# Keg Priming Calculator

Discussion in 'Feature Requests' started by kblankenship11, Dec 19, 2012.

1. ### kblankenship11 Member

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#1
First off I wanted to thank LarryBrewer for diligently listening to users and adding features that we have been requesting. I love the new features that come with every release!!

So here's my question. I like to prime my kegs with sugar instead of force carbing. The bottle calculator ends up with way too much sugar than I would add for carbing a keg. I have just been arbitrarily using 50% of the sugar from the bottling calculator. I find this give me a nice carb, but I'm not sure I'm as accurate to the style that the current calculator is for bottling.

I havent seen a formula for this type of thing; but I'm sure it's based on the volume of liquid your keg can hold subtracted from the volume of beer you have. Once you know the headspace you probably add less or more sugar to get the carb you are looking for.

It would also be cool to have a force carb schedule added to the current kegging calculator. For example if I have my kegerator at 37 and put the corny on 10lbs of co2 it takes x weeks to get my keg to pressure. If I'm in a rush I put it on 30 lbs it takes x days to get to my pressure. I know a lot of people have problems estimating how long it will take to carb their keg, so this would help them out.

2. ### LarryBrewer Active Member

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#2
I had a user contact us about the same thing. He wanted an equation for how long it takes for a keg to prime. I have never seen an equation for that. The simplest thing I can think of is a linear equation. Assume in 14 days it will be fully carbed, it could produce a nice little graph. However, temperature, pressure, and volume are no doubt a part of that equation. Finding the right equation is often more work than programming it.

When it comes to adding sugar to the keg, I tried that a couple times. I think it just sweetened the beer more than it saved on CO2. Maybe I added too much? I don't get why a larger volume would require less sugar to carb?

As for forced carbonation techniques, I personally don't use those. I think it is a lot of fuss, just to speed up a natural process by a couple days. I also have a friend who tried it, and he ended up with really foamy beer. This has colored my personal view of the technique. The calculator could add support for that in some manner though.

Give out some links / equations to look at, that will speed this along.

3. ### Kaiser Member

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#3
I don't think that there is any good formula for force carbing a keg out there. Especially if you want to use elevated pressure since in that case you are not dealing with a static system but need to figure out the carbonation change over time as it approaches saturation. This is going to be an exponential equation since the rate of carbonation depends on the current carbonation and head pressure. For a fairly well defined environment like a standard soda keg, this should not be all that difficult.

Kai

4. ### kblankenship11 Member

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#4
This was the original thread I used to get my methodology: http://www.homebrewtalk.com/f35/how-muc ... eg-105601/

Finding any formula is what I've had trouble with. I'm assuming there is something that can be derived from the existing bottling formula? Since the keg is essentially one big "bottle" you'd want the same ratio of headspace and sugar that would be in a bottle.

I've been confused with when people fill their headspace in the keg with co2 after priming with sugar. Is there enough o2 in solution of the beer for the yeast to properly eat the sugar you just poured in? When I rack to my keg after pouring the sugar in I don't fill with co2 because I don't do that with bottles, so why would I do it with a keg? The next morning I'll pop the release valve a touch just to make sure it's properly pressurized and let it go.

I'll keep on the lookout for a formula for this. But I guess as a general rule 1/3 to 1/2 the sugar works for people.