Tall gin and tonic on ice with lime against a black background
Don't Open Room-Temperature Tonic, Especially For Gin And Tonics
By Haldan Kirsch
If you use room-temperature tonic water for your gin and tonic, your drink will lack the effervescent lift that comes from cold tonic water.
Tonic water's bubbles come from the carbon dioxide it's been infused with, and the gas dissipates faster when served at room temperature or warmer.
Since warmer temperature makes it easier for the bubbles to escape, your drink will go from bubbly to flat much faster than it would if your tonic water were cool.
Gin and tonics are stirred to bring all the components together, but over-stirring them will release more of the trapped carbon dioxide gasses, resulting in a flatter drink.
So, unlike some other cocktails, a gin and tonic can't rely on vigorous stirring to let the ice cool down the drink, which is another reason to use cool tonic water.
If you don’t have cold tonic water, cool it quickly by wrapping the tonic bottle in a damp washcloth before putting it in the freezer — or chill the cocktail glass instead.