Beer Forum

Some pro brewers like to button up the fermentor in the last couple of days of fermentation before sending the brew to the bright tank in order to "naturally carbonate" the brew. This saves on bulk CO2 usage, and will go part way toward hitting the desired canning/bottling carbonation level, but is it a wise move?

I imagine that at some point CO2 pressure in the fermentor might inhibit the yeast's ability to metabolize sugars, but I don't know at what point that might be reached. The pressure in the bottom of an 18 foot tall conical is already considerable. Is the additional pressure created by a 10 psi relief valve on the blowout tube going to make any real difference?

I like a nice low terminal gravity in a brew. Will buttoning up the fermentor in the last few days affect that target at all?

TIA,
Charlie

I have done this in corny kegs with lagers and using the krausening technique. I just leave the blow off valve open until it is just about done and close it up, then every 6 hours or so I would go and bleed it a little to see how high the pressure was (just by how it sounded, not with a guage). The beer finished up at 1.008, so the yeast didn't mind the little bit of pressure on them.

What vessel are you fermenting in? I would not suggest doing this in a carboy, as it might break under the pressure. Corny keg or conical seem like the only real things that can handle it.

NateBrews wrote:What vessel are you fermenting in? I would not suggest doing this in a carboy, as it might break under the pressure. Corny keg or conical seem like the only real things that can handle it.

I'm thinking about getting a conical and wondering if and/or how it will streamline the operation.

I can't imagine that the final 4-5 gravity points that yeast would consume during this "buttoning up" period would be affected as the CO2 levels put additional pressure on the yeast. They may work a bit slower (at worst case scenario), but as nate stated, they will probably still consume any remaining sugars available. Is there a formula out there for this procedure to predict potential carbonation levels?