My last two batches, tasted both during fermentation and after fermentation completed, were totally undrinkable. I had to even spit out the tasting samples, they were so nasty. They tasted like cooked, rotting corn chowder. So my intial thought was that somehow, despite extremely rigorous sanitation (both heat AND Star San sanitization of everything that the wort touched post-boil), the batches had become contaminated with a coliform infection, which does produce massive amounts of DMS. Both batches were all-grain Bohemian Pilsners, pitched with a starter using 4 Activator Packs of Wyeast Urquell Lager. So, not knowing where the infection could have possibly come from, I decided to brew an extract batch and to vary some aspects of the process. For instance, instead of using my whirlpool tank and immersion chiller, I used a plate chiller and whilrpooled in the boil kettle, to reduce the wort's exposure to outside equipment.

So this time I tasted the wort before even pitching the yeast. It already had this disgusting, strong corn-like character. In other words the wort has exactly the same off-flavor as the previous two batches (which used completely different ingredients, being all-grain). Now I know that the taste of wort doesn't mean anything, since it completely changes during fermentation; but now that it has finished fermenting, it still has the same character. So clearly the off-flavor was not due to biological contamination, since it was there immediately after cooling.

And I can't believe that this flavor is DMS. In the previous two batches, I boiled for 90 minutes with 15 - 17% evaporation per hour and cooled to 48 degrees F within 40 minutes. For the current batch, which was extract-based, I boiled for 60 minutes with 15% evaporation and cooled to 46 F in 45 minutes. The boil was NOT covered, of course. In all three batches I whirlpooled and left a large trub cake in the kettle or whirlpool tank. Yet, the wort was still extremely cloudy.

What the heck could be going on here? How is it possible to mess a beer up so completely before you even pitch the yeast? And how can three batches end up the same using such different ingredients (two all-grain vs. one extract)? And what in the world am I tasting if not DMS? If it is DMS, how could it possibly be so strong when I have done everything that you are supposed to do to minimize it.

Even if you have an off-the-wall guess, I would appreciate the input, because I am completely stumped. My best guess at this point is that somehow I am getting trub throughly mixed in with the wort, in such a way that it is not settling out, and that this is what is giving the beer such a horrendous flavor. But that doesn't make sense to me because, in a previous batch (an Imperial Stout) I intentionally pitched the entire contents of the BK (i.e. all the trub included) into the fermenter and it turned out fine (though it had a limited shelf life).