A vat ahould be filled in at most twenty-four hours. for too long a period will entail a anc cession of imperfect fermentationa, the process being completed in one portion of the rnaaa before it has begun in auother.
The best authorities agree that the grapes should be picked off the bunches before pressing, as the large atems contain but little matter useful to the fermentation of the must or the preservation of the fermented liquor. Thie operation is usually performed by a three-pronged fork. On the other hand, the pippins and skins of the grapes should always be added to the must, the former containing the preserving element, the tannin, and the latter tho colouring principle. nut in making white winea from black grapes some modification will be necessary. In the first place, taking advantage of the fact that the colouring matter in the skins is dissolved only after prolonged maceration, the pressing must be done as rapidly as posaible and the skins removed. In order, however, to correct the great defect of all white wines—the difficulty with which they are pre served—the pippins should be introduced into the must either in their natural state, or the tannin may be extracted from them by boiling and the decoction added to the must.
Fermentation.—In the fermentation of grape-must, the process is arrested before its completion by withdrawing the liquor from the vat, in order that it may be subsequently continued in a less degree in the casks.
The juice which runs from the grapee during their transport to the works commencee to ferment long before it reaches the vat, in spite of all the care taken to prevent it. In the caee of highly esteemed brands of wine, this juice is fermented separately to produce the choicest varieties, but as a rulo it is added to the juice obtained by pressing, and all is fermented together. The fer mentation is conducted in vats of masonry or weed, the former being preferable, as they require less repair, maintain et more constant temperature, and are less exposed to accidents. The latter, however, when free from iron inside, are useful for small quantities. The vat must be scrupu lously cleaned before admitting the must. Stone vats are washed with warm water, and coated with milk of lime ; wooden ones are washed with warm water, and then scrubbed with brandy. These precautions are needed to ensure the destruction. of fungoid life and acid er fatty products that would injure the must.
The established conditions of fermentation are a certain degree of heat, contact with the air, and the existence of a vegeto-animal principle, aud of a saceharine principle in the must. The most suitable temperature is about 19° (66° F.); it is too slow below this point, and too rapid above it, ceasing altogether under the influence of great heat or great cold. If the tempera ture of the surrounding air does not equal at least 15° (59°F.), it must be raised to this point bv artificial means, and the must heated by mixing some boiling must with it, or better, by intro ducing, as in Burgundy, a bath cylinder. This precaution concerning the temperature is absolutely necessary, and certain results cannot be counted upon without it. The fermentation also is elower in proportion as the temperature at the time of the vintage was lower. This inconvenience also is obviated by heating the must and raising the surrounding temperature to 15° to 19° (59° to 66° F.). Experience proves that grapes gathered in the morning are slower to ferment than those plucked after noon under a het sun and in fair, clear weather. Dews, showers, and slight frosts also hinder fermentation ; hence the necessity for observing the conditions of weather before alluded to.
Air is favourable to fermentation, and is necessary to its initiation, though it may be dispensed with subsequently. It is necessary, on the other hand, that the carbonic acid liberated shall have free egress ; but this disengagement entails great loss of alcohol and of bouquet, so that it is well to cover the vat with planks, on which cloths are spread in such a manner that the contents are preserved from contact with the cold outward air, still leaving a small outlet for the generated gases. The fermentation is thus regulated ; the temperature is maintained at a higher point ; the less of alcohol and acidification of the " head " are prevented ; the aroma and bouquet are pre served ; and the fermentation is maintained under varying atmospheric conditions. The fermen tation is also more rapid and complete according as the mass is larger ; but against these advan tages, and the additional one that the wine keeps better, must be counted the facts that the larger vats require longer to fill, and that the increased heat may cause the volatilization of a portion of the bouquet.