Keg Conditioning

[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!

 

[doug293cz]

Update: The keg that was sitting around 22psi at 65° in my closet (see #18 above)View attachment 838114was 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!

Another data point that says keg carbing requires the same amount of priming sugar as bottle carbing.

Brew on

 

[DuncB]

Surely this data suggests that the beer has not reached equilibrium yet with the higher pressure reading. Should it not equilibrate to the same vols as before it was cooled ( given enough time ).
Unless it was still fermenting.
Also what was the target vols with the added sugar expected to be?

 

[mac_1103]

Surely this data suggests that the beer has not reached equilibrium yet with the higher pressure reading. Should it not equilibrate to the same vols as before it was cooled ( given enough time ).
Unless it was still fermenting.
Also what was the target vols with the added sugar expected to be?

22 psi at 65F is 2.1 volumes and 15 PSI @45F is 2.5 volumes. I'm not sure how precise @Closet Fermenter's temperature measurements are. But I don't think the beer should equillibrate to the same volumes since CO2 is more soluble in liquid at lower temperatures. IOW, CO2 moves from headspace to beer as temperature drops, which is why the headspace pressure drops, right?

 

[VikeMan]

IOW, CO2 moves from headspace to beer as temperature drops, which is why the headspace pressure drops, right?

There are a few interactive things going on. The solubility of CO2 in the beer increases as temperature drops, causing some net movement of CO2 from the headspace to the beer, decreasing the headspace pressure a little. And as the beer volume decreases, due to temperature decrease, the headspace increases, which also decreases the headspace pressure a little. But a big reason for the drop in headspace pressure is that gases are simply at lower pressures when they are at lower temperatures, because the gases are less energetic . (PV=nRT)

 

[Closet Fermenter]

22 psi at 65F is 2.1 volumes and 15 PSI @45F is 2.5 volumes. I'm not sure how precise @Closet Fermenter's temperature measurements are. But I don't think the beer should equillibrate to the same volumes since CO2 is more soluble in liquid at lower temperatures. IOW, CO2 moves from headspace to beer as temperature drops, which is why the headspace pressure drops, right?

The temperature measurements were not precise. In the warmer location, I left it several weeks until it stabilized. If you look at the picture in #18, you can also see the needle has passed the scale on the gauge; so again, an estimate.
After leaving it in the cooler location for awhile, the needle dropped back into the readable scale, and I used the temperature from a temperature strip on a carboy next to it; they were exposed to the same conditions and I assumed that they had reached the same equilibrium temperature. Neither precise nor accurate enough for science, but close enough for me and my brew; alas, it is beer!

 

[Bramling Cross]

Back in the olden days I used to carbonate my kegs with table sugar at kegging time. After a few days I’d pop it in the fridge overnight and tap it the following day.

I’m not one of those guys that argues that we can’t really be sure how steam beer got its name.

Oh, I know. Believe me, I know.

 

[Closet Fermenter]

I typically find my initial pressure a little higher than serving pressure, but by using a PT 2.0, I can “harvest” this extra CO2 and dispense a fair number of pours before connecting to the tank. I will admit that I may not be as particular about carbonation levels as some might be; I am ok within a range, so your preferences will determine how much you may pour before you feel the need to connect to the tank.
I will say, my tank has lasted a LOT longer after purging with fermentation gas, keg-carbing with sugar, and dispensing with the carbonation pressure.

This is my fourth pour from the naturally carbonated keg, full 5oz. corn sugar. This time, I didn’t vent the keg and hook up to gas, but just put a Tapit 2.0 on the keg and began pouring. The 15psi put it right at the top of the useable range of the tap. Admittedly, the first couple were a little foamy, but they went down the hatch just the same. With the fourth poor, the pressure dropped below 10psi, so I connected the gas line. I’m in business; not even in the cooler. Looking forward to moving up to a larger batch in my half barrel sanke!