A lot of the force carbonation guides that I have seen say to set the psi to 20 and leave it for 4-7 days.
Why don't we just set it to 40 (or higher) and wait 2-3.5 days?
I would assume higher pressures aren't used because of the greater possibility for overcarbonation. If you carbonate a little too long at 20 PSI your beer will be less overcarbonated than if you overcarbonated at 40 PSI. The room for error/deviation is greater at a lower PSI. Perhaps there is a more scientific answer...
For what it's worth, I usually set mine at 40psi for 24 hours, then 20psi for 24 hours, then 10psi for 24 hours, and fine tune from there. I usually serve at about 8psi.
Naturally, I pour myself a pint at each interval for quality control purposes. ;)
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2I do the same. And "quality control" is one of the perks of being a homebrewer! :) – mdma Oct 18 '14 at 13:34
