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''Saccharomyces cerevisiae'' var. ''diastaticus'' is a variant of ''S. cerevisiae'' that can ferment certain types of starches and dextrins, and has been identified as a contaminant in breweries and is responsible for a few large recalls. Although these These strains generally do not produce flavors that are considered unpleasant (although . For example, acetaldehyde and sulfur dioxide are produced in very low amounts compared to other brewing strains. However, all ''diastaticus'' strains tested in one study produced phenols , with most being above flavor threshold. Most strains also produced significant amounts of isoamyl acetate (banana ester) and other fruity esters, making them taste very similar to German wheat strains. A small number of strains also produce above flavor threshold levels of diacetyl <ref name="Meier-Dörnberg_2018">[https://www.ncbi.nlm.nih.gov/pubmed/29518233 Saccharomyces cerevisiae variety diastaticus friend or foe? Spoilage potential and brewing ability of different Saccharomyces cerevisiae variety diastaticus yeast isolates by genetic, phenotypic and physiological characterization. Meier-Dörnberg T, Kory OI, Jacob F, Michel M, Hutzler M. 2018. doi: 10.1093/femsyr/foy023.]</ref>), it . This variant is often viewed as a contaminant because of its ability to over-attenuate. A survey of contamination reports in the last ten years at European breweries (50% of which were German breweries, which are obligated by law to report such contaminations) found an increase in reports from 2015, 2016, and 2017. 71% of the contamination incidents originated from the packaging systems (bottling/canning lines). These contaminations were tracked down to the filler environment and/or biofilms in the pipework system of the filler which stemmed from hygienic problems. As such, sometimes contaminations can be sporadic with some bottles being contaminated while others are not. The other 29% of the contaminations were tracked down to primary contaminations in the brewhouse, fermentation cellar, and storage cellar <ref name="Meier-Dörnberg">[https://www.mbaa.com/publications/tq/tqPastIssues/2017/Pages/TQ-54-4-1130-01.aspx Incidence of Saccharomyces cerevisiae var. diastaticus in the Beverage Industry: Cases of Contamination, 2008–2017. Tim Meier-Dörnberg, Fritz Jacob, Maximilian Michel, and Mathias Hutzler. 2017. MBAA Technical Quarterly; http://dx.doi.org/10.1094/TQ-54-4-1130-01.]</ref>.

This variant of ''S. cerevisiae'' can produce extracellular glucoamylase (also called [https://en.wikipedia.org/wiki/Alpha-glucosidase alpha-glucosidase], which is the same enzyme that ''[[Brettanomyces]]'' produces to break down starches and dextrins). This enzyme is released outside of the cell and can break down the α-1,4 linkages of starches and dextrins releasing glucose that is then fermented by the yeast. The capability to produce this enzyme is encoded by the STA1, STA2, or STA3 genes. Not all strains containing one of these genes produces the glucoamylase enzyme, or are as effective as others at metabolizing dextrins <ref>[https://link.springer.com/article/10.1007%2FBF00365634 STA10: A gene involved in the control of starch utilization by Saccharomyces. Julio Polaina, Melanie Y. Wiggs. 1983.]]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/yea.1102/full Structural analysis of glucoamylase encoded by the STA1 gene of Saccharomyces cerevisiae (var. diastaticus). Ana Cristina Adam, Lorena Latorre-Garcia, Julio Polaina. 2004.]</ref>. It has been reported by some microbiologists that most brewing strains that contain STA1, STA2, or STA3 do produce the glucoamylase enzyme <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1935201836508021/?comment_id=1936604203034451&reply_comment_id=1937166892978182&comment_tracking=%7B%22tn%22%3A%22R7%22%7D Richard Preiss. Milk the Funk thread about STA1 gene correlation to glucoamylase production. 12/31/2017.]</ref><ref name="mbaa_diastaticus">[http://masterbrewerspodcast.com/068-diastaticus-part-1 Matthew Peetz of Inland Island and Tobias Fischborn of Lallemand. "Master Brewers Association Podcast" 12/25/2017.]</ref>(~16 mins). A study that surveyed 18 strains of ''diastaticus'' that contain the STA gene found that only one was not able to ferment dextrins <ref name="Meier-Dörnberg_2018" />. Richard Preiss has also reported that WLP351 has the STA gene, but is not able to ferment dextrins <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1888017211226484/?comment_id=2013050695389801&reply_comment_id=2013355312026006&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Richard Preiss. Milk The Funk Facebook group thread on diastaticus strains that do not ferment dextrins. March 2018.]</ref>. When beer containing this yeast is packaged too early, it will continue to slowly ferment dextrins and cause over-carbonation. When pitching a proper cell count or pitching rate of a ''diastaticus'' yeast strain into the wort, it some strains will fully ferment as quickly or nearly as quickly as any other brewers yeast, while other strains may take as long as 16 days to fully ferment a simple 12. ''S4°P (1. cerevisiae'' var ''diastaticus'' can grow at 37°C and can also remain viable at refrigeration temperatures <ref>[http://www.ebc2017.com/inhalt/uploads/P095_Begrow.pdf Wade Begrow050 SG) wort. "Recent notable microbiological contaminations of craft beer in the United States". Presentation poster at EBC 2017. Retrieved 11/19/2017.]</ref>. These strains are effectively eliminated by standard cleaning and sanitation practices, although inadequate cleaning hygiene can lead A highly dextrinous wort may take longer to biofilm formation which makes them more resistant to cleaning regiments <ref name="Meier-Dörnberg" />fully ferment. The problem of slow fermentation in already packaged beer is usually only a concern when ''diastaticus'' is introduced as a very small cell count, for example as an accidental contamination <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1982499288444942/?comment_id=1983013578393513&comment_tracking=%7B%22tn%22%3A%22R1%22%7D Caroline Whalen Taggart. Milk The Facebook post on how quickly diastaticus ferments. 02/09/2018.]</ref>. The enzyme produced by these strains is heat stable and can continue to work on starches and dextrins even after the yeast is killed by heat pasteurization <ref>[https://www.mbaa.com/publications/tq/tqPastIssues/1983/Abstracts/tq83ab19.htm Factors That Control the Utilization Of Wort Carbohydrates by Yeast. G. G. Stewart, I. Russell, and A. M. Sills. MBAA Technical Quarterly, Vol. 20, No. 1, 1983.] </ref>. Almost all strains of ''S. cerevisiae'' var. ''diastaticus'' are able to ulilize all of the sugars found in wort (e.g. glucose, fructose, sucrose, maltose, maltotriose), although one strain tested in a recent study could not efficiently ferment maltose or maltotriose <ref name="Meier-Dörnberg_2018" />. ''S. cerevisiae'' var ''diastaticus'' can grow at 37°C and can also remain viable at refrigeration temperatures <ref>[http://www.ebc2017.com/inhalt/uploads/P095_Begrow.pdf Wade Begrow. "Recent notable microbiological contaminations of craft beer in the United States". Presentation poster at EBC 2017. Retrieved 11/19/2017.]</ref>. Some strains of ''diastaticus'' are as flocculant as typical ale strains, while others are less flocculant <ref name="Meier-Dörnberg_2018" />. One strain of ''diastaticus'', the Belle Saison strain from Lallemand, is killer neutral, which means that killer wine strains will not kill it (it is not verified if Belle Saison is the same as WY3711/Thiriez, although it is suspected to be). Other strains of ''diastaticus'' may or may not be killer neutral (more data is needed; see [[Saccharomyces#Killer_Wine_Yeast|killer wine strains]] for more information on this topic).

Var. ''diastaticus'' contamination in breweries has been a recent hot topic. These strains are effectively eliminated by standard cleaning and sanitation practices, and the although inadequate cleaning hygiene can lead to biofilm formation which makes them more resistant to cleaning regiments <ref name="Meier-Dörnberg" />. The source of some contaminations has also been suspected to potentially come from certain yeast suppliers (namely White Labs) <ref>[https://www.courthousenews.com/wp-content/uploads/2017/11/Left-Hand-v-White-Labs-COMPLAINT.pdf District Court, Boulder County, Colorado. Case Number 2017CV31132. Filed 11/14/2017.]</ref>. Detection of ''S. cerevisiae'' var. ''diastaticus'' as a contaminant can be difficult. Contamination usually occurs as a secondary contaminant (meaning in the packaging system), and can come from contact with beer lines, by air circulation in the area of the packaging equipment, or by insufficient heat treatment of the packaging line. Since a very small number of cells is enough to contaminate beer, contaminations can be sporadic with only a percentage of bottles being contaminated <ref name="Meier-Dörnberg_2018" />. Documented attenuation percentages above 75% for any strain of ''S. cerevisiae'' is also an indicator that the strain could be ''diastaticus'', however, some non-diastaticus strains can also attenuate higher than 75%, so this indicator is not a reliable method to be sure that a given strain is ''diastaticus'' <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2004689559559248/?comment_id=2004695002892037&reply_comment_id=2005133672848170&comment_tracking=%7B%22tn%22%3A%22R1%22%7D Adi Hastings. Milk The Funk Facebook Group post on non-diastaticus strains with high attenuation. 02/27/2018.]</ref><ref name="mbaa_diastaticus" />. Often this contamination can only be detected by sensory testing weeks after packaging. This yeast has reportedly been detected using [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1981.tb04005.x/pdf LCSM agar plates], although other species of wild ''Saccharomyces'' yeast can grow on this media <ref name="mbaa_diastaticus" />(~18 mins) and PCR DNA analysis is required to give a positive identification of ''diastaticus''. 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 ''diastaticus'' 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" />.

WY3711 saison yeast, which originated from Basserie Thiriez, has been determined to be this subspecies ''S. cerevisiae'' var. ''diastaticus'' <ref name="preiss_diastaticus" />. Since yeast cannot be patented, many yeast labs are thought to offer this strain to customers. In the [[Saccharomyces#Commercial_Farmhouse.2FBelgian_Strains_of_Saccharomyces|commercial culture]] lists below where we believe a lab is selling this strain of yeast or might be selling this another strain of ''diastaticus'' yeast, we note that it is determined/or suspected to be ''diastaticus''. The Belle Saison strain from Lallemand is killer neutral, which means that killer wine strains will not kill it (it is not verified if Belle Saison is the same as WY3711/Thiriez, although it is suspected to be).

White Labs now reports that the strains [https://whitelabs.com/yeast-bank/wlp590-french-saison-ale-yeast WLP590], [https://www.whitelabs.com/yeast-bank/wlp099-super-high-gravity-ale-yeast WLP099], [https://www.whitelabs.com/yeast-bank/wlp045-scotch-whisky-yeast WLP045], [https://www.whitelabs.com/yeast-bank/wlp570-belgian-golden-ale-yeast WLP570], and [https://www.whitelabs.com/yeast-bank/wlp644-saccharomyces-bruxellensis-trois WLP644] are ''diastaticus''. Some hints as to which other White Labs products might also be ''diastaticus'' have been deduced from the [[Saccharomyces#History_of_Domestication|Gallone et al. study that ]] which published DNA sequencing on most of the yeast strains in the White Labs bank. However, the codes used in the Gallone paper for each strain of yeast were not defined as far as which White Labs products they correspond to which code used in the study. Some of the codes have been speculated on which White Labs strains they might refer to (see [[Saccharomyces#History_of_Domestication|History of Domestication]] above). The strains from the Gallone paper that appear to contain STA1 are Beer002, Wine019, Beer092 and Beer059. The Beer059 code might correspond to WLP026 according to this speculative [https://www.facebook.com/groups/MilkTheFunk/permalink/1400297539998456/?comment_id=1908170505877821&comment_tracking=%7B%22tn%22%3A%22R0%22%7D table], which has had reports of high attenuation. It is not clear at this time whether this strain is ''diastaticus'' or not <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1400297539998456/?comment_id=1909596632401875&reply_comment_id=1910328215662050&comment_tracking=%7B%22tn%22%3A%22R9%22%7D MTF thread on STA1 gene and White Labs strains that might have it or not. Milk The Funk Facebook group. 12/07/2017.]</ref>. There has been a report by Richard Preiss of [[Escarpment Laboratories]] that WLP570 and [https://www.whitelabs.com/yeast-bank/wlp585-belgian-saison-iii-ale-yeast WLP585] both have the STA1 gene, but it takes weeks before they hyper-attenuate <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1888017211226484/?comment_id=1911782002183338&reply_comment_id=1982274298467441&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Richard Preiss. Milk The Funk Facebook group post on WLP570 and WLP585 being diastaticus. 02/08/2018.]</ref>. Other yeast labs such as [http://www.lallemand.com/ Lallemand], [https://inlandislandyeast.com/yeast-library/inis-491-saison-french/ Inland Island], [https://www.escarpmentlabs.com/strains Escarpment Labs], and [https://www.theyeastbay.com The Yeast Bay] also list which strains they offer are ''diastaticus''.