This is a guest blog post by Tessa, one of our Spring 2015 Evergreen interns, about how fermentation works on a microbial level.

Kraut in the Crock—Idle moments for humans, hectic for bacteria.

After much practice, reading and observation, OlyKraut has been able to consistently produce high quality-- unpasteurized, probiotic rich, consistent, flavorful- sauerkraut. Olykraut employees set up an ideal environment for the resident bacteria to carry out fermentation in the crocks. Temperature and salt are the two factors that help control what happens during the 6 week fermentation period. Distribution of salt throughout the sauerkraut and a temperature between 60-65°F encourage an important succession of bacterial species. Salt inhibits fermentation, or bacterial activity, as well as temperatures below 45°F. Sauerkraut will still result with higher salt and/or lower temperatures but a significant (half a year) time period is needed to carry out the bacterial process which results in a desirable product. So, what is happening on the microscopic level?

When the cabbage and salt (and any other additions) are mixed and tamped (firmly packed) in the crock fermentation begins. By firmly packing the vegetable matter oxygen is pushed out and cabbage juice is pulled out- through osmosis and a little roughing up.  This creates an anaerobic environment that is conducive for Leuconostoc mesenteroides. These heterofermentative bacteria are responsible for much of the flavor profile in the sauerkraut. During their metabolic processes these bacteria produce carbon dioxide bubbles that rise and expel any remaining oxygen. As the population of L. mesenteroides grows they also emit lactic acids, ethyl alcohol and acetic acid. The sour taste that is associated with sauerkraut is a result of the organic acids produced which causes a drop in pH, or increase in hydrogen ion concentration.  After a few days the lactic acid concentration rises and restricts the continued growth of Leuconostoc mesenteroides. The environment surrenders to the control of Lactobacillus plantarum- an acid loving bacterium.

L plantarum is responsible for the rapid decrease in pH, or increase in acidity. These homofermenters convert the sugars in the cabbage to lactic acid in the anaerobic environment. Once this lactobacillus has become established the large vats of sauerkraut are packed into the small jars and refrigerated. Fermentation does not stop here, but is slowed drastically. There is still sugar in the cabbage for the bacteria, such as Lactobacillus pentaocetus and Lactobacillus brevis, to metabolize. If smaller containers are packed too soon unwanted explosions could happen due to carbon dioxide buildup from a very active ferment with lots of sugars to digest. Mishaps in fermentation are to be expected, and can yields some unexpected results- wanted or not.

OlyKraut uses mostly stainless steel wine fermenters and a few ceramic crocks to avoid fermenting in plastic for health and quality reasons.  Sauerkraut should not be fermented in a reactive metal like copper or aluminum, but high grade stainless steel produces a clean, delicious product.  If you are interested in fermenting vegetables at home, OlyKraut loves InFerment's handmade stoneware crocks.   And if you are interested in yeast fermentation for alcohol, like in beer or wine, you can check out these beer fermenters if you want to know more about them.

References

"Meats and Sausages." Sauerkraut Fermentation. N.p., n.d. Web. May 2015.

"The Science Behind Sauerkraut Fermentation." Nourishing Treasures. N.p., n.d. Web. May 2015.