Can you elaborate on the "tannic taste"? Tannins lend an astringent mouthfeel (fuzzy tongue and cheeks) but they have no flavor by themselves. And in my experience, astringency in beer doesn't go away unless you really, really age it, which I assume you didn't. If it's a flavor that disappeared after only a month, could it have been something else? If it was tannins, then it's just a pH issue in the mash. Keep the mash pH in the proper range (5.2ish-5.6ish). As long as it stays below 6.0, you can squeeze the bag all you want.