Before frozen foods, refrigeration, and cheap transport from warmer areas became readily available in northern, central and eastern Europe, sauerkraut - like other preserved foods - provided a source of nutrients during the winter. Captain James Cook always took a store of sauerkraut on his sea voyages, since experience had taught him it prevented scurvy.
The word "Kraut", derived from this food, is a derogatory term for the German people. During World War I, due to concerns the American public would reject a product with a German name, American sauerkraut makers relabeled their product as "Liberty Cabbage" for the duration of the war.
Sauerkraut is made by a process of pickling called lactic acid fermentation that is analogous to how traditional (not heat-treated) pickled cucumbers and kimchi are made. The cabbage is finely shredded, layered with salt, and left to ferment. Fully cured sauerkraut keeps for several months in an airtight container stored at 15 °C (60 °F) or below. Neither refrigeration nor pasteurization is required, although these treatments prolong storage life.
Fermentation by lactobacilli is introduced naturally, as these air-borne bacteria culture on raw cabbage leaves where they grow. Yeasts also are present, and may yield soft sauerkraut of poor flavor when the fermentation temperature is too high. The fermentation process has three phases, collectively sometimes referred to as population dynamics. In the first phase, anaerobic bacteria such as Klebsiella and Enterobacter lead the fermentation, and begin producing an acidic environment that favors later bacteria. The second phase starts as the acid levels become too high for many bacteria, and Leuconostoc mesenteroides and other Leuconostoc species take dominance. In the third phase, various Lactobacillus species, including L. brevis and L. plantarum, ferment any remaining sugars, further lowering the pH. Properly cured sauerkraut is sufficiently acidic to prevent a favorable environment for the growth of Clostridium botulinum, the toxins of which cause botulism.
A 2004 genomic study found an unexpectedly large diversity of lactic acid bacteria in sauerkraut, and that previous studies had oversimplified this diversity. Weissella was found to be a major organism in the initial, heterofermentative stage, up to day 7. It was also found that Lactobacillus brevis and Pediococcus pentosaceus had smaller population numbers in the first 14 days than previous studies had reported.
The Dutch sauerkraut industry found that inoculating a new batch of sauerkraut with an old batch resulted in an excessively sour product. This sourdough process is known as "backslopping" or "inoculum enrichment"; when used in making sauerkraut, first- and second-stage population dynamics, important to developing flavor, are bypassed. This is due primarily to the greater initial activity of species L. plantarum.
Eastern European-style sauerkraut pickled with carrots and served as a salad
In Azerbaijani, Belarusian, Polish, Russian, Baltic states and Ukrainian cuisine, chopped cabbage is often pickled together with shredded carrots. Other ingredients may include caraway seeds, whole or quartered apples for additional flavor or cranberry for flavor and better keeping (the benzoic acid in cranberries is a common preservative). Bell peppers and beets are added in some recipes for colour. The resulting sauerkraut salad is typically served cold, as zakuski or a side dish. A home made type of very mild sauerkraut is available, where white cabbage is pickled with salt in a refrigerator for only three to seven days. This process results in very little lactic acid production. Sometimes in Russia the double fermentation is used, with the initial step producing an exceptionally sour product, which is then "corrected" by adding 30-50% more fresh cabbage and fermenting the mix again. The flavor additives like apples, beets, cranberries and sometimes even watermelons are usually introduced at this step.
If unpasteurized and uncooked, sauerkraut also contains live lactobacilli and beneficial microbes and is rich in enzymes. Fiber and probiotics improve digestion and promote the growth of healthy bowel flora, protecting against many diseases of the digestive tract.
During the American Civil War, the physician John Jay Terrell (1829-1922) was able to successfully reduce the death rate from disease among prisoners of war; he attributed this to feeding his patients raw sauerkraut.
Sauerkraut and its juice is a time-honored folk remedy for canker sores. The treatment is to rinse the mouth with sauerkraut juice for about 30 seconds several times a day, or place a wad of sauerkraut against the affected area for a minute or so before chewing and swallowing the sauerkraut.
In 2002, the Journal of Agriculture and Food Chemistry reported that Finnish researchers found the isothiocyanates produced in sauerkraut fermentation inhibit the growth of cancer cells in test tube and animal studies. A Polish study in 2010 concluded that "induction of the key detoxifying enzymes by cabbage juices, particularly sauerkraut, may be responsible for their chemopreventive activity demonstrated by epidemiological studies and in animal models".
One of the early scientists who was involved in identifying the biology and function of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), Philippe Horvath, focused on the genetics of a lactic-acid bacterium used in the production of sauerkraut.
Many other vegetables are preserved by a similar process:
^Saloheimo P (2005). "[Captain Cook used sauerkraut to prevent scurvy]". Duodecim (in Finnish). 121 (9): 1014-5. PMID15991750.
^Oxford English Dictionary. Second edition, 1989. "1. = SAUERKRAUT, SOURCROUT. Also attrib. and Comb. 2. (Often with capital initial.) A German, esp. a German soldier. Also attrib. and Comb. Derogatory."
^Moret, Sabrina; Smela, Dana; Populin, Tiziana; Conte, Lanfranco S.; et al. (2005). "A survey on free biogenic amine content of fresh and preserved vegetables". Food Chemistry. 89 (3): 355-361. doi:10.1016/j.foodchem.2004.02.050.
^Pu, C.; Xia, C; Xie, C; Li, K; et al. (November 2001). "Research on the dynamic variation and elimination of nitrite content in sauerkraut during pickling". Wei Sheng Yan Jiu. 30 (6): 352-4. PMID12561618.