Grappa is made from the skins, seeds and any remaining juices left over from wine production. Once a rough drink farmers made to get them through the winter, the push toward increased quality of Italian wines and new regulations have worked to increase the quality of grappa as well.
You see, at one time grapes were crushed mercilessly to extract every bit of liquid from them for fermentation into wine. Today the grapes are crushed ever so gently. This increases the quality of the wine by decreasing the tannins and off flavors that were once extracted from pressing the seeds and stems.
So today Grappa distilleries get to work with a good qulity vinacce, the Italian word for the skins and seeds. Wineries send their vinacce to distilleries to be made into Grappa. In fact, according to Kyle Phillips, the law requires them to do so:
"The Italian government requires that the vinacce be sent to a distiller (who will ferment the white skins), in part so it can tax the alcohol produced, and in part to keep home distillers from blinding themselves: In addition to the ethanol from the sugars, vinacce contain quite a bit of methanol, from the seeds."
The stillman is grappa's winemaker. Besides keeping the grappa free of bad components, he determines the flavor profile of the product.