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There is a pink scum on top of the brine of my sauerkraut in the crock. What is it & is it harmful? Bev

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If you're seeing pink scum, it's probably a yeast called Hanseniaspora uvarum. This yeast can make a pink or reddish film on the surface of the sauerkraut during fermentation.

Typically this yeast will grow from one or more of these causes:

  1. Too little salt: while salt is not actually necessary to ferment vegetables, it adds flavor; denatures pectinase (the enzyme that breaks down pectins), keeping the vegetables crisper; and discourages growth of molds and fungi like the yeast you're seeing.

  2. Too much oxygen: yeast is facultative, meaning that it can respirate or ferment (use oxygen or metabolize without oxygen). Fermentation, strictly speaking, is a type of anaerobic metabolism where glucose is broken down into two pyruvate molecules releasing a small amount of energy. If you haven't submerged the vegetables fully in water and/or have the vegetables in an environment where air (containing oxygen) is allowed in, that can cause this yeast to grow. The yeast will also grow in an anaerobic environment, but much more slowly.

If your environment favors the LAB and discourages the yeast, it should not grow.

This yeast is not harmful, so I recommended you carefully take it off the top of your sauerkraut, make sure you have the remaining vegetables submerged, and remove the oxygen from your jar before continuing the ferment.

When you start your ferment there will be oxygen in your jar, and facultative bacteria and yeast will metabolize using it, creating some CO2, which should displace the oxygen if you have a one-way valve. If your jar is sealed the O2 should be used up. After this point your vegetables should only be able to ferment since there is no O2 left. If you open the jar to check on it, you'll once again allow respiration to take place.

LAB likes more a more acidic environment, and the more lactic acid that is created the more your environment will be suitable to its survival, and it will be less hospitable to undesired organisms.

In short, if you set up your ferment properly, you should never have a problem. But if you do see something else growing on top, it's probably safe, but if it's pink and fuzzy that could be a type of mold that produces mycotoxins, so that is not safe to eat.

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This is scum from yeasts in the fermentation. Apparently the sauerkraut is still safe to eat.

This site from Colorado State University on making sauerkraut says:

Ferment:

  1. Place packed container on a tray or plate to catch liquid that may leak fluid leaks out, do NOT pour leaked juice back in, but clean immediately to limit potential contaminants.

  2. Place container in a well—ventilated location (it will have a sour odor) with a relatively constant temperature of 68—72°F, for about 7—14 days. Sauerkraut will ferment faster in warmer temperatures and slower in cooler temperatures.

  3. After bubbling stops (usually about 2—3 days) check that the cabbage is fully submerged under brine. If needed, with clean hands, push cabbage down to draw out more brine. If there is not enough brine to cover the cabbage, stop fermenting at room temperature and refrigerate.

  4. A white or pink yeast scum can appear on the surface at any point in the sauerkraut fermentation process which can be removed and discarded. The sauerkraut below is still edible

Copyright 2020 Food Smart Colorado. https://foodsmartcolorado.colostate.edu/recipes/preservation/understanding-and-making-sauerkraut/ Site accessed 8 March 2024

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