For those of you that were at the May meeting, Angela Steil came and talked with us about draft system cleaning and balance. Very informative. She later emailed me about an important point she forgot to mention about draft system balance. Here is what she had to say…
I wanted to clear up an error I made yesterday. Amidst the fantastic questions I was receiving, I forgot to add a very important part to our system balance conversation for those of you putting together your own draft system at home. Though we spoke about Dynamic Resistance, which is the resistance we build into our system using varying tubing types, ID’s, and lengths, I forgot to mention the oh-so-necessary and important Static Resistance.
Allow me to backtrack first and take a look at the necessary Applied Pressure, which is what we need to find out first so it can balance with our total resistance. You can figure out how much applied pressure is needed if you know what temperature your cooler is going to be at and how many volumes of Co2 your beer will have in it. This is where our first chart, the Determination of CO2 Equilibrium Pressure Given Volumes of CO2 and Temperature comes into play. This is the second chart on the handout I presented, and it is not readily available as a chart online, so I had to take a picture of my physical copy to use for your handouts. I have given Jeremy here a copy to attach to an email, otherwise I recommend viewing an online version of the BA’s Draft Beer Quality Manual and it should be on page 38 of the manual.
Once your Applied Pressure has been determined, we can now look to balance the Applied Pressure with our Total Resistance, which consists of Static and Dynamic Resistance. Static Resistance, the part I accidentally skipped yesterday, is all about hydrostatic pressure, or the effect of gravity. Look at your draft system and determine, is the beer traveling upwards to the draft tower, is it traveling downwards to the tower, or is the beer in the keg perfectly level to the draft tower? We ask this because for every increased foot in elevation from the middle of the keg to the faucet on the draft tower, we need to add .5 lbs of resistance to our equation. For every decrease in elevation, we take away .5lbs of resistance from our equation. If the keg and draft tower are level, no Static Resistance measurement is necessary. So for example, if the beer in my system has to travel 5ft up from the middle of my keg of beer to the faucet on my draft tower, I therefore have 2.5lbs of Static Resistance that is built into my draft system.
Let’s take that same example of 2.5 lbs of Static Resistance and finish out our system balance equation. If we took a look at our Determination of CO2 Equilibrium Pressure Given Volumes of CO2 and Temperature chart that I listed above and from it determined that your 38F beer at 2.5 volumes of CO2 (just for example) would give you an Applied Pressure of 11.3 lbs, we would then know that our total Static and Dynamic Resistance would need to equal the Applied Pressure number (When encountering a number like 11.3, just round up to 12lbs).
So we have 12lbs of Applied Pressure that we need to equal out with 12lbs of Resistance. So far we know we have 2.5lbs of Static Resistance in our system, so we have 9.5lbs of Dynamic Resistance we need to build into the system to balance it properly. This is where our Beer Tubing Restriction Values chart comes in handy. We use the tubing types, ID’s, and lengths to put together the last 9.5 lbs of resistance that is needed to ensure our system is balanced, and that our beer is flowing properly.
Lastly, I’ll recommend you check out this Forced Carbonation Table to help you determine the psi and temperature settings needed to force carbonate your home-brew. The only sad part about this chart is that it doesn’t tell you how long the beer should be in contact with the carbonation settings, but it’s a start.
If you have any questions, please don’t hesitate to reach out! I want to thank you all for your time yesterday, and I look forward to geeking out with you again in the future.