I recently (6 mos ago) switched to 2.5G batches. One of the nice side effects I didn’t expect is fast carbonation time (w/ kegs). My beers regularly seemed fully carbed after just 1 week at serving pressure.
To me, 1 week is perfect. In my experience, the beer needs that much time to condition anyway.
I’ve never kegged any other size batch, so I have no comparison. That seems to explain why I always overshoot when I try to speed carb. No need to most of the time, apparently.
I speed carbed the first 2.5G batch I kegged. I over carbed it.
Same here. 10 liters, new kegger. First batch without speed carbonation went very well. 2nd batch I tried speed carbo. Was a real mess. I must have had an impact on global warming, that’s the amount of CO2 I spent trying to fix this 
From now on have some patience. It won’t do the beer no harm, that’s for sure.
Smaller batches are great, so are larger batches when you hit the mark. I just picked up a couple 2.5 gallon kegs. Man, those things are sweet! Small and compact…I think I want some more! Being a single guy, I’ve got all the time I need to brew. So the whole economies of scale argument doesn’t really apply to me so much because I love brewing, almost more than drinking. Almost…
appreciate all the new feedback as well!
some follow up questions:
so if i carb my keg at room temp, lets just say its at 15 psi
if i put the keg into the fridge to chill afterwards, will the psi of the keg change from 15?
if it does do i then look for the proper psi to adjust to for the given new temperature?
also, would also putting in the room temp co2 tank have an effect on the psi?
I have a feeling once i have a keg i might be able to answer most of these though -.-
Say your room is 72F and you want to carb to 2.4 volumes of co2. In this case, you will set you regulator to 28.4 psi and leave the keg attached to the regulator at that setting in that temp room for 10-14 days. Now it’s carbed.
Next you move it to the fridge. If you disconnect from the regulator and place it in the fridge at 39F the head pressure will drop to 10.7 psi but the amount of co2 in the beer will still be 2.4 volumes.
When you are ready to serve you will want to connect to the regulator. You don’t want to change the carbonation level so you set the regulator at 10.7 psi serving pressure.
I made all the above calculations from Beersmith mobile.
In reality 29-30 psi at room temp is fine. When placing in fridge, turn down the regulator to 10-11 psi.
One more thing, you are better off carbonating in the fridge at serving pressure. It’s less complicated. Just put it in the fridge, set the pressure to 11 psi and wait. If your impatient like me, try a half pint every few days to see how it’s coming along.
I tend to just use carb with priming sugar in the keg at room temp if I don’t have a slot open in the keezer. When I do put the keg in the keezer; I let it get cold, vent, and hook up the gas at serving pressure.
-Tony
I generally make 5 gallon batches… However, from time to time I do make smaller batches (I have some 2.5 and 3 gallon kegs). One of the things I really like about making smaller batches is I use a couple older 5 gallon corny kegs as fermenters. I brew 3-3.5 gallons, ferment in the corny keg with a short dip tube, and then can transfer from the fermenting keg to 3 gallon serving keg under pressure with no siphon, no oxygen, etc. Works really slick.
I just bought a 5 gallon keg specifically for that purpose. You can get spunding valves for the gas in disconnect and ferment under pressure using this setup as well.
What is the max pressure you can safely ferment under? It would be nice to attach a spunding valve the last few days and carbonate while finishing up fermentation.
I think it depends on the yeast strain. I’ve heard of professional breweries going as high as 2 atm (~30 PSI). I haven’t used it for pressurized ferments yet, but the valve I have maxes out at 15 PSI.
I wonder if that is 2 atm gauge pressure or actual.