While helping out in a “Home Winemaking’ course at a local LHBS (Local Home Brewing Shop), the “foaming” occurs more often in the plastic carboys than the glass carboys (but I’m pretty sure there are other factors at play-such as temperature, pressure, amount of CO2 present (fast/moderate/slow primary fermentation), pH, amount of alcohol present, etc). If you ever drank soda or Champagne (God forbid) in a plastic cup you probably noticed CO2 bubbles clinging to the plastic cup (more so than a glass cup). I get more of a “tickle” when drinking from a glass cup than plastic cup. Just seems to me that “escaping” CO2 from an “out gassing” wine in a plastic container will "linger" longer in the "headspace" before being expelled. Soda manufactures actual look for plastic bottles that enhance this “foaming” (I guess they feel this makes their product more “appealing”).