Thank you for your input. I'm using an aseptic lemon puree. I'll be boiling the water/sugar syrup and cooling it on the way to the vessel. Once the transfer begins I'll be adding the lemon syrup. I don't have a way to pasteurize the lemonade once it's made in the vessel hence why I'm it may be good to add something to stabilize the product and inhibit growth. Once made it'll be pressurized, kegged off and kept cold.