A fermentor for study of sauerkraut fermentation

Abstract

A fermentor was designed and constructed for study of the physical, microbiological, and chemical changes that occur during the sauerkraut fermentation. The fermentor has some essential features that include restriction in volume of the sauerkraut bed, construction of clear plastic to permit visual determination of liquid-level changes as a result of gas entrapment within the sauerkraut bed, and a gas-lift device for use in nitrogen purging of the fermenting brine. Fermentations exhibited two distinct stages, the first one gaseous and the second non-gaseous. The gaseous stage was characterized by rapid CO₂ and acid production due to growth by hetero-fermentative lactic acid bacteria with resultant gas entrapment within the sauerkraut bed and a rise in liquid level. Also, rapid disappearance of fructose and rapid appearance of mannitol occurred during this stage. The nongaseous stage was characterized by growth of homo-fermentative lactic acid bacteria with little or no CO₂ production and a gradual increase in lactic acid until all fermentable sugars were metabolized. Nitrogen purging appeared to offer several potential advantages, including a means for brine circulation, removal of CO₂ from the brine, and anaerobiosis to ensure retention of ascorbic acid, desirable color, and other oxygen-sensitive traits in sauerkraut.