The longer tubing does not "add" any carbonation. It prevents the carbonation from escaping during the pour, leaving more in the glass. Any foam you get during pouring is carbonation escaping from the beverage. The more foam, the less carbonation in the glass.
To minimize foaming, you want the "internal" pressure of the liquid to be close to zero when it leaves the tap. The higher the pressure of the liquid at the tap exit, the more foaming you get. The beverage line has internal flow resistance that drops the pressure as you move alone the line. The longer the line, the more the pressure drop. Line is characterized by a psi/ft pressure drop, so double the line length doubles the pressure drop. The psi/ft drop depends on the internal cross sectional area of the line, which increases as the square of the internal diameter, so ID is an extremely important parameter for line length. Different line materials also have different amounts of wall friction, which affects the psi/ft rating.
3/16" ID vinyl line has a resistance rating of about 1 psi/ft (be careful there are a lot of sources, and line length calculators, on the internet that think the resistance is about 3 psi/ft. and these will give you grief.) So, your 30 psi CO2 pressure would need somewhere around 30' of 3/16" line to get low foam pours. The 4 mm ID EVA barrier line has a significantly higher flow resistance per ft than 3/16" vinyl, so you can use shorter line lengths when using this tubing.
Brew on
