The present invention provides improved methods for producing a solution containing high molecular weight isolated Streptococcus pneumoniae 19A capsular polysaccharides. In certain methods, a fermentation culture of Streptococcus pneumoniae bacterial cells that produce serotype 19A capsular polysaccharides is femiented for less than 6 hours before the bacterial cells are lysed the capsular polysaccharides are harvested. In other methods, CO2 is supplied to the fermentation culture. Supplying CO2 to the fermentation culture includes adding bicarbonate ions to the fermentation culture, adding carbonate ions to the fermentation culture, adding mixtures of bicarbonate and carbonate ions to the fermentation culture, and overlaying the fermentation culture with CO2.
