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Sauerkraut: bacteria making food

The views expressed are those of the author and are not necessarily those of Scientific American.


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Last week my husband needed some jars for cooking purposes. Tesco sell jars for somewhere around £3 each. However they also sell large jars full of sauerkraut for £1 each. Which means that last weekend we had an awful lot of sauerkraut to try and get through.

This much sauerkraut! (SPOILER: we didn't manage it)

I’m not a great fan of sauerkraut, which is a pity because most of the taste comes from the action of bacteria. Not just one bacteria either, but a whole range of different species are involved in the fermentation process. The bacteria don’t even need to be added to the sauerkraut, as they live naturally on the cabbage leaves. All that is required to start the process off is shredded cabbage and salt.

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 byproduct 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.

Homemade sauerkraut fermenting in jars - image from Gandydancer on wikimedia commons.

The lactobacillus further ferment 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 the 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 get 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.

Frankfurter Rippchen (cured pork cutlet) with sauerkraut. By dontworry uploaded to wikimedia commons.

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.

S.E. Gould About the Author: A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. Follow on Twitter @labratting.

The views expressed are those of the author and are not necessarily those of Scientific American.





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