying; (2) the tumultuous fermentation, accompanied by a violent bubbling of the liquid and a rise in temperature, and (3) the active but relatively quiet fermentation.
As a general rule, the more rapid the fer mentation the better is the result. In the South ern States and in southern California the proc ess may be completed in one or two days. In the northern or temperate climates the time will run from seven to ten days.
The Influence of Temperature.— As we have already indicated, temperature exerts a controlling influence on fermentation. The )east works best in temperatures ranging from 59° F. to 73° F. Below 59° its action is sery feeble and slow; above 73° fermentation be comes retarded and even stops if the tempera ture passes much above 90°.
Thu>, wine-making both in very hot and in very cool climates often presents many difficul ties to be overcome. The must frequently be comes what is called •stuck•— that is, fer mentation ceases before all the sugar is trans formed into alcohol.
If the trouble comes from too low a tempera ture, the remedies are: (I) To raise the tern perature by heating part of the must; (2) to heat up the fermenting room; (3) to increase the activity of the yeast by adding sediment from vats already through fermentation, and (4) to stir up the pomace so as to bring the germs in contact with the air, as the yeast is always 'greedy for oxygen.'
When the temperature of the must in the vats rises too high, it is necessary to lower the temperature in one way or another. Se% eral methods are employed for cooling the must. Among these we may mention the use of shal low tats, racking off and refrigerating systems. The difficulties of wine-making in our Southern States and in southern California can he over come only by the adoption of a suitable system for cooling musts.
The success of the wine-maker will always depend on his success in !Ting able to control the progress of fermentation. Therefore, he should he able to control the temperature, which during fermentation has a most important in fluence (I) on the yield in alcohol, (2) on the qualities of wine, and (3) on the keeping qual ity of wines.
Drawing off the Wine.— Active fermenta tion can be recognized as being over, by the falling of the temperature, the settling down of the solid mass or mare, by the clearing of the liquid and the vinous taste and smell. The new wine will show from 0° to 2° by Balling's saccharometer, nearly all the sugar having been transformed into alcohol. It is either run into a large tub and emptied into casks or it is pumped into casks. The drawing off of the new wine leaves in the vat the "mare," which still contains a considerable quantity of material that can be made into an inferior wine.
The Different Wine Presses.— It is not necessary to enter into a detailed description of the different forms of wine presses. They work by a screw or by hydraulic pressure and they arc operated by hand, steam and electric power. Where grapes are handled on a large scale, as in some sections of France and Cali fornia, continuous presses of recent invention are used. These arc composed of two or more cylinders, worked as crushers, and after passing through these cylinders the grapes arc carried by a screw, which forces them in a perforated horizontal cylinder, terminating in an orifice through which the marc in a compact cake is ex pelled. Even the improved types of presses are not perfect as far as the yield or quantity of wine is concerned. Recent experiments show that the residue of the mare can be exhausted without presses by a process called diffusion.