An improvement in a pressurizable container used to prepare a carbonated beverage from a water-based liquid and carbon dioxide generating chemical reactants comprises the use of a carbonation chamber having an upper compartment for holding the chemical couple and a lower compartment with a bottom sparger surface for releasing, as uniformly small bubbles, the generated carbon dioxide into a beverage to be carbonated. The bottom sparger surface permits the rapid carbonation of a beverage without agitation and also minimizes the transfer of the resultant products of the chemical reaction to the beverage.