Changes

Cheaper methods of doing PCR are recently becoming available, and could help breweries with smaller budgets sufficiently detect this as a contaminant (see [[Laboratory_Techniques#PCR.2FqPCR|PCR Lab Techniques]]). A recent study used agar plates with 15 g/L^-1 of starch as the only nutrient with 40 mg/L^-1 bromophenol blue in anaerobic conditions to detect the fermentation of starch (a pH drop from 5.2 to 4.6-3.0 will change the color of the agar plate to blue/violet). For some of the slower growing strains, 14 days were required to verify that they were ''STA1+'' while other strains grew as quickly as two days and most strains grew after five days. The yeast cells had to be thoroughly washed of all other carbohydrate material and starved in order to avoid false positives. Using dextrin agar plates instead of starch also led to false positives <ref name="Meier-Dörnberg_2018" />. This starch media has been recommended by Richard Preiss from [[Escarpment Laboratories]] and Justin Amaral from [[Mainiacal Yeast]] <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2149139905114212/?comment_id=2150763631618506&comment_tracking=%7B%22tn%22%3A%22R%22%7D Richard Preiss and Justin Amaral. Milk The Funk Facebook thread on plate media for diastatic ''cerevisiae''. 06/26/2018.]</ref>. Note that diastatic ''S. cerevisiae'' cells look the same under a microscope as regular ''S. cerevisiae'', so cell morphology is not an effective way to identify ''STA1+'' strains <ref name="Begrow_MBAA">[https://www.mbaa.com/education/webinars/Pages/webcast.aspx?vid=diastaticus Wade Begrow. "S. cerevisiae var. diasttaicus". MBAA webinar. July 2018.]</ref> (~8 minutes in). Other methods of detection include using a Durham tube/fermentation tube test to see if the beer produces CO² after fermentation, although this method does not identify the cause of the additional fermentation <ref name="Begrow_MBAA" /> (~18 mins in). More recently, Krogerus et al. (2019) developed more precise PCR primers to detect ''STA1'' active, ''STA1'' non-active, and non-''STA1'' based on their discovered role of an ''STA1'' promoter called ''1162 bp'' that is required for the ''STA1'' gene to be effective at producing the glucoamylase enzyme, however, PCR and qPCR have limited detection rates of 10^-4 and 10^-5 cells (see [http://beer.suregork.com/?p=4068 this Suregork Loves Beer blog post] and [https://www.facebook.com/groups/MilkTheFunk/permalink/2697088176986046/ this MTF thread posted by Kristoffer Krogerus]).

Detection of ''STA1+'' strains of ''S. cerevisiae'' as a contaminant can be difficult. While using PCR to detect the ''STA1'' gene and the promoter gene, the presence of the promoter gene alone does not completely explain the wide variance of diastatic power between strains. Additionally, PCR genotyping is sucseptable to user error or DNA detection from dead cells. Detection of the presence of starch degrading enzymes can come from other contaminants such as ''Brettanomyces'' <ref name="Omega_diastaticus_2020" />. Some agar media products and even starch/dextrin materials have been suspected to contain small amounts of glucose or other simple sugar contaminants that can support the growth of non-diastatic yeasts <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/3308119659216225/ Lance Shaner and Joshua Mayers. Milk The Funk Facebook thread on Omega Yeast's STA1+ detection methods. 03/04/2020.]</ref>. [[Omega Yeast Labs]] reported that a slight alteration to the classic LCYM media recipe had significantly more reliable detection than classic LCYM and the proprietary Weber diastatic agar for all ''STA1+'' strains in Omega's collection, including detecting slow growing strains within 2-3 days and strains with the non-active promoter genes as per Krogerus et al (2019) and limited false positives. See [[Laboratory_Techniques#Saccharomyces|''Saccharomyces'' agar plates]] for the recipe and [https://www.facebook.com/groups/MilkTheFunk/permalink/2874530432575152/ this MTF thread] by Laura Burns from Omega Yeast Labs, as well as their [https://omegayeast.com/news/improved-functional-assays-and-risk-assessment-for-sta-strains-of-saccharomyces-cerevisiae associated peer reviewed study on recommended detection methods)] <ref>[https://www.tandfonline.com/doi/full/10.1080/03610470.2020.1796175 Laura T. Burns, Christine D. Sislak, Nathan L. Gibbon, Nicole R. Saylor, Marete R. Seymour, Lance M. Shaner & Patrick A. Gibney (2020) Improved Functional Assays and Risk Assessment for STA1+ Strains of Saccharomyces cerevisiae, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2020.1796175 .]</ref>. A summary of the Omega Yeast Lab detection methodology findings by Lance Shaner is available [https://www.facebook.com/groups/MilkTheFunk/permalink/3308119659216225/ here on MTF]. Escarpment Labs built upon the work by Burns et al. and developed a modified version of the Omega LCYM, and they reported it to have less false positives for non-diastatic strains and it has reportedly been used for growing beer strains of ''Brettanomyces'' and ''Pichia''. See the [[Laboratory_Techniques#Saccharomyces|Escarpment SCCM media]].