How low do you purge your BBT?

[kererubrewing]

We are using a lot of CO2 purging our BBTs to below 20 PPB of oxygen. It's my thinking that at 100 PPB off the top of the BBT it should be sufficient to have a decent blanket to the beer coming into the tank.

What are other people doing?

[Yellowbeard]

It depends on you tolerance for CO2 usage.

There's been a lot of discussion about the "blanketing" effect of incomplete purging. While CO2 is heavier than air, they do mix readily. Mixing speeds up when the CO2, which probably began cold & heavy [due to recent expansion] begins to warm up. For my part, I'm leaning towards the the arguments against a strong blanketing effect.

But it does take a lot of CO2 to repeatedly pressurize and purge down to low PPB since you're just serially diluting the existing air. Every charge of CO2 purge yields a diminishing return in decreased PPB.

Now my preferred method is to fill the BBT with water and then push it out with CO2. For the cost of one full charge of CO2 in the BBT, you get a nearly complete purge. (The only thing that would make it better would be using deoxygenated water - but you could also CO2/nitrogen sparge the purging water with your carbonation stone and test the results.) You can use CLT water, or refill your HLT via the BBT purge.

[dick murton]

You shouldn't need to gas wash beer for oxygen reduction - EVER. You are doing something wrong, or more accurately, not doing something properly. AB can get down to 10 ppb in bright tanks without gas washing, so even a small setup should be able to get less than 100 ppb pickup.

If you purge the transfer system and the receiving tank you shouldn't pick up any oxygen. Purge properly ALL transfer pipes / hoses / pumps etc. with mains water, and this will make a huge difference. Purge with deaerated water and this will improve things further. Or purge first with water, then blow out with CO2 (or nitrogen). Purging properly means that the largest diameter pipe in your system if flushed at a minimum of 1.5 metres / sec - preferably closer to 2 metres / sec until no gas bubbles are noted at the discharge. Only the do you put the beer on.

[jebzter]

We do a complete purge after a full caustic, and acid CIP, which we have to vent all the CO2. Between full CIP cycles, it is just acid, or in some cases if we are filling same day, a water rinse followed by sani, then a purge. The purges between take all of 5 minutes to get the gas coming off of the brite to be unbearable to be near, we cap and pressurize, then begin the transfer through purged pipes. We normally see 8-10ppb of DO at the tank.

[kererubrewing]

How low do you purge your BBT?

You shouldn't need to gas wash beer for oxygen reduction - EVER. You are doing something wrong, or more accurately, not doing something properly. AB can get down to 10 ppb in bright tanks without gas washing, so even a small setup should be able to get less than 100 ppb pickup.

We are not gas washing beer. The DO levels quoted in my original post are what we are measuring from the gas being purged from our empty BBT in readying it for receiving filtered beer.

[dick murton]

Sorry - my mistake. I've been looking at DO2 levels for someone - single track mind.

I would expect 100ppb in the gas to add a minimal amount to beer. I have a couple of equilibrium charts, but they don't go down anywhere near to that sort of level of oxygen.

However 100 ppb at atmospheric pressure is equivalent to = 0.0076 mm (compared to 760 mm at sea level) - so the proportion dissolving in the beer is going to be minimal once you have a flat fill.

I have picked the following out of a document produced by Orbisphere (Hach)

"The consequence is that, with any given CO2 concentration outcome desired, you will have significantly lower oxygen concentrations for sparged beer then for injected beer. For example, in injected beer the oxygen pickup from injecting one volume of 99.95% CO2 (at 0oC) into the beer when the oxygen concentration is 0.01% is 143 ppb. But a theoretical sparging of that same CO2 into the beer at atmospheric pressure would follow Henry’s Law, and your oxygen pickup would be about 7 ppb.
In real brewing situations, however, most brewers use tank overpressure to help get sparged CO2 into solution, so you would probably be picking up about 2 times the above amount, or 14 ppb. The table below shows the expected oxygen pickup given varied percentages of O2 traces (in your CO2) when measured at sea level and at 0oC."

I realise this is talking about sparge carbonation, but you can see how little is picked up during sparging with slightly impure CO2, let alone as a top pressure only.

[arrkev]

It depends on you tolerance for CO2 usage.

There's been a lot of discussion about the "blanketing" effect of incomplete purging. While CO2 is heavier than air, they do mix readily. Mixing speeds up when the CO2, which probably began cold & heavy [due to recent expansion] begins to warm up. For my part, I'm leaning towards the the arguments against a strong blanketing effect.

But it does take a lot of CO2 to repeatedly pressurize and purge down to low PPB since you're just serially diluting the existing air. Every charge of CO2 purge yields a diminishing return in decreased PPB.

Now my preferred method is to fill the BBT with water and then push it out with CO2. For the cost of one full charge of CO2 in the BBT, you get a nearly complete purge. (The only thing that would make it better would be using deoxygenated water - but you could also CO2/nitrogen sparge the purging water with your carbonation stone and test the results.) You can use CLT water, or refill your HLT via the BBT purge.

Hi everyone, I also purge with water from the CLT then push it back to the CLT with Co2, My concerns are picking up infection from the ( filtered ) mains water and passing that onto the Sanitised tank. So I always leave a bit of Sani in the tank to negate this. Do you think my concerns are unfounded or is there something else I could be doing. Thanks.

[kererubrewing]

Do you think my concerns are unfounded or is there something else I could be doing. Thanks.

I plan to sanitise under pressure after pushing the water back to the CLT. This should result in good sanitation and no oxygen.

[arrkev]

I plan to sanitise under pressure after pushing the water back to the CLT. This should result in good sanitation and no oxygen.

Of course! So obvious, : ). Thanks!

[gitchegumee]

Purge with water....

We push our clean, filtered water back to a holding tank with N2 and reuse the water. Your water should be clean, can't imagine why you would have bugs in your water! And your QA program should be confirming this with regular water testing and BBT plating. We use N2 for purge/blanket gas. Does it mix? I don't know and really don't care because our carbonation levels stay perfect for the entire packaging run. To qualify that a bit; we do full BBTs--never less--with headspace somewhere around 15%. After transfer to BBT, we finish carbonate for a few hours the next morning. Then we package the entire batch that day, keeping head pressure with N2. Works great for us. I think if you were to have a half batch sit for a few days, it might begin to decarbonate. But in general, Dalton's law is for equilibrium conditions--when you look at actual rates, I think it takes some time to hit those equilibriums. Especially when you factor dissolved gas in a liquid with relatively low surface area/volume ratio and large volume. Seems to make the whole equilibrium thing take a long time to come about.