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Five Star Chemicals product Star San is a popular acid anionic sanitizer sold to homebrewers because of its relative safety and ease of use. Claims that acid anionic sanitizers are not effective at killing yeast have been made on various internet forums <ref>[https://www.homebrewersassociation.org/forum/index.php?topic=24447.msg312961#msg312961 User 'S. cerevisiae'. American Homebrewers Association forums. 10/05/2015. Retrieved 04/11/2018.]</ref><ref>[https://www.homebrewersassociation.org/forum/index.php?topic=4576.msg52894#msg52894 User 'richardt'. American Homebrewers Association forums. 11/15/2010. Retrieved 04/11/2018.]</ref>. These claims are based on the food science textbooks, "Principles of Food Sanitation," by Norman G. Marriott and Robert B. Gravani (2006) and "Basic Food Microbiology" by George Banward (1989), which contain conflicting information about the effectiveness of acid anionic sanitizers, and neither source contains experimental data nor references to experimental data. Furthermore, the provided explanation, which is that acid anionic sanitizers supposedly don't work effectively against yeast and molds is because acid anionic sanitizers are negatively charged and yeast are also negatively charged yet bacteria is killed because it is positively charged, is biologically incorrect. According to [https://www.youtube.com/watch?v=0JC9n50RdVo Dr. Bryan Heit of Sui Generis blog], both yeast and bacteria have negatively charged cell walls, and this fact has been well established in microbiology since the 1940's (Dr. Heit has published several [https://scholar.google.com/citations?user=8yxqYNgAAAAJ&hl=en&oi=ao peer-reviewed scientific studies on cell wall polarity]).
While we are not aware of any publicly available published studies on the efficacy of StarSan, several studies with other acid anionic sanitizers have confirmed that they are effective against non-spore forming yeast. [https://onlinelibrary.wiley.com/doi/full/10.1111/j.1750-3841.2007.00496.x Lee et al . (2007)] found that an acid sanitizer very similar to Star San that uses citric acid instead of phosphate but the same surfactant (sodium dodecylbenzene sulfonate) took 5 minutes to kill ''Saccharomyces cerevisiae'', ''E. coli'', and ''Listeria innocua'' at room temperature (some species were killed faster than others with the ''E. coli'' actually being more resistant than the yeast), and one minute if the sanitizer was heated to 40°C on both metal and LDPE plastic (they compared the acid anionic sanitizer to 35% hydrogen peroxide, which killed all organisms with 15 seconds, indicating that this acid anionic sanitizer is effective at killing yeast, but it takes longer than a stronger chemical such as hydrogen peroxide). This study did not make mention of biofilms, however, the cultures were allowed to grow and dry overnight <ref>[https://onlinelibrary.wiley.com/doi/full/10.1111/j.1750-3841.2007.00496.x Efficacy of Two Acidic Sanitizers for MicrobialReduction on Metal Cans and Low-Density Polyethylene Film Surfaces. J. L EE , M.J. G UPTA , J. L OPES , AND M.A. P ASCALL. 2007.]</ref>. Five star [http://www.fivestarchemicals.com/wp-content/uploads/Star-San-HB4.pdf also recommends 5 minutes of contact time with Star San]. Winniczuk et al. (1997) found that three phosphoric acid anionic sanitizers ("CS-100" and "CS-101-lf" by Chemical Systems of Florida, and "Clear-Clean" by Pelican Brand) were less effective at killing yeast than bacteria in the timeframe tested (1 minute contact time), but they were still effective at killing yeast high concentrations (peracetic acid also required a higher concentration to kill yeast than bacteria). However, one of the acid anionic sanitizers tested was more effective than the other two, indicating that the chemical makeup of the particular acid anionic sanitizer has an impact on how effective it is as a sanitizer relative to other acid anionic sanitizers. Additionally, they found that peracetic acid, iodophor, and chlorine dioxide required less concentration than the acid anionic sanitizers to be effective (again, tested at 1 minute exposure time) <ref>[http://lp7lc5er8n.scholar.serialssolutions.com/?sid=google&auinit=PP&aulast=Winniczuk&atitle=Minimum+inhibitory+concentrations+of+antimicrobials+against+micro-organisms+related+to+citrus+juice&id=doi:10.1006/fmic.1997.0103&title=Food+microbiology&volume=14&issue=4&date=1997&spage=373&issn=0740-0020 Minimum inhibitory concentrations of antimicrobials against micro-organisms related to citrus juice. P.P Winniczuk, M.E Parish. 1997.]</ref>.
See [https://www.facebook.com/groups/MilkTheFunk/permalink/1436419659719577/ this MTF thread] for a more extensive explanation of why skepticism should be applied to the claim that acid anionic sanitizers are not effective at killing yeast.