Why Does Shaken Soda Spray When Opened?

Carbon dioxide in soda is not merely ‘stored in the bottle’. A large amount is dissolved in the liquid under pressure. While the bottle is sealed, gas above the drink, dissolved carbon dioxide and a small number of bubbles remain in a dynamic balance. Opening the cap lowers the pressure, so the liquid can no longer hold as much carbon dioxide and gas begins to escape.

Shaking matters because it creates and disperses many tiny bubbles through the liquid and along the bottle wall. These bubbles already provide spaces where gas can collect, so carbon dioxide does not have to form entirely new bubbles in otherwise uniform liquid. When the cap opens and pressure suddenly falls, the existing bubbles expand and rise. Many bubbles moving through the drink at once act like small pistons, carrying liquid towards and through the opening.

Shaking therefore does not manufacture extra carbon dioxide, and the spray is not mainly caused by centrifugal force. Letting the bottle stand gives small bubbles time to rise and join the gas space above the liquid. Cooling also increases the solubility of carbon dioxide in water. The safest response is to let the bottle settle and open it slowly so pressure is released gradually, rather than trusting a tap on the container to prevent a spray.

https://www.acs.org/education/whatischemistry/adventures-in-chemistry/secret-science-stuff/soda-pop.html
https://van.physics.illinois.edu/ask/listing/623