This is the second time I'm doing a no-boil, fast lacto sour. I had nearly 3 lbs of grain (with about 9% acid malt) for a 1 gallon batch. I did BIAB for 1 hour and put right into a fermenter. I let it cool down to about 100 °F and pitched 2 pills of Lactobacillus plantarum from Swanson Probiotics. It sits in a room without A/C, so the heat remains fairly high especially now with a heat wave in Southern California. Day 2 I added 2 more lacto pills.

Here is a pic from day 3, which looks fairly normal:

Normal Picture

On day 4, I noticed a patch of cotton-looking growth at the top left of this picture (hard to notice):

Cotton-looking growth at the top left

pH dropped from 4.54 on day 1 to 3.57 on day 4. I tasted a little sample from day 4 and I can taste the sourness. The smell seems normal: there is no vomit, fecal smell, but rather earthiness.

Should I remove that cotton growth? Keep it and boil? Just let it go normally? Last year I did this same method (BIAB, no boil, lacto, saison yeast, dry hop) but with L. delbrueckii and had a great success. But with this cotton thing, I'm slightly concerned.

  • Executive decision: I forgot a low pH may negatively affect yeast, so I pitched WLP565. Looks like boiling is off the table. Mar 16, 2017 at 23:32
  • How was the pH measured? Probe or paper (or what)? Mar 20, 2017 at 10:00
  • A digital pH meter. Just checked it today: some sulfur smell, but it looks more like normal S. cerevisiae is on top. Mar 22, 2017 at 3:59

1 Answer 1


IMHO mould growth is not often fatal to brewing but you should remove the fungal mycelium, preferably before it spores, with (e.g.) a spoon and continue fermentation. Seems like a lot of air/head space above the brew in the bucket. Maybe worth using a smaller container to assist the build up of CO2 and make the protective "gas blanket" that CO2 provides.

  • Yup, did that just this morning. It had turned grey, but was easy to scoop out. It was resting on top of the lacto "carpet". I did see some bubbles popping underneath the lacto, so it appears the yeast is beginning to work. Mar 17, 2017 at 20:07

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