Stocks vary widely in their resistance to attack and there is a numerical scale due to Ravaz in which 0 corresponds to zero resistance and 20 represents absolute immunity. To create a graduated scale for such an immeasurable quality is perhaps rather whimsical, and is certainly of doubtful value, but those who do use it consider that any American vine with a Ravaz figure between 16 and 20 is suitable for use as a stock.
While there is no universally satisfactory stock, there is a wide choice of resistant varieties such as Cabernet Sauvignon, Malbec, and Zinfandel; and it is quite easy to find one that is suitable for any normal soil and climate. It must also, of course, be suitable for grafting with the native vine. Amongst the more popular stocks, Colombar x Berlandieri and Chasselas x Berlandieri are used in conjunction with Palomino, and Rupestris x Berlandieri is used both with Palomino and Pedro Ximenez.
A healthy vine grown to bear fruit for eating can undoubtedly live for several hundred years. Pliny wrote of vines six hundred years old and in the patio of a school in Jerez that was formerly part of the Rivero bodegas, there is a Beba vine said to be over three hundred years old; its trunk is eighteen inches wide and it is ten feet high. The doors of Ravenna Cathedral are made of wood from a giant vine, and vines planted at Santa Barbara by the first Californian settlers grew to have a base circumference of eight feet.
In 1895 one of them yielded nine tons of fruit. There were certainly vines over a hundred years old at Sanlucar until the time of the phylloxera, and the great Black Hamburg at Hampton Court, which was planted in 1768, is still giving a full yield of fruit. In fact, if carefully tended, a vine goes on almost forever, but if the grapes are to be used for, Pinot Grigio [http://www.wineaccess.com/wine/grape/Pinot%20Grigio/Gris], or Chardonnay, a concentration of goodness and flavor is necessary that can only be obtained from vines that are relatively young.
Before the phylloxera, the useful life of vines in the sherry area varied between fifty and eighty years, and they never gave first class wine until they were twenty or twenty-five years old. The grafted vines have really productive lives of only twenty-five to thirty years, though some growers do not uproot the vines until they are as much as forty-five years old, giving a much reduced yield of top-quality must.
To offset this a little they give up to 20 percent more must and produce good wine when they are only five years old. Many of these are owned by shippers, who gain on the roundabouts what they lose on the swings, but some of the large vineyards are still controlled by landowners, who sell their produce by any of three methods:
• Compra de uvas
• A la piquera
• Al deslio
The first method, as a rule, is used by small growers, who sell their grapes as fruit delivered to the buyer’s press-house, not as grapes for Pinot Noir, Cabernet Franc, or.
In the second method, the shipper buys the must as soon as it is prepared and gambles on its quality, trusting that the grower will not water it down, though some growers deliberately add a little water to must pressed from grapes that are very overripe; he may also gamble on the quantity and buy the whole output of a vineyard early in the year, though this method is less usual.
In the third, he buys the must when it has been racked off the lees after fermentation has ceased. The more important shippers generally buy what they need by a combination of the latter two methods.