Starbucks’ customers in Atlanta, Austin, Singapore, and Japan have recently been part of a carbonation experiment.

On the heels of the Sodastream’s rise in popularity – and following research suggesting customers prefer lighter, more refreshing drinks later in the day – Starbucks began planting Sodastream-like carbonation machines in certain stores to test the popularity of a new hand-crafted soda line. The line includes lemon ale, ginger ale, and spiced root beer.

Somewhat unexpectedly, customers began asking baristas to add fizz to other beverages as well, including coffee and tea. Starbucks eagerly obliged, and customer feedback was positive. The company hasn’t yet figured out how to carbonate espresso drinks or Frappuccinos, but it’s probably safe to guess that it’s working on solutions.

CEO Howard Schultz has said carbonation will be the company’s new category, and the coffee giant has taken steps to trademark the name Fizzio for its new carbonation line. While the plans to actually launch the line in stores are still unofficial, insiders are speculating that carbonation will soon be a run-of-the-mill customization option for Starbucks’ customers.