For any carbonated drink especially (beer, cider, kombucha, soda, G&T, rum and coke etc) it's best to chill the inside of your keg before filling. This will prevent foaming and loss of carbonation when the liquid hits warm metal.With an insulated keg it's always best to chill inside the keg before filling as otherwise you may warm your drink a bit and once it's in the keg it takes a long time in the fridge before the inside starts getting colder.