just confirming I understand

[DJ]

From reading if I'm gassing my keg I can leave it at pouring pressure for about 5-6 days and it wont over carbonate...

BUT

if I set to pouring pressure (70-80kpa) and shake or aggitate for a few minutes the keg, will this make it carbonate quicker but take out the risk of over carbing?

sorry if this is a stupid question but I wanna get this kegging this down first go!!

[rwh]

Nah, if you have your keg at pouring pressure, which is how it'll be most of the time, what happens is that the partial pressure of that gas in the liquid will tend to the pressure of gas in the headspace. Exactly how much CO2 will be dissolved in the beer will depend on the pressure of the gas above the liquid, as well as the solubility of the gas in the liquid (which in turn depends on temperature).

The speed at which the CO2 dissolves in the beer is proportional to the difference in partial pressures. So, the higher you have the pressure, the quicker the gas will dissolve. Also, agitation speeds up the rate at which this equilibrium is reached. So, if you have it at pouring pressure, and shake it, you'll speed up the carbonation process, but it's not possible to overshoot and overcarbonate, because the partial pressure of CO2 is tending towards the pouring pressure in this case.

I think you're thinking of the case where people both increase the pressure and shake the keg, in which case you can overshoot and overcarbonate your beer. Then there's the "Ross" method, where you shoot your beer full of high pressure CO2 (like 400kpa or something), then turn off the gas supply, and shake, and because the gas will then dissolve quickly in the beer, the pressure in the headspace falls, and you wait until it only falls back to your pouring pressure, at which time it's correctly carbonated.

Haha, I hope I haven't confused you more!

[rwh]

So yeah, to answer your actual question, if you have it at pouring pressure and shake your keg, you can't overcarbonate, but you'll probably have to shake it for like half an hour to get decent carbonation. Most instructions have you upping the pressure and shaking for like 30 seconds.

Also keep in mind that you must do all of this once the beer is cold, because solubility of gas increases with decreasing temperature.

[DJ]

ok, so the first reply TOTALLY confussed me!!!

ok, so it'll work but its alot more effort.. and obviously more time than the "Ross" method...

I guess I'm looking for a fool proof way to carb...

[drsmurto]

I guess I'm looking for a fool proof way to carb...

Oxymoron.....




Ross' method works a treat.

[Kevnlis]

Actually "fool proof" is not used correctly, the word "foolproof" creates oxymorons when used in certain statements, but itself is not one.

Asking for "foolproof instructions" as he has done does make it an oxymoron.

So in the end you were correct Doc

[drsmurto]

Mark? Who's Mark?

[rwh]

Sorry I'll see if I can summarise a bit better:

Gases always try to reach equilibrium, so:
- If there is more CO2 in the headspace than dissolved in the beer, gas will dissolve in the beer over time, increasing carbonation
- If there is more CO2 in the beer than in the headspace, gas will evaporate out of the beer, making it go flat

Things that speed up the process:
- agitation: think shaking up a beer before you open it, it makes the CO2 come out really quickly. The same thing happens in reverse in a kegging system with flat beer and high pressure CO2 gas in the headspace.
- the difference in pressure: if you suddenly reduce the gas pressure in the head space, the CO2 bubbles out quickly (this is what happens when you pour a beer). By the same logic, if you turn up the pressure on your gas bottle, the CO2 dissolves into the beer more quickly.
- temperature: cold beer will dissolve more CO2 more quickly than warm beer.

This is why the standard technique to quickly force carbonate a beer is:

1. Chill the beer.
2. Attach your gas, at a high pressure, say 200kpa.
3. Shake it up, for a short time.
4. Turn down the gas to pouring pressure*.
5. Open the release valve to reduce the pressure in the headspace to pouring pressure.
6. Pour a beer. If it's not highly carbonated enough, go to 2.

* assuming you have a check valve, otherwise disconnect the gas in disconnect before you do this step, so that you don't suck foam into your regulator.

I'm going to stop now. Really, once you have a fiddle with your system, you'll just get a feel for how it works, but I hope I've given you a fair idea of the basics. If you need more info, try here:

A Beginner's Guide to Kegging

and here:

Achieving Correct Carbonation

[lethaldog]

A keg set initially at pouring preasure will carb up but will take a week or so hence the higher preasures, i carb mine at 50 psi for 24 hours with no shaking just whack in the fridge and hook up the gas but if your keen to wait a week or 2 then go for it