Lactic Acid Fermentations: SAUERKRAUT

Lactic acid fermentation of cabbage and other vegetables is a common way of preserving fresh vegetables in the western world, China, and Korea (where kimchi is a staple in the diet). It is a simple way of preserving food: the raw vegetable is sliced or shredded, and approximately 2 percent salt is added. The salt extracts liquid from the vegetable, serving as a substrate for the growth of lactic acid bacteria. Anaerobic conditions should be maintained, insofar as
possible, to prevent the growth of microorganisms that might cause spoilage.

The sequence of organisms that develop in a typical sauerkraut fermentation is as follows: Leuconostoc mesenteroides initiates the growth in the shredded cabbage over a wide range of temperatures and salt concentrations. It produces carbon dioxide and lactic and acetic acids, which quickly lower the pH, thereby inhibiting development of undesirable microorganisms that might destroy crispness. The carbon dioxide produced replaces the air and facilitates the anaerobiosis required for the fermentation. The fermentation is completed in sequence by Lactobacillus brevis and Lb. plantarum. Lb. plantarum is responsible for the high acidity. If the fermentation temperature or salt concentration is high, Pecicoccus cerevisiae develops and contributes to acid production.

As would be expected, the rate of completion of the fermentation depends on the temperature and salt concentration. At 7.5°C fermentation is very slow: under these circumstances, L. mesenteroides grows slowly, attaining an acidity of 0.4 percent in about 10 days and an acidity of 0.8 to 0.9 percent in a month. Lactobacilli and pediococci cannot grow well at this temperature, and the fermentation may not be completed for 6 months. At 18°C a total acidity (as
lactic acid) of 1.7 to 2.3 percent will be reached, with an acetic to lactic acid ratio of 1:4, in about 20 days. At 32°C a similar activity will be reached in 8 to 10 days, with most of the acid being lactic acid produced by the homofermentative bacteria Lb. plantarum and P. cerevisiae.

Increasing the salt concentration to 3.5 percent results in 90 percent inhibition of growth and acid production for both L. mesenteroides and Lb. brevis. The ratio of nonvolatile to volatile acid produced has a marked effect on flavor, Lb. brevis producing a harsh, vinegar-like flavor and L. mesenteroides a mild, pleasantly aromatic flavor. The homofermenters Lb. plantarum and P. cerevisiae yield unacceptable products.