The major difference is the base material. Most Grappa is made from a variety of grapes, whatever was left over from the winemaking processes from an equal variety of wineries. That makes for good Grappa but since it’s all mixed up you tend to get a more general flavor of grapes but no single grape, single distiller, or single distilling process.
The really exquisite, and more expensive, Grappas are almost all made from a single grape so the first thing to look out for when you’re searching for a life changer is a single grape distillate.
Nonino rocked the Grappa world back in 1973 when they released the first single grape Grappa made from the Picolit grape. That just wasn’t done at the time exactly because it was looked upon as a simple peasant drink.
Since Grappa was originally a Northern Italian spirit most of the single grape Grappas are made from grapes cultivated north of the Po River like the aforementioned Picolit, Ribolla Gialla, Moscato, and Merlot. Since then distillers have discovered that there’s gold in that there Grappa distilled from a single grape because it brings the same distinct flavors from the wine that would be made from it to the Grappa.
Larger, more industrial producers, like Nardini are generally blending a variety of grapes into a single flavor set so the scents and flavor notes tend to be less distinct. Still good, especially for a quick pick me up or a swig at the top of the slopes!