I've brewed quite a few beers where I fermented in the kettle.
My goal, trying to keep the process simple & cleaning to a minimum, was to do the whole brewery in one vessel. At the time, I was using an induction cooktop, a 3.2gal heavy duty Italian stock pot, BIAB, & fermenting in a Craigslist found mini fridge.
What I learned:
- Aeration is still important, otherwise you risk stressing the yeast & creating off-flavors . I found aerating w/ a sanitized whisk until my arm was about to fall off did the trick.
- The beer ferments quicker, & package right when it is done. Using this method my beer was fully attenuated w/in 3-4 days. When I let it sit for anymore than 4 days, the beer started to develop off aromas & flavors that were present in the final pour. I attribute it to the fact there is no mechanisms in place to prevent oxygen ingress over longer periods of time & stop whatever makes its way in with that air.
- DON'T COLD CRASH. Thought I'd be clever & cold crash to compact the additional sediment @ the bottom. That was a dumper. When you cool liquid in a rigid, steel container, it'll suck air in to fill the space.
- The yeast was much more expressive, so its more important to control the fermentation temperature if you are looking for a cleaner ale.
- Don't use too many hops, unless you are using a hop spider or sack during the boil. The beer got a vegetal and astringent aroma/flavor when fermented on too much boiled plant matter.
The styles that turned out exceptional using this method were my English Bitters & a Belgian Tripel.
Hope this info is helpful! I'm always happy to discuss my experimental 1 vessel process if you have questions.