I thought that pumpernickel flour was the same as rye flour except that it is less processed. Are they both good for making sourdough starter?
As far as I know, "Pumpernickel"-flour is just simple coarsly ground rye. At least this is, what you make Pumpernickel from.
You can use whole rye flour to start a starter*. I wouldn't use too coarsly ground grains though. Once you have the starter going, you can sour coarsly ground rye with it. Again, I wouldn't feed my main starter with it but create a levain.
If you have the coarsly ground rye bought already and don't have a mill, you don't have to bring it back to the store to have it milled again. You can just go to the nearest supermarket and buy a kg bag of organic (if you want whole) rye for 1,49€ and it would be more than twice as much as you need to create a starter and feed it for weeks.
* It works best with extraction flour with high ash content / outer parts of the grains.
for making sourdough starter.