Why Does Bubble Tea Foam When Shaken? Causes and Tips If you have ever ordered or prepared bubble tea and noticed a layer of bubbles or foam on top after shaking, you may wonder why it happens. Why does bubble tea foam when shaken? In most cases, the answer is simple: shaking mixes the ingredients while also incorporating air into the drink. The amount and appearance of foam can vary depending on the ingredients, temperature, shaking method, and type of bubble tea. Milk tea a