"Dirt" Taste?

What causes a "dirt" taste in beer?

Fat Tire has it, just a little bit.

I think you're talking about the specific yeast profile. I'd use "earthy" instead of dirt, but yes I think that's what you're talking about.

I've noticed that using Safale S-33 and Danstar Nottingham dry yeasts impart an "earthy" flavor to the beers that I've used them in. It's to the point where I am considering using US-05 in everything I do except for Belgian styles. I honestly don't enjoy it at all.

I've never noticed an earthiness with nottingham.
Certain hop varieties are also described as imparting an "earthy" flavor. I think Kent Goldings has been described that way.

I know Chimay uses a hop extract instead of actual hops, but when I recently had the Chimay Red, I found that it distinctly tasted like dirt to me.

I love 'earthiness' in beers. It can come from several sources: Yeast (english strains, mainly), Hops (UK fuggles, challenger, First gold, and northdown in particular, but there are plenty of 'dank' hops out there), and malt - small additions of kilned malts like chocolate can enhance earthiness. Minerally water can also exaggerate this effect

Well, the dirt taste in mine comes mostly from all the dirt I add.

The first time I got this, I freaked out, and drank the batch as quickly as I could (good excuse, right?). It's happened again, and this time I took a more scientific approach. I noticed it in the fermenter with a high og (~1.075) wheat ale. I took a gravity reading when I noticed the off-taste, and it was still quite high. So I added some active yeast from another fermenter. I also added a bag of herbs. After a couple of weeks my gravity was down to 1.002, and the off-taste was almost gone.