Priming in a corny keg?

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Elmo Peach

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I would like to try and carbonate my beer in the keg but don't know what to do. I read somewhere to halve the priming sugar. and wait 2 weeks. any help would be great.
 
Assuming a full 5 gallons in a "5 gallon" keg, use the same amount of priming sugar as you would for bottling 5 gallons.

The old "use half" or "use two thirds" (or whatever) advice stems from someone not understanding how much headspace is actually in a corny keg vs bottles. It's essentially the same total amount.

But people believe it, because using half the priming sugar carbonates the beer about halfway (actually a little more, more like two thirds, depending on the target, because of the residual CO2 before priming) and then they put the keg on gas, which finishes the job.
 
I use brewfather to calculate amount of sugar and using option "keg (sugar)" vs "sugar" results in a difference 1:2. How accurate that suggestion is I can't say, but I haven't had any reason to complain yet.
 
I use 1/2 cup of sugar per 5 gallon keg. I let it sit for 2 weeks at room temperature, then put it in the keezer, vent it and connect it to the CO2 at 12 psi. After a few days, it it cold and is properly carbonated. I naturally carbonate in the keg to address O2 from transferring the beer to the keg and to save space in my keezer for kegs that on tap or almost ready to tap.
I tried using 1 cup per keg, but kept having over carbonation problems, so I tried 1/2 cup and that works like a charm.
 
I tried using 1 cup per keg, but kept having over carbonation problems, so I tried 1/2 cup and that works like a charm.

If you overcarbonated 5 gallons in a corny keg by using the same amount of sugar that you would have used in 5 gallons of bottled, perfectly carbonated beer, then you were putting the beer on gas before the natural carbonation was finished.

Honestly, ever time this discussion happens, I wonder how anyone can think that sugar produces twice as much CO2 in a keg as it does in bottles. It can't and it doesn't.

ETA: If you're talking about table sugar, a cup would be something like 7 ounces by weight, which would get you to about 3.5 volumes of CO2 in 5 gallons of beer, in bottles or in a corny keg. That would certainly be considered overcarbonated for almost all styles. But that would be a function of using too much sugar and not a function of the vessel in which carbonation would happen.
 
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Some more information, C&P'd from an old thread...

A standard LHBS "12 oz" bottle measured thusly...
Beer (water, with empty headspace): 12.24 fluid ounces
Headspace: 0.57 fluid ounces
(determined by weighing empty bottle, full bottle, and bottle with headspace displaced/ejected with a closed bottling wand, and doing the math)
Bottle Headspace is: 0.57 oz / (12.24 oz + 0.57 oz) = 4.4%

@doug293cz measured some kegs, and the total volume was 5.3-5.35 gallons, so a headspace of 0.3 to 0.35 gallons.
Keg Headspace is: 0.3 gallons / 5.3 gallons = 5.7% -or- 0.35 gallons / 5.35 gallons = 6.5%.

Because the headspace is actually slightly larger proportionally in a keg than in bottles, the amount of sugar to use would actually be slightly larger for kegs, but they are so close that it really makes little difference.
 
I did this a couple times in the past. But I built a spunding valve to regulate the CO2 pressure, and release it when it gets too high. It worked well, but I just hook up my CO2 tank and "set-it-and-forget-it". I just did that with a Winter warmer. I will post a picture later tonight.
 
I use the "half the amount sugar as for bottling" when keg priming beer and still usually end up with over carbed beer. Adding a spunding valve helps to keep things in check.

I don't see any difference in beer quality when priming with sugar vs using the "set and forget it" approach so I only do it when I get ahead of myself and don't have room to carb in the cooler.
 
The carbonation tool is bs3 mobile has this calculation and it is a bit lower than you would use to bottle see example screen shot.

Screenshot_20220310-215842~2.png
 
I use the "half the amount sugar as for bottling" when keg priming beer and still usually end up with over carbed beer.

Not possible, unless fermentation wasn't finished when you kegged or there was an infection. Or you hooked up the gas before all of the priming sugar was turned into alcohol and CO2. Or bottles would have also overcarbonated.

The fact that sugar is in a keg rather than in a bottle does not cause more CO2 to be produced. No way, no how.
 
Not possible, unless fermentation wasn't finished when you kegged or there was an infection. Or you hooked up the gas before all of the priming sugar was turned into alcohol and CO2. Or bottles would have also overcarbonated.

The fact that sugar is in a keg rather than in a bottle does not cause more CO2 to be produced. No way, no how.
Just telling you what I observed. No infection but can't rule out it did not started fermenting again.

The "Or you hooked up the gas before all of the priming sugar was turned into alcohol and CO2." I dont think makes senses. I used less sugar and it was not done but still got too much carbonation.

Again I am just stating what I observe and half the sugar is more than enough to carbonate beer at me house.
 
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The "Or you hooked up the gas before all of the priming sugar was turned into alcohol and CO2." I dont think makes senses. I used less sugar and it was not done but still got too much carbonation.

If you hook up gas while the priming sugar is still being processed, you end up with more carbonation than if you hadn't hooked up the gas.
 
What would you say the thinking is behind this because I see adding less mentioned in British brewing forums as well?

I think the thinking was that kegs have significantly smaller headspaces than the headspaces of all the bottles added up, so someone applied logic to an incorrect assumption, and came up a with a bad rule of thumb. And it spread like wildfire. Actual measurements, OTOH, show that the total headspaces are very close to each other, and in fact the keg headspace is even slightly proportionally larger, not smaller. But the difference isn't significant.

I'm not disputing carbonation and the amount of sugar remaining static whether bottling or kegging I'm just wondering if anybody knows why?

With headspaces proportionally the same, the amount of sugar has to be the same, because X amount of sugar can only produce Y amount of CO2 (by weight).

That said, if someone is hooking up the CO2 tank while the natural carbonation is still happening, then of course less sugar should have been used. How much less? It's anyone's guess. You'd have to know how fast the yeast are going to work vs. how fast the force cabonation is happening.

ETA: I have keg primed several beers. When I do, I put a gauge (not a spunding valve valve) on the gas post. At the end, I wind up with the pressure I'm expecting for the target volumes of CO2.
 
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I think the thinking was that kegs have significantly smaller headspaces than the headspaces of all the bottles added up, so someone applied logic to an incorrect assumption, and came up a with a bad rule of thumb. And it spread like wildfire. Actual measurements, OTOH, show that the total headspaces are very close to each other, and in fact the keg headspace is even slightly proportionally larger, not smaller. But the difference isn't significant.



With headspaces proportionally the same, the amount of sugar has to be the same, because X amount of sugar can only produce Y amount of CO2 (by weight).

That said, if someone is hooking up the CO2 tank while the natural carbonation is still happening, then of course less sugar should have been used. How much less? It's anyone's guess. You'd have to know how fast the yeast are going to work vs. how fast the force cabonation is happening.

Thanks Vikeman I've sent Brad Smith a request for a quantitative answer on this in regards to the BS carbonation tool.

They also have this on their site too which will continue to fuel the fire below:

BS: Kegging link

From the link:

Natural Carbonation

You can naturally carbonate the beer using corn sugar if you like. The recommended amount to use for priming is about 1/2 what you would normally use when bottling — approximately 1/3 cup for a 5 gallon batch. The only disadvantage of natural carbonation is that it takes some time to reach full carbonation and it can leave additional sediment in the bottom of the keg.
 
I rest my case! :)
So I sent Brad a question on the BS3 carbonation tool and he already answered.

My question to him:

Why is the corn sugar calculation significantly less than the bottling calculation from a quantitative standpoint? It seems the carbonation level wouldn't change if carbonated in the keg or in bottles with the same amount of sugar.

Thank you for looking in to this,

His Response:

I'm not certain the exact mechanism, but I believe you get more complete fermentation in the larger keg
than in a small bottle.

Cheers!

Brad Smith
 
British pub ale often is seved at a lower carbonation level. So if you want a less carbonated batch, cut the priming sugar back. Maybe that’s why they are recommending that.

4 to 4.3 oz is easy. Same level as if you were carbing up a batch of bottles. Done it dozens and dozens of times. It is a way to simplify the process.

Trub, crud, grunge and murk is left behind at the bottom. After tossing an initial half pint of glop, the rest of the keg pours crystal clear.
 
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So I sent Brad a question on the BS3 carbonation tool and he already answered.

My question to him:

Why is the corn sugar calculation significantly less than the bottling calculation from a quantitative standpoint? It seems the carbonation level wouldn't change if carbonated in the keg or in bottles with the same amount of sugar.

Thank you for looking in to this,

His Response:

I just gotta say, if the priming sugar isn't 100% fermented, there's something wrong. It's probably worth noting at this point that the standard bottle priming calculators assume 100% of the sugar is metabolized (i.e. complete fermentation), and that half of the sugar weight is turned into CO2 (and the rest turned into alcohol). Kai Troester neatly lays out the math here:
http://braukaiser.com/wiki/index.php/Accurately_Calculating_Sugar_Additions_for_CarbonationIf bottle carbonated beers were somehow leaving half the priming sugar unfermented, the bottles would consistently fail to achieve their CO2 Volumes targets.

By the logic in the response you received, beers brewed in 30 barrel fermenters would get much higher attenuation than beers brewed in 5 gallon carboys. But they don't.
 
I would like to try and carbonate my beer in the keg but don't know what to do. I read somewhere to halve the priming sugar. and wait 2 weeks. any help would be great.

after you drop your sugar and yeast you should put a few psi on the keg to keep the lid sealed. It doesn’t carb rapidly enough to seal the lid on its own.
 
If you hook up gas while the priming sugar is still being processed, you end up with more carbonation than if you hadn't hooked up the gas.
For clarity I did not put the primed kegs on CO2 while it is priming, kegs were allow to ferment out then placed into the beer cooler before putting on CO2. I do give the kegs a shot of CO2 initially to seal the lid, then draw that down to serving pressure of 12psi then no more CO2. Kegs go into the cooler and set a minimum of 2week but usually longer(I like old beer) all the while sitting on serving pressure.

I appreciate the math and have read the thread about why you should use the same amount of sugar as bottling, but even half is too much for me sometimes. It is easier to add more CO2 than to remove it so I would rather error on the side of under carbonating.
 
@ba-brewer Do you ever add more CO2 once it's at serving pressure? I'm hoping to get away from having to buy additional CO2, especially with the shortages. Thanks !
 
Since I first posted to this thread I have successfully carbonated(and over carbed too) several more kegs with half the bottling amount of priming sugar. It did/does make me wonder why it seems to work for me when it should not so I reread some threads here on HBT. I think this post explains it for me.
Carbing a keg with corn sugar

I keg in 7 to 10days, I do check that the gravity has stabilized. Even though I don't see any change in gravity before I keg the gravity is most likely still dropping slowly(or slower than my patience level). Could also be possible that the new activity from the addition of priming sugar could give a little further attenuation beyond the prime charge sort of like rousing yeast. With only about 1 gravity point needed for half the carbonation level of a typical beer almost any further attenuation of the beer will be significant.
 
Just to add here...

I think a lot of folks think of CO2 volumes as being directly proportional to the amount of priming sugar used. But in the strict sense of the term, it's not.

Half the priming sugar doesn't mean half the total carbonation. That would be ignoring the CO2 that's already in the beer before adding the priming sugar, typically ~ 0.8 volumes or so. So, roughly speaking, a beer that would have reached 2.5 volumes with "X" amount of priming sugar, would reach approx. 1.7 volumes with 1/2 of X. (In bottles or a keg, as long as the total headspace is the same. And assuming no putting the beer on gas before natural carbonation is finished, etc.)

When I carbonate in kegs with sugar (using the amount of sugar indicated by standard bottling calculators) I install a pressure gauge on the gas post, to monitor progress. When the needle finally stops moving (i.e. carbonation is finished), the pressure reading is in very close agreement with what is should be for the target volumes of CO2 at the beer's temperature. I can't think of better evidence that the process works like the science says it should.
 
I guess my real question is how long will it take to completely go flat. I would assume some time as it's in a sealed corny keg, even while serving it. I'm out of gas right now as my back up tank apparently has a burst disk in the knob and is out of commission. Which really stinks. But what better way to find out how long my cider and beer will stay carbonated
 
I'm also war gaming how to still make carbonated beer in kegs if it really gets bad and co2 in a tank becomes unavailable, because I detest bottling with a passion, lol
 
I guess my real question is how long will it take to completely go flat. I would assume some time as it's in a sealed corny keg, even while serving it. I'm out of gas right now as my back up tank apparently has a burst disk in the knob and is out of commission. Which really stinks. But what better way to find out how long my cider and beer will stay carbonated

i've used empty kegs with presure to push full ones before.....
 
i've used empty kegs with presure to push full ones before.....
were you able to pour the whole keg? I would guess no, I will be messing with kegs and forget to hook gas back up from time to time and my wife will ask if the keg is suppose to pour at a trickle. The head space pressure seems to be enough to push a beer or two but I guess that might depend on how full the keg is.
 
i've used empty kegs with presure to push full ones before.....
So this is a scenario of where you would capture the excess gas when it's in the conditioning phase.

I will let you know how it goes. My cider was a bit over carbed and it's still serving very fast. Only time will tell
 
were you able to pour the whole keg? I would guess no, I will be messing with kegs and forget to hook gas back up from time to time and my wife will ask if the keg is suppose to pour at a trickle. The head space pressure seems to be enough to push a beer or two but I guess that might depend on how full the keg is.


well i usually have 6 kegs hooked up, so it'd be more then one empty keg with co2 still in it..i just remember it got me by for a couple days...
 
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