
Grappa is an Italian spirit distilled from pomace — the grape skins and seeds left after winemaking — not from wine itself. That gives it a raw, grassy grape-skin bite.
Pomace is the raw material, and that is what makes it what it is — nothing distilled from wine itself tastes the same. Aged versions trade the raw edge for oak, which is a different drink rather than a softer one.
Brandy is distilled from wine rather than pomace, and more often aged. It is rounder and softer: where grappa cuts and keeps the drink dry, brandy smooths it and adds a woody sweetness.
Pisco is made in Peru and Chile under its own appellation rules, and comes out more aromatic and softer; in place of grappa it takes a drink towards fresh grape and away from the rustic edge.
"grappa is just moonshine"
Grappa is a legally protected pomace brandy, not a rough homemade spirit. Georgian chacha belongs to the same category — also a pomace brandy — just more often made at home.
Grappa is a pomace distillate and its character is aroma, so it has a great deal to lose. An opened bottle fades noticeably over a year and faster once it is mostly air. Store it upright in the dark, and decant the last third instead of leaving it to breathe.