Carbonation guidelines

I'm curious, I've just started getting into Kegging so am still definitely new around how to carbonate in the keg, and how to get that to actually work correctly.

Looking at say this site http://www.homebrewsupply.com/wp/wp-content/uploads/2016/02/carbonation_cart.png if I have my beer at 38 degrees, I can carbonate with 3 PSI for a Stout/Porter to achieve 1.71 carbonation level, all good. However if my beer is 1 degree warmer at 39, the minimum seems to be 5 PSI to get 1.86 carbonation level, even though in theory 4 PSI is still 1.77 carbonation level.

Can anyone explain why that is the case? I'm just curious but it's struck me as odd.

I'm not sure what your question is, the formula is not that "twitchy".
Increasing the temperature by 1°F would only require the slightest increase in CO2 pressure to maintain 1.7 volumes...

Cheers!

The question is why is 1.77 carbonation level (4PSI at 39 degrees) undercarbonated, where 1.71 carbonation level (3PSI at 38 degrees) good carbonation for a stout?

It seems like the low level range (the rollover from under carbonated to stout/porter carbonation range) has some very quirky stuff, and I'm just wondering if anyone knows why.

Ohhhh. Your issue is with the table then.
No problem, the table is FUBAR.

Clearly, if you were to fit a curve to the problem it would be a lot smoother in that region than the table indicates.

And beer is not that binary

Cheers!

Realize also that those "guidelines" are arbitrary - undercarbed/overcarbed is relative. Unless you're used to drinking a lot of cask ales 1.71 is going to seem pretty low. Most bottled commercial browns, porters, stouts are not carbed that low and I don't personally go that low unless they are going on nitro. By the same token 2.2 would likely seem undercarbed to me for a pale ale despite the fact that it's in the "proper" range for the chart. My advice is figure out what you like for a given style and go with that, or if you're planning multiple taps and don't want a bunch of secondary regulators pick something mid range like 2.4-2.6 for everything.

arla said:

The question is why is 1.77 carbonation level (4PSI at 39 degrees) undercarbonated, where 1.71 carbonation level (3PSI at 38 degrees) good carbonation for a stout?

It seems like the low level range (the rollover from under carbonated to stout/porter carbonation range) has some very quirky stuff, and I'm just wondering if anyone knows why.

Click to expand...

Don't be confused by colors. Look at volumes of CO2.

Keep it simple.

38*F, 10-12 psi, 10-12ft 3/16" beer lines. Pour the stout and let it off-gas while it sits in the glass 15 min and warms up to proper English ale drinking temp (50-52*F).