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Asked by dgsmigliani ·October 1, 2022 ·13.6k readers

LAB mold on surface

Hi everyone, I've recently made a batch of LAB and have it stored in a 100L water tank with equal parts LAB to unsulphured molasses (roughly 2L each of LAB/molasses). It's been a few weeks now and i've noticed some mold growth on the surface? Can anyone please help explain why this is occurring and if it's still okay? Thank you! Links to images

https://ibb.co/VDX9pn8 https://ibb.co/2yjPJxW

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mold lab

The answer

From the KNF library

From the KNF library Drafted by Claude from Office Hours and the books · Sep 2026 · 3 sources

Drake's office hours give two reasons for mold on top of a LAB ferment: too much airspace, and not enough sugar. (Office Hours Ep. 49, 16:27)

Check the sugar first. The Basic Course recipe says the wooden spoon should float when there is enough sugar. (Student's Manual, Basic Course, p. 17) The UH–CTAHR fact sheet says to store LAB at room temperature with an equal amount of brown sugar, by weight. (Student's Manual, Basic Course, p. 15)

Then smell it. The fact sheet says LAB should smell sweet. If it turns rotten, discard it and make a new batch. (Student's Manual, Basic Course, p. 15)

The library does not cover molasses as the storage sugar, a 100 L tank, or how to judge the mold in your photos.

Sources

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