White coating on sauerkraut: Safe sign of fermentation or mould?

Don't throw away sauerkraut if you notice a white coating on it. First, take a close look at it. It's highly likely that the coating covering the sauerkraut is not mould but rather a sign of successful fermentation.

It may cause concern because it resembles mould, and as we know, we shouldn't eat mouldy products, even if we remove the harmful coating. Usually, however, the white layer found on sauerkraut, cucumbers, or homemade vinegar is a fermentation film that indicates the fermentation process is going well.

The fermentation film forms as a result of the natural lactic acid fermentation process, which occurs under the influence of lactic acid bacteria. We could say it's a by-product of fermentation that forms a thin layer over the sauerkraut. It's safe for the preserved foods and our health, so we don't need to worry about it. However, it is recommended to remove the fermentation film from the surface of the sauerkraut or stir it in because it could lead to quicker spoilage.

To some people, a fermentation film might look like mould. And this should be a cause for concern. Distinguishing one from the other might seem challenging, but it's enough to know what to look for to determine whether the sauerkraut is covered in mould or fermentation film.

Firstly, mould appears in clumps (resembling fur). It also takes on various colours – from white to grey, blue, and even orange. It's more problematic if we're dealing with white mould. Then, it can be distinguished from the fermentation film by its texture, as mould is not homogeneous, whereas the fermentation film is milky white and uniform. Additionally, mouldy sauerkraut develops a characteristic, musty smell. On the other hand, if the sauerkraut is sour and salty and has a pleasant smell, it is certainly safe to eat.