This oxidation relies on a combination of chemically and microbiologically catalyzed processes. Commercial African sorghum beer is packaged in a microbiologically active state. Kobrin, G., "A Practical Manual on Microbiologically Influenced Corrosion", NACE, Houston, Texas, USA, 1993. Compared to malic and citric acids, tartaric acid is usually considered microbiologically stable. Cleanrooms are microbiologically assessed through environmental monitoring methods.