Sorry for the late reply friend... I’m not super familiar with making whiskeys but I know the mash is different, usually you’ll get your sugars from corn and grains, whereas with rums, you get them from molasses.

With whiskeys, the barrels can also differ between types, with bourbon having more of a sweet vanilla taste compared to rye.

With rum specifically, once you get into your tails, you keep what’s left behind in the pot (it’s called “the dunder”) and you pitch that into the next batch with the new ingredients. You do this about 6 times (called six generations) and after that you’ll have a significantly sweeter product.

Also not sure about pectins as I haven’t really done fruit liquors, but with standard sugar washes, you’re getting on the order of < 1000 ppm methanol if you total the whole batch, but most of that comes out in the heads. You’d have to distill about 150 liters to get a fatal amount of methanol, and no one can drink that much at once. I think throwing away fore shots is mostly for taste and less so as an actual risk aversion. Still gives most people extra peace of mind tho.