Abstract: A rigid composite body containing crystalline molecular sieves and having liquid-permeable channels extending in a substantially vertical direction from one surface of said body to the interior thereof, preferably to an opposite surface, is charged with carbon dioxide so that when brought in contact with water or an aqueous beverage, the carbon dioxide will be released from the molecular sieve composite body to carbonate the solution. Such rigid, composite bodies are secured in a sealable, nestable, stackable container which provides a convenient and efficient means for dispensing such composite bodies in combination with a dry instant beverage mix for the preparation of carbonated beverages upon the addition of water.