I thought that bubbles in the line like that meant the liquid is over carved?
If bubbles form in the line after sitting, it means that either the beer is carbonated higher than the serving pressure, or the lines are significantly warmer than the keg. Higher than serving pressure doesn't necessarily mean overcarbed though (although it often is), and has nothing to do with this case since the bubbles are entering the line from the keg, not forming in the lines after sitting.
20 ft. may be too long? I started with 5 ft. lines (too short) and now have 10 ft. lines that work. I also think your PSI is too high. I've read 10 or 11 PSI is about right for serving.
If anything, 20' is too short. The only "problem" you'd encounter with lines that are too long is a slower pour, it's not going to cause foam or other issues. And he's pouring soda, not beer, which requires higher carbonation, higher pressure, and much longer lines.
bubbles in the line is usually an indication that the liquid in the lines is warmer than the liquid in the keg. Once it warms it cant hold as much co2 and it breaks out of the solution forming bubbles. The cure is to work on keeping the lines as cold as the kegs. Since cold air sinks, there can often be as much as 10 degrees difference between the bottom and the top of the cooling chamber. A fan moving air would help some, but with the higher pressure on soda it may not help as much as it does with the same problems in beer. If you were to pour consecutive drinks, i would bet the foaming issue would be way less by the 2nd or third when the lines were cooled from the flow of the liquid.
If the bubbles were forming after sitting for a minute I might agree, but they're clearly present as the soda enters the line from the keg, and there'd have to be a huge difference in the temperature for the bubbles to form instantly like that. It also doesn't take much flow to cool the lines and see a noticeable difference, and there was zero difference seen in the line close to the keg between before the pour and directly after.
This may sounds crazy, but I'm starting to wonder if this problem has to do with the type of sugar I have been using. I've been using either raw organic cane sugar or turbinado sugar. These sugar have much more stuff in them than the regular white cane sugar.
I'm wondering if these sugars coagulates after sitting in the firdge for a while. The reason I think that is the was a bunch of black, weird crap in the keg tonight when I cleaned it out for the next batch. The black stuff was kind of clogging up the epoxy mixers.
The first 2/3 of this keg poured fine, but then I took it out and moved it briefly, and I'm thinking that made all the black junk fall to the bottom and start clogging things up. Then, I was screwed. I'll post a pic to show what this stuff looked like.
I'm thinking about running an experiment where I take white sugar and raw sugar and put them in a solution of the same concentration, stick them in the firdge and see if the raw sugar solution coagulates.
Does that sound plausible?
Yes, if sugars and other compounds in the soda crystallize and coagulate, creating a severe restriction in the diptube, it could absolutely knock CO2 out of solution and cause the foaming you're seeing. Based on the fact that it poured fine for a while, and the evidence of the black gunk forming, I'd bet that's exactly what's going on. I'd suggest subbing a small amount of the sugar you're using for corn syrup. The corn syrup should act as an interfering agent and help prevent the other sugars from crystallizing.
