From the HBD Archive
From: hsfmsh!hsfdjs!suurb@Sun.COM (Dave Suurballe)
Subject: Priming Draft Beer
Date: 1989-07-12 22:32:36 GMT

Gregg TeHennepe writes (in #199):

> I was just planning to follow normal procedure, except to dump
> the priming sugar into the keg instead of the bottles -
> is this okay? Another potential problem is that there will be
> a significant air space in the keg, since my secondary carboy
> is only 5 gal. Is this a problem?

No, this is not a problem, but you need to use a different
quantity of priming sugar, because you have a different
liquid-to-air ratio in this container.

I'm sure you've noticed this phenomenon. When I bottle a batch,
the last bottle is never completely full, and when the beer is
completely conditioned, that last bottle is always undercarbonated.
That's because there was less beer in the bottle, and therefore
less sugar in the bottle, and therefore less gas in the bottle
after conditioning. And if there's less gas in the bottle,
there's less gas in the beer.

Kegging a batch is just like bottling a batch, except that
you're using only one big bottle instead of fifty smaller ones.
If the head space in the big package is the same as in the
small ones, you could use the same priming as when you bottle,
but it isn't. It's more like the big head space in the last
bottle of the fifty, and if you use the same priming, the keg
is going to be undercarbonated, just like the last bottle.
Obviously, the bigger the head space, the more sugar you are
going to need.

I don't know how full you normally fill your bottles, but let's
assume it's about 12 ounces of beer and 1.5 ounces of air. Your
current quantity of priming sugar is correct for this ratio only.
The keg is going to be 5 gallons of beer and 2.75 gallons of air,
and the beer has to have more sugar in it to fill the extra air
space at the correct pressure.

The formula is:

ounces of beer in bottle 7.75
keg priming = ------------------------ * ---- * bottle priming
bottle size in ounces 5

For example, assuming you prime with a cup of sugar, and you
siphon 12 ounces of beer into 13.5-ounce bottles:

12 7.75
keg priming = ---- * ---- * 1 cup = 1.38 cups
13.5 5

If your 5-gallon batches, like mine, are not always exactly
five gallons, substitute the actual size for the '5' in the
formula. In the example above, a 4.75 gallon batch in the
keg would need 1.45 cups of sugar. (I'll bet the difference
is insignificant).

The formula can apply to different keg sizes, as well.
Substitute the true keg size (in gallons) for the '7.75'.

Dave Suurballe

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