Frothing Beer

[Mike L'Itorus]

Basically the answer here is to INCREASE the line length. Pressure is too low in the lines, which means you need to increase the serving pressure to create more resistance (or REDUCE the diameter of the line) over the entire length ofthe line.

For example, 6mm line, you need around 4 meters to serve at around 75-80kpa, reduce that to 5mm and the result is less line.

As said above the LINE pressure is low, which indicates more is needed, to get a higher pressure you increase resistance, either smaller line or more of what you have.

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Wrong. Increasing resistence in the line by reducing the diameter or increasing line length will cause lower pressure at the end of the line, not higher. You contradict yourself; your second sentence states that if you reduce the line diameter, the result is less line required. This is correct. You need less line of a smaller diameter because the resistance is higher, so by reducing the diameter (and thus increasing resistance), you need less line, otherwise the pressure at the end of the line will be even lower than what you started with.

Short version;
increase resistance either by reduction of ID, or by increase of length, will lower the pressure at the tap (ie. pour pressure).
decrease resistance either by increase of ID, or by decrease of length, will increase the pressure at the tap (ie. pour pressure).

As previously mentioned, pour pressure should be manipulated by means of line length (or diameter, or both), and not by changing the pressure within the keg, as changing this pressure will change the saturation level of CO2 within the beer, ie will change the carbonation level of the beer itself (except, obviously, in instances where the keg itself has an incorrect level of carbonation ie. incorrect saturation level, and needs to be changed one way or the other).