Is slimy sauerkraut safe to eat? (Sauerkraut spoilage)
In this brief guide, we will answer the question “Is slimy sauerkraut safe to eat?”. We also will discuss how the formation of slime occurs and the risks of spoiled sauerkraut.
Is slimy sauerkraut safe to eat?
No, generally it’s not safe to eat slimy sauerkraut, but that doesn’t immediately mean it’s gone bad. Slime or “dextran” can periodically appear in batches of fermenting sauerkraut. This is usually due to bacteria like Leuconostoc mesenteroides or Leuconostoc dextranicum growing in the early stages of fermentation when there’s still sugar present and the pH isn’t too acidic.
Often, this slime goes away as the sauerkraut continues to mature. However, if the sauerkraut continues to be slimy or even gets slimmer, it could mean it’s spoiled and you should probably throw it away. The sudden appearance of glucose in the later stages of fermentation could be due to hydrolysis. (1)
How is the fermentation process of sauerkraut?
The classic sauerkraut fermentation process commences with the initial growth of Leuconostoc mesenteroides, which rapidly generates carbon dioxide and acid. This rapid acidification lowers the pH of the environment, creating conditions unsuitable for the growth of harmful microorganisms that could spoil the food while preserving the cabbage’s color.
The activities of L. mesenteroides transform the fermentation environment to promote the succession of other lactic acid bacteria (LAB), such as Lactobacillus brevis and Lactobacillus plantarum. In traditional sauerkraut production, this transformation occurs at a temperature of approximately 18°C over about one month.
The combination of metabolites produced by these microorganisms contributes to the desirable sensory qualities, including the unique flavors, aromas, and textures associated with fermented foods found in the final product. Additionally, the fermentation temperature plays a crucial role in determining the color, flavor, and shelf-life of the sauerkraut. (2)
Does sauerkraut spoil?
Yes, sauerkraut does spoil. Fermentation serves as a method to prevent the deterioration of cabbage and prolong its shelf life by leveraging the organic acids produced by lactic acid bacteria (LAB) to inhibit the growth of unwanted microorganisms.
However, when there is a high population of microbes, it can lead to the production of potentially harmful metabolites, such as biogenic amines. Biogenic amines are fundamental nitrogen-containing compounds with low molecular weight, possessing biological activity, and when their levels reach 1000 mg/kg in food they are considered harmful to human health.
Sauerkraut made with green cabbage should have a very pale yellow or light beige color, a pleasantly sour and tart taste, a firm, crisp, and crunchy texture, and a pleasantly pungent and sour aroma. (3)
What are the signs of spoilage of sauerkraut?
The main signs of spoilage of sauerkraut are the formation of a surface film, the growth of mold, sometimes, sauerkraut may develop a weird smell that’s similar to rotting organic material, or the taste might become unpleasant. Sauekraut should be discarded in those cases.
Gas pocket formation, changes in color, or changes in the texture like softening are also common signs. This is often caused by oxidative yeasts that eat up the lactic acids produced during fermentation. This results in unwanted changes and a rise in pH levels, which makes it easier for spoilage bacteria to multiply.
The occurrence of pink sauerkraut is one of the most common defects in its production. This pink sauerkraut is a common issue in its production process. Although you can technically still eat it, and some places even sell it cheaper, it tends to affect the sauerkraut’s texture, taste, and smell.
The reason why sauerkraut sometimes turns pink is traced back to the natural yeasts living in the cabbage. These yeasts flourish depending on the amount and kind of sugars present in the cabbage.
It’s essential to keep specific conditions during the lactic acid vegetable fermentation process, like high acidity and low pH levels, to preserve the end product. Still, sometimes unintended secondary fermentation or spoilage might happen. (6)
What factors affect the production of slime?
The generation of slime is affected by various factors, including physical and chemical attributes like solubility, viscosity, specific optical rotation, as well as the levels of nitrogen, phosphorus, and ash in the medium.
These factors are contingent upon the particular microorganisms in question. Factors that can contribute to slime formation include an excess of sugar, low salt concentrations, elevated temperatures, short fermentation periods, and exposure to oxygen. (1, 4)
What are the dangers of spoiled sauerkraut?
Within the category of biogenic amines, it’s understood that histamine and tyramine possess psychoactive and vasoactive characteristics, which can lead to toxicological repercussions.
Elevated levels of histamine can result in symptoms such as headaches, low blood pressure, palpitations, skin disorders, vomiting, and diarrhea, while tyramine has the potential to induce migraines and high blood pressure. (3)
How to store sauerkraut?
Canning or storing sauerkraut in a cool cellar or pantry provides effective options for extended storage without refrigeration. Alternatively, sauerkraut can be stored in the refrigerator at 4°C. The shelf life of sauerkraut can vary depending on the storage method, ranging from as short as a few days to as long as 2 years or more.
Typically, homemade sauerkraut can be safely stored for at least 6 to 12 months. Canned sauerkraut maintains its quality for a minimum of 12 to 18 months. Once opened, canned sauerkraut should be refrigerated and consumed within 3 to 7 days, but it can remain good for up to 1 or 2 months. (5)
In this brief guide, we answered the question “Is slimy sauerkraut safe to eat?”. We also discussed how the formation of slime occurs and the risks of spoiled sauerkraut.
Through my research, I was able to uncover that although slime formation may be a sign of spoilage it is a natural by-product of the fermentation process that happens when there is a high level of sugar present in the sauerkraut. In my perspective as a food scientist, this slime usually disappears after the appropriate amount of fermentation time making sauerkraut safe to consume.
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HUGHES, A.; LINDSAY, R. C. Liquid chromatographic analysis of sugars and mannitol in cabbage and fermenting sauerkraut. Journal of Food Science, v. 50, n. 6, p. 1662-1667, 1985.
ZABAT, Michelle A. et al. Microbial community analysis of sauerkraut fermentation reveals a stable and rapidly established community. Foods, v. 7, n. 5, p. 77, 2018.
PEÑAS, Elena et al. Impact of fermentation conditions and refrigerated storage on microbial quality and biogenic amine content of sauerkraut. Food Chemistry, v. 123, n. 1, p. 143-150, 2010.
DU, Renpeng et al. Optimization, purification and structural characterization of a dextran produced by L. mesenteroides isolated from Chinese sauerkraut. Carbohydrate Polymers, v. 174, p. 409-416, 2017.
U.S. Department of Agriculture. https://ask.usda.gov/ Website. Washington, DC.Shelf-Stable Food Safety. 2023.
MEDINA-PRADAS, Eduardo et al. Review of vegetable fermentations with particular emphasis on processing modifications, microbial ecology, and spoilage. In: The microbiological quality of food. Woodhead Publishing, 2017. p. 211-236.