Warning - I'm not an expert by any means.
But this is something I've wondered as well. My first few kits were fermented at room temperature (Houston, summer, marginally within the range specified by the yeast manufacturer while inside with the A/C running) and I suspect they'll have to age a good long while. Given that I've got the capacity for temperature controlled brewing now, I figured I'd try it. I don't need a fast ferment - if it takes 2 weeks for primary instead of the 1 listed in the instructions, so be it.
Throwing caution to the wind, I'm fermenting a port kit with my temp control set at 57 using premiere cuvee. I bought an extra pack of yeast at the shop when I got the kit (the kit itself came with 2, so that's 3 packs of yeast for 3 gallons
). I added 1 1/2 tsp yeast nutrient and let 'er rip. It quite happily went from 1.132 on 9/23 to 1.036 on 10/1 and 1.011 on 10/6, when I chaptalized it with the additional sugar (and another 1.5 tsp nutrient). That brought it back up to 1.026, and I'm not planning on checking it until 10/20 or so. It was still bubbling away prior to adding the sugar, so I don't think the cold temps were making the yeast sad at all.
btw, the sample at 1.036 was phenomenal. I nearly went and got another glass. At 1.011, I got some alcohol notes but still good, and even better after sugar addition. I anticipate that the f-pack added after primary fermentation will make this almost immediately drinkable.
Will I ferment kits cold again? Heck yeah. For something that clocks in under the 18% alcohol that this one should yield, I would think that the improvement would be significant.
Why wouldn't you do this? Fear of a stalled fermentation would be my #1. But adding a little extra yeast is dirt cheap, given the cost of the kit. Just do it. And throw in some nutrient, why not? And I neglected to do this - just forgot - use oxygen if you have it.
It's my understanding that tannin / color / flavor extraction from skins is reduced at lower temps. So this might be a technique best suited to whites or red kits without skins.