Pretty much all bourbon is actually sour mash. All that refers to is the use of some previously fermented mash from a previous batch (with active yeast) in each new batch, sort of like sourdough bread starter. Most bourbon distillers mention this process somewhere on their websites.
Some Tennessee Whiskeys use the "sour mash" designation on their labels simply because they can't legally use the word "Bourbon".
Nope...”Sour Mash” is a bourbon that is filtered through charoal. A process that “bourbons” do not acquire.
You have it backwards...sour mash starts out as a bourbon, then is filtered.
And you correct about the “old” mash usage...That is not the case with pure bourbon..It uses only “new” corn mash in it’s distilling processes...Then it is cased in wooden barrels for aging...Sour mash is filtered through ash charcoal before being stored in wooden barrels...