Force Carbonation

[JC]

Hi,

Looking for some advice on force carbonating. It seems there are a few ways of doing it. And this is my understanding, can someone correct me if I'm wrong or missing something:

 1) figuring out wetting pressure (3 psi) + 11 psi for volumes wanted using chart (EXAMPLE)

2) quick connect CO2 line to carb stone

3) set regulator to 14.5PSI

Now what? Do I just wait until pressure gauge on CIP arm matches my regulator and that would generally mean you have reached an equilibrium and your cider is done? Or do I just do it for a few hours and then check it with the Z&N? Repeat? Would the results be immediate or should you wait 12 or 24 hours before checking with your Z&N?

I think I'm missing an important piece of head pressure vs pressure I put through carb stone. 

[Kirk Evans]

I'm going to assume your tanks max pressure is 15PSI and you have a PRV on it.

In my experience in that situation, I'd put 10PSI on the head of the tank and run 15PSI through the carbstone for an amount of time; maybe start with 10 minutes (really depends on size of tank, temp and headspace).

Monitor your head pressure making sure it doesn't go above 15PSI. You can check with the Zahm immediately after. Once you get a reading, you can deduce how much longer you need to run the C02.

I generally wait 24 hrs and re-check with Zahm but it should stay where it was at (meaning it's in solution), so there's not really a need to do that.

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[Alex Kroh]

Hi Jen,

I've thought a lot about this, probably too much, so please excuse the long-winded explanation. There are a few ways to go about it.

What you've suggested is basically correct but the only problem with just opening the valve after setting the target pressure like you've suggested is that the regulator will be BLASTING co2 into the tank at high pressure/flow rate so most of that gas will rise through the cider straight to the headspace. In effect, you will charge the headspace with co2 first, and then co2 will eventually dissolve back into the cider. What this means is that early on your tank gauge isn't reflective of the cider because the whole tank hasn't reached equilibrium. If you wait long enough (24-48 hrs or so) then it will achieve equilibrium and it will be basically accurate. Either way, this is what the Zahm is for - measure the cider directly. Take a few readings along the way until it stops changing, then you're at equilibrium. Some folks like to charge the headspace through the CIP arm first to about 1-2 psi below the target pressure. This can help the co2 dissolve more quickly into the cider. Still not great though if your stone is blasting co2 at high pressure and flow rate. In sum, this method works fine if you've got the time.

A better way to do it: Once you know your target pressure (based on the Zahm chart) then set your regulator to that psi (plus stone wetting pressure, 1-3psi, plus static liquid pressure - 1psi for every 28in of liquid above the stone). For example, if my cider is at 38 degrees, and my chart tells me I need 10psi to get desired volumes of co2, I set the regulator to 13psi). If you have a rotameter (measures flow rate) you can set the co2 to flow at 5-10 SCFH. At this low flow rate, the stone produces a gentle curtain of bubbles, which helps the co2 dissolve more efficiently into the cider due to the increased gas-to-liquid surface area of many fine bubbles. If you don't have a rotameter, a good way to approximate this low flow is to just barely crack the output valve of your regulator until you see the needle drop 5 psi or so - this restricts the flow, but the needle movement tells you the co2 has started flowing. Then you essentially just set it and forget it. The tank will slowly come up to equilbrium and stop carbonating at the target you've set. No need to worry about blowing the PRV or overcarbonating. This is my preferred way as we often flip our brite tanks daily and carbonate overnight and come back the next day, confirm with Zahm and you're ready to go. A little trial and error, plus some minor adjustments the next day can make this process very reliable if you have predictable cider temps.

Option two is set the regulator to something like 4 psi first and wait for the tank to come up to that pressure. Then turn the regulator up by 2psi increments and wait for equilibrium each time. Because of the small differential between regulator and tank, the co2 flows slowly, and the stone produces the fine curtain of bubbles. A little more babysitting, but largely passive. This works well if you're around to make the adjustments, you'll never overshoot.

Hope that helps.

Alex