5. The juice of the grape has acquired an agreeable flavor; has become sweet, thick, and glutinous.
6. The seeds have become void of glutinous substances.
These are the signs given by several French authors, and are here taken from Prof. Du Breuil, who says, nevertheless, that, under some circumstances the grapes should be gathered before arriving at the state of maturity indicated by these signs, and under other conditions should be gathered even later. He says:
Gathering before Complete Maturity.—1. In certain localities north of the viticultural region the grape hardly ever arrives at the degree of maturity just indicated. Yet the crop must be gathered, or otherwise it would rot on the vines. Under these circumstances, the only thing that can be done is to leave the grapes on the vine as long as they derive any benefit from it.
2. Grapes intended to make sparkling wine should also be gathered before the moment of absolute maturity.
3. In the southern part of France, white grapes intended for the making of dry wines, ought to be picked before reaching the last degree of maturity. Otherwise, in that hot climate, the quantity of sugar in the grape would increase to such an extent that it would be impossible to make a dry wine. This is the practice in making the dry white wines of Lunel, of Coudrieux, of the Hermitage, and of Saint Peray.
4. For all the ordinary red wines of the region inhabited by the olive, if the gathering of the grapes is delayed till the last degree of ripeness, the must will contain more sugar than can be transformed into alcohol by fermentation. The result will be that these wines will undergo a sort of continuous fermentation, which will make its appearance whenever they are moved, and which will soon change into acetic fermentation. The only way to cure this tendency and to render the wines capable of shipment, is to strongly fortify them by the addition of spirits. To prevent this difficulty in the first place, the grapes should be gathered before complete maturity.
Some very respectable authors, whose experience has been confined to the colder wine making regions, tell us that in all cases the grapes should be allowed to remain on the vine as long as they gain in sugar, and that in order to correct the excess that they would thus in many cases acquire, they recommend that the must be reduced by water. (See [Watering Musts].)
Gathering after Complete Maturity.—To make sweet wines, the grapes should remain on the vine until they have developed the greatest possible quantity of sugar. For this purpose the grapes are not only allowed to shrivel before gathering, but also artificial means are resorted to, such as twisting the stem, or drying them on straw after picking, and even applying heat to them in various ways. (See [Sweet Wines].)
Ripeness according to Required Strength.—If the wine maker will first determine how strong in alcohol he wishes his wines to be, he may anticipate the result approximately by testing from time to time the amount of sugar contained in the grapes, and by gathering them at the period when the sugar in the juice shows that, fermented, it will produce the desired percentage of spirit. This testing is easily performed by the use of the must-scale or the saccharometer; and for information on this subject, the reader is referred to the chapter on musts.