Kellerbier is a more generic term that means that the beer is unfiltered, served warmer than most lagers, and with less carbonation than most lagers. It originally would've been "ungespundet" or "unbunged" (German equivalent to using a soft spile and lets of the CO2 that's generated during fermentation) and served from the basement ("keller") much like British "Real Ale".
In Germany "Keller" is often a modifier that is added to another existing German beer style to indicate the afore-mentioned attributes (especially unfiltered) so you'll see "Keller Pils", "Keller Marzen", etc... If there's no modifier and it's just called "Kellerbier" than it's your basic "kellerified" Helles.
The presence of the yeast in solution means that the beer will have more perceived (and actual) bitterness vs. the lagered and filtered version as when yeast flocculate they pull IBUs out of solution as the isomerized alpha acids stick to the yeast outer cell membrane.
I'm not totally convinced that there's any large practical difference between Kellerbier than Zwickel/Zoigl but Zwickely is ALWAYS served fresh with the yeast still in suspension (it's probably served while secondary fermentation processes are still happening) and Kellerbier can be aged longer. Horst (if you can believe him) says that Zwickel has more carbonation than Kellerbier and is always served young, anyway. On his Zoigl article Horst says that Zoigl/Zwickel can be darker than kellerbier but all the Zwickel that I've had was light in color so I dispute this pretty strongly. Vienna is the place to go to find Zwickel, IMHO. Maybe Zoigl is just a darker version of Zwickel... -Never had a beer called a Zoigl, to be honest.
Personally I've actually found Zwickel to be perceively hoppier than the kellerbiers that I've had but that could be due to age. Monschof Kellerbier is a thing of beauty and it's available in flip-tops.
Landbier means essentially nothing as far as I can tell and I've had 3 or 4 of them (back-to-back); all the ones I had were made by large and low-cost German brewers and all were stored poorly, and were past their best-by date and SUPER cardboardy and nasty. -I take that back. I had ONE landbier on tap somewhere but I'd have to sift through my notes. Either way I'm not at all impressed by any of them (quite the opposite) and there seemed to be no rhyme or reason behind why a beer was called a "landbier". It seems to be a marketing term but I just can't understand the brand promise. I think it's completely unrelated to Zwickel and Kellerbier. (I'm pretty certain of this last point.) To me "Landbier means" "Crappy cardboard beer not worth your money no matter how cheap it is".
Adam
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