Brewers yeast is especially rich in b vitamins and has other nutritional constituents that has endeared itself as a valuable food supplement. Many people use brewers yeast added into smoothies or other foods they are ingesting. However, recent German research shows 90% of 46 samples of brewers yeast contained a mold toxin called ochratoxin A. The amounts ranged from 0.01 ug/kg - 4.2 ug/kg. There are no maximum levels for OTA in nutritional supplements such as brewers yeast, but the researchers recommended brewers yeast should be analyzed for mycotoxins in the future as part of a quality control check.
This is bad news for folks with mold sensitivities that use brewers yeast. Some people have trouble removing mycotoxins (the toxins made by molds) from their body after exposure to a moldy environment. These people take "binders" such as cholestyramine, charcoal, clay, yeast cell walls, probiotics etc. to help remove mycotoxins as they pass through the gut during enterohepatic circulation.
Some strains of brewer's yeast are known to be capable of acting as a mycotoxin binder. The very fact that it bind mycotoxins means it is more likely to have mycotoxin contamination if it came in contact with mold at any point during it's processing or storage. The take home for me here, is that anyone who uses binders for mycotoxins needs to be careful that they are free of mycotoxins when they ingest them. I had some clay that had been in storage for a long time and found when I opened it up that it smelled revolting to me. I was stupid enough to taste it and it ended up making me sick. So, lesson be learned. Mind your nose.