Keg Conditioning

[Closet Fermenter]

I have a theory. The reason folks got the notion that they needed to reduce the sugar when carbing a keg comes from their experience with dispensing those first couple pours. The pressure can be a bit over your typical dispensing pressure and you might get a bit of foam. I would suggest that if a bottle had a valve on the bottom that you opened to fill your glass, (without popping the cap), you would get a similar result! You could approximate this by turning a bottle upside down over a glass and popping the cap, but I bet we all can anticipate what that would look like without having to actually try it.
So, I think folks just started adjusting the sugar downward in the keg to reduce initial pressure, but were perhaps sacrificing full carbonation, which ends up being completed after tank connection.
This is the reason I referred to pulling the prv as “popping the cap”, then connecting to dispensing pressure.

This is only my guess. Others may have a better understanding or better theory; I am open to either.

 

[McMullan]

I have measured the headspace in a normally filled 12 oz bottle and a ball lock corny keg. In both the headspace was about 6% of the beer volume. So, headspace difference does not explain why there should be a difference in priming requirement.

Brew on

But if we bulk prime a batch then fill about 40 bottles, is the combined volume of headspace left in the bottles greater than the 6% headspace left in the keg?

 

[ba-brewer]

I don't remember making a post about 1 gravity point, but I've made a lot of posts, and don't remember them all. Might do some calculations if I get bored.

It is toward the end of one the other long keg sugar threads, I will look to see if I can find it.

I appreciate the time and effort you put into the calculations so thanks. I am sure your math is correct and to many people it holds true to use the same amount of sugar for kegging as bottling. I would say anyone starting out and doing their first primed keg start with half the amount and adjust as it is easier to add more carbonation then it is to remove extra.

edit: this is the postCarbing a keg with corn sugar

 

[doug293cz]

But if we bulk prime a batch then fill about 40 bottles, is the combined volume of headspace left in the bottles greater than the 6% headspace left in the keg?

No.

But my measurement was for 5.0 gal of beer (determined by weight) in a ball lock keg. If you put more or less than 5 gal in the keg, then the headspace volume to beer volume ratio changes. However, since you have roughly the same concentration (in g/L) in the beer and headspace at serving temp, you should use the same amount of priming sugar per keg independent of the actual volume of beer in the keg (you have to "carbonate" the headspace as well as the beer.)

Brew on

 

[Closet Fermenter]

If you keg before fermentation is finished, then the continuing fermentation will add carbonation to the beer. In this case less priming sugar would be required to reach a particular level of carbonation.

This makes a lot of sense. I have never (intentionally) tried to keg before full fermentation has ceased, so I’m starting from essentially flat beer when I prime in the keg, hence I need the full dose of sugar. My current rig doesn’t permit pressurized fermentation, but I just picked up a used ½ barrel sanke that I hope to move in that direction.
All good stuff here!

 

[doug293cz]

This makes a lot of sense. I have never (intentionally) tried to keg before full fermentation has ceased, so I’m starting from essentially flat beer when I prime in the keg, hence I need the full dose of sugar. My current rig doesn’t permit pressurized fermentation, but I just picked up a used ½ barrel sanke that I hope to move in that direction.
All good stuff here!

Beer at the end of carbonation is not totally "flat" as it has a significant level of dissolved CO2. For example an ale fermented at 65°F in an airlocked fermenter (CO2 partial pressure = 14.7 psi), the carbonation level is 0.88 volumes. So to carbonate to 2.5 volumes, you prime with enough sugar to create 1.6 volumes.

If you fermented in an open fermenter (CO2 partial pressure = ~0), then the beer would be truly flat at the end of fermentation.

Brew on

 

[Bassman2003]

Awesome. This sounds like a cool "might try" on my next keg.

So, in retrospect, I boil up some water and add the correct amount of corn sugar, say 4oz to the keg. Let it cool a bit and then do my normal transfer. Hit it with some CO2 to set the lid and let it sit for a couple of weeks at room temp. Then, in the kegerator and hook up the CO2 line and chill to serving temp and let it sit for another week? Am I in the right area here?

Close. You would want to move it to the kegerator, let it sit for a week, then hook the CO2 up and serve. Now I have thrown a curve ball at you because to accomplish this, you would need the carbonation level in the keg to match the PSI setting of the tank gas right? That is where a spunding valve comes into play. When you put the keg in the kegerator, you would put a spunding valve on the gas post after a few days (after temps lower) and set it to the same PSI as the tank gas. Now when you hook the gas up for serving, the lines should be be balanced.

 

[DuncB]

But if we bulk prime a batch then fill about 40 bottles, is the combined volume of headspace left in the bottles greater than the 6% headspace left in the keg?

Don't think so as it's percentage by volume so it should scale up.
However I'd be interested in the surface to volume ratio for the two situations.
Maybe that has a part to play?

 

[doug293cz]

Don't think so as it's percentage by volume so it should scale up.
However I'd be interested in the surface to volume ratio for the two situations.
Maybe that has a part to play?

Surface area to volume ratio is only a factor in the rate of CO2 absorption when force carbonating, and is not a factor in the equilibrium state. When naturally carbonating, the CO2 is generated in the bulk of the beer, and surface area to volume ratio will affect the rate of CO2 "escaping" from the beer into the headspace.

Brew on

 

[DuncB]

Surface area to volume ratio is only a factor in the rate of CO2 absorption when force carbonating, and is not a factor in the equilibrium state. When naturally carbonating, the CO2 is generated in the bulk of the beer, and surface area to volume ratio will affect the rate of CO2 "escaping" from the beer into the headspace.

Brew on

But you did do some work on volume of headspace, spunding carbonation and cold crashing effects.

 

[McMullan]

Don't think so as it's percentage by volume so it should scale up.

Yes, if we compare a keg with a bottle, but not necessarily so if we compare a keg with 40 bottles, in terms of priming sugar needed. I don’t know, I haven’t done any measurements, but I did notice over carbonation issues when I first started using priming sugar to naturally carbonate in kegs. It might have something to do with avoiding knocking out CO2 whilst racking to a bottling bucket with enough force to swirl and mix the priming sugar solution well. Or something peculiar about bulk conditioning, where the much higher total number of yeast cells in a keg remains above a threshold for longer therefore carbonating to a higher level. That assumes some fermentable priming sugar remains in bottle conditioned beers for longer, over our brewing time frames at least.

 

[Closet Fermenter]

Close. You would want to move it to the kegerator, let it sit for a week, then hook the CO2 up and serve. Now I have thrown a curve ball at you because to accomplish this, you would need the carbonation level in the keg to match the PSI setting of the tank gas right? That is where a spunding valve comes into play. When you put the keg in the kegerator, you would put a spunding valve on the gas post after a few days (after temps lower) and set it to the same PSI as the tank gas. Now when you hook the gas up for serving, the lines should be be balanced.

No doubt that this will work. The option I prefer is to just draw a few beers to get that pressure down! Cheers!

 

[mac_1103]

It might have something to do with avoiding knocking out CO2 whilst racking to a bottling bucket with enough force to swirl and mix the priming sugar solution well.

It might. But I don't see how it can have anything to do with the amount of headspace in 40 bottles rather than 1. 6% is 6% no matter what the total number is. What am I missing?

 

[McMullan]

It might. But I don't see how it can have anything to do with the amount of headspace in 40 bottles rather than 1. 6% is 6% no matter what the total number is. What am I missing?

That 6% of a keg is not comparable to 6% of a bottle? That ideal equations might not be valid here? Clearly, things don!t seem to scale up linearly. Bottling priming calculators don’t seem to work for keg priming.

 

[doug293cz]

But you did do some work on volume of headspace, spunding carbonation and cold crashing effects.

Yes, but none of those calculations dealt with the effect of rates.

Brew on

 

[VikeMan]

I have made headspace volume measurements similar to the ones @doug293cz made, and the results agreed pretty well. The difference between keg and bottle headspace percentages (keeping in mind the fill level assumptions previously mentioned by @doug293cz in this and other threads) is negligible.

The best evidence (besides basic physics) I can give for the idea of using the same amount of priming sugar for kegging as for bottling (keeping in mind the keg fill level assumptions previously mentioned by @doug293cz) is that I have "keg primed" several times and actually measured the resulting pressure. At the end (when the pressure stopped changing), the measured pressure agreed closely with the pressures on the standard force carbonation charts for the temperature and the targeted volumes of CO2.

 

[Closet Fermenter]

I still believe, perhaps erroneously, that it’s more of a difference in the way we dispense beer from bottles vs. kegs that is the greatest difference. We depressurize a bottle before we pour it into a glass. If we fully depressurized a keg and gravity poured the keg into a scaled up 5 gallon glass in the same careful way we pour a 12 oz bottle, I am thinking that there would be little difference.
It is for this reason that I either relieve the keg pressure after it has chilled down before hooking it up to serving pressure via tank, or just dispense the first pours from the keg before hooking it up to the tank.
I could be wrong, but this seems to work for me.

 

[Climb]

One thing I have been confused on, is the beer temperature that one should use in priming calculators? I thought I had read years ago that you should use the highest temperature (diacetyl rest) that the beer has seen during fermentation as opposed to the beers current temperature (after cold crashing) when measuring the priming sugar. I get that this makes sense if you used on open fermenter with zero head pressure, but what if you are pressure fermenting? When pressure fermenting, it seems like using the current beer temperature and current head pressure is appropriate.

 

[day_trippr]

Highest temperature sans pressure, or whatever pressure you used. In the latter case use a carbonation chart to figure volumes of CO2.

 

[McMullan]

I'd say use whatever temperature the beer was last at with yeast activity going on. It's always going to be just a reasonable underestimate by the time its been racked to a bottling bucket then bottled. If we compare the procedures at 'batch' scale, kegging has less waste and probably not so much of an underestimate generally due to better transfer. There's probably a number a factors at play. Including biology, the effects of which are often greater than the sum of its parts. Frustrating, but fun.

I'm not sure that open fermentation has that much of an effect reducing dissolved CO2 levels. It's still primarily determined by temperature and yeast activity in open fermentations. I periodically knock out a lot of dissolved CO2 when recirculating fermenting wort, but it soon builds back up again due to ongoing yeast activity. Trillions of tiny CO2 bubbles evolving throughout the fermenting wort going back into solution quite quickly and determined by temperature.

 

[mac_1103]

Bottling priming calculators don’t seem to work for keg priming.

All I can say is that they always have for me.

 

[McMullan]

All I can say is that they always have for me.

You probably like beer carbonated to a higher level then, where the difference is perhaps less noticeable. The difference at lower volumes of CO2 is very noticeable. In English ales especially, which don't complement too much carbonation generally. It overwhelms the subtle character of a fine English ale.

 

[mac_1103]

Yeah, I brew a lot more Belgian than English styles, but I still don't quite get why it doesn't scale down.

 

[doug293cz]

I have made headspace volume measurements similar to the ones @doug293cz made, and the results agreed pretty well. The difference between keg and bottle headspace percentages (keeping in mind the fill level assumptions previously mentioned by @doug293cz in this and other threads) is negligible.

The best evidence (besides basic physics) I can give for the idea of using the same amount of priming sugar for kegging as for bottling (keeping in mind the keg fill level assumptions previously mentioned by @doug293cz) is that I have "keg primed" several times and actually measured the resulting pressure. At the end (when the pressure stopped changing), the measured pressure agreed closely with the pressures on the standard force carbonation charts for the temperature and the targeted volumes of CO2.

Nice to see some real experimental data.

Brew on

 

[McMullan]

Nice to see some real experimental data.

Brew on

Better to see "experimental data" peer-reviewed and confirmed, to be fair. Biology is a bit more than ideal assumptions. That's all I can say.

 

[doug293cz]

I'm not sure that open fermentation has that much of an effect reducing dissolved CO2 levels. It's still primarily determined by temperature and yeast activity in open fermentations. I periodically knock out a lot of dissolved CO2 when recirculating fermenting wort, but it soon builds back up again due to ongoing yeast activity. Trillions of tiny CO2 bubbles evolving throughout the fermenting wort going back into solution quite quickly and determined by temperature.

Equilibrium dissolved CO2 level is determined by temperature and CO2 partial pressure above the beer. Equilibrium is not reached until all yeast activity has ceased. You can't have equilibrium if CO2 is being generated in the beer.

The CO2 partial pressure in a properly airlocked fermenter is 14.7 psia. For an open fermenter CO2 partial pressure is ~0 psia. The difference in dissolved CO2 at equilibrium is usually in the range of 0.8 to 1.2 volumes, depending on temp at end of fermentation activity.

Brew on

 

[mac_1103]

I'll take preliminary, unconfirmed data over no data every day of the week. And twice on Sundays, but who does experiments on Sundays?

 

[McMullan]

Equilibrium dissolved CO2 level is determined by temperature and CO2 partial pressure above the beer. Equilibrium is not reached until all yeast activity has ceased. You can't have equilibrium if CO2 is being generated in the beer.

The CO2 partial pressure in a properly airlocked fermenter is 14.7 psia. For an open fermenter CO2 partial pressure is ~0 psia. The difference in dissolved CO2 at equilibrium is usually in the range of 0.8 to 1.2 volumes, depending on temp at end of fermentation activity.

Brew on

I was referring to dissolved CO2 during fermentation. Perhaps you’ve overlooked where the CO2 evolves from during fermentation? The trillions and trillions of tiny CO2 bubbles evolving throughout fermenting wort. Even in open fermentations there is going to be a noticeable level of dissolved CO2. Your ideal equations can’t explain everything observed. The real world isn’t that simple.

 

[doug293cz]

I was referring to dissolved CO2 during fermentation. Perhaps you’ve overlooked where the CO2 evolves from during fermentation? The trillions and trillions of tiny CO2 bubbles evolving throughout fermenting wort. Even in open fermentations there is going to be a noticeable level of dissolved CO2. Your ideal equations can’t explain everything observed. The real world isn’t that simple.

Unless you are going to carbonate by packaging with residual fermentables (unfinished fermentation) then the dissolved CO2 content during fermentation is irrelevant. The dissolved CO2 level during fermentation is also unknowable without doing sophisticated measurements, as each fermentation proceeds at its own rate, depending on a multitude of variables. Most homebrewers package after fermentation is complete. And that is the case for which I, and many others, have done calculations.

I am usually careful to specify that my calculations and statements refer to equilibrium conditions, unless I specifically state otherwise. I am well aware of how CO2 is evolved in the bulk of the beer during fermentation. And yes, I typically only deal with the "simple" problems, as problems involving dynamic processes can be incredibly complex, and the calculations usually only apply to a very specific set of circumstances, and are not generally applicable.

Brew on

 

[Closet Fermenter]

Update: The keg that was sitting around 22psi at 65° in my closet (see #18 above)

was moved into the utility storage room and is reading 14-½ psi at 45°, sitting BESIDE my cooler; not in it!
That puts me right at 2.5 volumes, which is admittedly at the top end of the range for an Irish Stout, but definitely acceptable. I used the full 5oz. (by weight) for the 5 gallon batch.

I should get a number of good pours out of this using a Tapit 2.0 before hooking up to CO2. The bonus is that at this temperature, which is what I have my cooler set at, there’s no need to lift it over into the cooler; I can just use it where it sits.
Cheers!