Funny that this should come up.
I recently read this
http://www.experimentalbrew.com/content/no-boil-experiment and decided to give it a go. I only do one gallon batches so if it's spoiled it's not a huge deal. I also recently had a miscommunication with the guys I order consumables from and ended up with a bag of mix malts I wasn't sure what to do with.
So I did one brew using my usual method (biab with one hour boil) and another with no boil. Hops wise, I just had them in the mash so it definitely won't be as bitter as the other one. Did a major 60 min addition and threw some in for the last 15 min.
Mashed out to between 75 and 80C for ten minutes as I'd read DMS forms above 80C and wanted to give it as much heat as I could to give it every chance to kill off unwanted bugs.
I overpitched my yeast a bit, again in an attempt to make it the most viable bug in the wort so the others didn't get a chance.
I just bottled the second (no-boil) batch last night so I'll be able to compare in a couple of weeks.
Things that I've observed being different so far:
My efficiencies weren't the same which resulted in a higher OG for the no-boil beer. I think I mashed full volume (fermenter volume) on that one whereas I dunk sparged for the boiled one to get more volume in the kettle. Maybe I just payed more attention to the no-boil as I new the mash had to go just right.
The no-boil fermented out lower. Strange as the OG was higher. Perhaps to do with the overpitch and maybe there were favourable compounds left which would have been removed with a hot and cold break. Possible sign of infection? Yeast on both batches was S-33 which isn't known for a low final gravity but the no-boil got down to 1.008 and pretty much 1% stronger than the boiled batch.
No off tastes noticed going into the bottle but I didn't have a big sample.
I expect the two will be quite different beers. I'm looking forward to seeing how much process affects a beer with identical ingredients. Update in a couple of weeks.
Edit: As to the question of "why?" For me the joy of homebrew is all about reading new ideas and experimentation, hence only doing one-gallon batches, so this fits the bill perfectly.