OP: the sour taste is likely the bowl coat Peterson uses. I have an unstained (nude) Pete that had the exact same sour taste as a brown stained Pete. Peterson, like many large scale manufacturers dip stain their pipes, but allegedly cap the ends to avoid interior stain. Clearly, this isn’t the case for you.
The thing about pipes is that they are always a work in progress. Sometimes you need to adjust an airway, sand a rim, bend a stem, or in this case remove errant staining....the user input will continue for as long as you use the pipe (reaming, cleaning, polishing, etc). Some times the pipe is well made but the briar needs seasoning and the only way to achieve this after the block is carved is through smoking. The point is a perfect pipes is a fallacy not a norm.
Think about how deep a stain solution gets absorbed into the wood. It penetrates quite deep. IMO, I wouldn't buy a new pipe and be expected to spend hours trying to clean the freakin' thing up. If it were my first time, I'd ask for a refund.
Ugh...if you believe this is the case go split one of your pipes. I’ll replace it if you can show deep stain penetration. Briar is as likely to deeply absorb anything as it is to burst in to flames while smoking. There’s a reason briar is used over balsa.
