Commonly used yeast is said to contain something in the range of a few micrograms of biotin per gram (1). Yeast extracts from sourdough contain MILLIgrams of biotin per gram dry weight (2). How does this work? If yeast has ~70% water content, that makes up for only a small portion of this differences. Also, if the yeast extract does not contain the cell wall weight, that also makes up for a small portion as the cell wall weight is somewhere in the vicinity of 50%, according to google ai. Shouldn't the yeast extract have biotin concetrations maybe like 2-3 times as high as yeast, not more than 1000 times higher?

Does the yeast accumulate biotin during fermentation in sourdough? Does the yeast accumulate biotin during beer fermentation? Does it produce the biotin?

If sourdough bread yeast extract contains so much biotin, how come bread with several % sourdough and/or yeast still only contains a few micrograms of biotin per 100g (3, 4)? Mathematically speaking, shouldn't the yeast extract have biotin concentrations maybe 2-3 times as high as yeast, not 1000 times higher? And if sourdough yeast extract has MILLIgrams of biotin per gram, and bread contains several % sourdough/yeast, shouldn't 100 g bread contain several MILLIgrams of biotin?

1. https://journals.asm.org/doi/pdf/10.1128/jb.58.1.33-44.1949
2. Demirgül et al. "Amino acid, mineral, vitamin B contents and bioactivities of extracts of yeasts isolated from sourdough" Food Bioscience 50(3):102040 https://www.sciencedirect.com/science/article/abs/pii/S2212429222005004
3. https://plaza.umin.ac.jp/e-jabs/2/2.109.pdf
4. https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/#h3