The first stage of sauerkraut fermentation involves anaerobic bacteria, which is why the shredded cabbage and salt need to be packed in an airtight container. At this stage, the surrounding environment is not acidic, just cabbagey. The bacteria, mostly Leuconostoc species, produce carbon dioxide (replacing the last vestiges of oxygen in the jar) and lactic acid, which is a natural by-product of anaerobic respiration. Eventually, the conditions within the jar become too acidic for these bacteria to survive and they die out, replaced with bacteria that can better handle the acidic conditions such as Lactobacillus species.
The lactobacillus further ferments any sugars remaining in the cabbage, using anaerobic respiration. This produces more lactic acid until the sauerkraut reaches a pH of about 3. These bacteria are inhibited by high salt concentrations (so most sauerkraut contains around 2-3% salt) and low temperatures, which is why the fermenting jars should be left at room temperature rather than in the fridge. At pH3 the lactobacillus stop fermenting and the sauerkraut can be stored until needed.
All these bacteria help to create the tangy acidic taste; however, there are ways that microbial growth can go wrong. Overgrowth of the lactobacillus, for example, if the jar is stored at too high a temperature during fermentation, can cause the sauerkraut to form the wrong consistency. Likewise, if the sauerkraut gets too acidic too early the lactobacillus gets in on the action early leading to soft sauerkraut. Although the finished sauerkraut is far too acidic for pathogens to live in, fungal spores may settle on the surface and spread, spoiling the food.
Although sauerkraut is a German word, the dish is thought to have originated in China with cabbage fermented in rice wine or brine. This spread to Europe by way of Ghengis Khan’s invaders where the cabbage was dry-cured with salt. As sauerkraut keeps for long periods and is a source of vitamin C, it was favoured by the Dutch sailors, who took it with them when they travelled to America. Captain Cook also travelled with it to Australia, as sauerkraut contains a range of vitamins and minerals that are difficult to obtain when travelling for long periods at sea.
As the bacteria required for sauerkraut fermentation are found on the cabbage leaves, it’s a very easy and healthy dish to produce. All you need is cabbage! By exploiting the actions of bacteria simple ingredients such as cabbage and salty water can be used to produce a healthy dish that can be stored long past the time when raw fruit and vegetables will have begun to spoil.