Changes

Aglycones can be released from glycosides via a low pH. Generally, this occurs at lower pH'sand Daenen et al. (2007) attributed most of the breakdown of glycosides to beta-glucosidase enzymes <ref name="Daenen2" />, but different types of glycosides are more readily broken down at different pH's. For example, ocimenols (lemon, lime <ref>[http://www.thegoodscentscompany.com/data/rw1020581.html "Ocimenol". The Good Scents Company. Retrieved 06/26/2017.]</ref>) are formed from glycoside breakdown at a pH of 1, but terpenes such as linalool, nerol, and geraniol (commonly found in hops and other plant material) are formed at a pH of 3, and alpha-terpineol was formed at both pH values. The acidic breakdown of these glycosides were found to contribute to the flavor of wine during aging <ref name="Maicas"></ref>. Daenen et al. (2007) also found that acidic hydrolysis was responsible for the formation of alpha-ionol, beta-damascenone, linalool and alpha-terpineol and to a lesser extent benzyl alcohol <ref name="Daenen2" />.

In beer, it was found that the lower the pH of the beer the higher the amount of the ketone damascenone (floral, rose <ref>[https://en.wikipedia.org/wiki/Damascenone "Damascenone". Wikipedia. Retrieved 06/26/2017.]</ref>) and dimethyl trisulfide (sulfury cooked onion <ref>[http://www.thegoodscentscompany.com/data/rw1008101.html "Dimethyl trisulfide". The Good Scents Company. Retrieved 06/26/2017.]</ref>). In one study, at a pH of 3, beta-damascenone was reported to be ~27 ppb and dimethyl trisulfide was reported to be 650 ppt. At a pH of 4.2, they were 17 ppb and 300 ppt respectively. At a ph of 5, beta-damascenone was around 12 ppb and dimethyl trisulfide 50 ppt. This was believed to be due to the acidic hydrolysis of glycosides, and it was speculated that other glycosides could have a flavor impact on beers that contain fruit or herbs due to acidic hydrolysis of glycosides <ref>How Low pH Can Intensify ?-Damascenone and Dimethyl Trisulfide Production through Beer Aging. LAURENCE GIJS, FABIENNE CHEVANCE, VESNA JERKOVIC, AND SONIA COLLIN. 2002. DOI: 10.1021/jf020563p.</ref>.

One study screened the beta-glucosidase activity of several strains of ''Saccharomyces cerevisiae'', ''Saccharomyces pastorianus'', and ''Brettanomyces'' spp <ref name="Daenen1">[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03566.x/full Screening and evaluation of Daenen et al. (2007)] screened the glucoside hydrolase beta-glucosidase activity in of several strains of ''Saccharomyces cerevisiae'', ''Saccharomyces pastorianus'', and several ''Brettanomyces brewing yeasts. L. Daenen, D. Saison, F. Sterckx, F.R. Delvaux, H. Verachtert, G. Derdelinckx. 2007.]</ref>'' species. None of the lager brewing strains showed beta-glucosidase activity. Out of 32 strains of ''S. cerevisiae'', only one strain (a wine strain called "U228") showed beta-glucosidase activity, however its activity was repressed in the presence of glucose. This indicates that most ''S. cerevisiae'' strains do not have the capability of producing beta-glucosidase, but it is possible that some very few strains can <ref name="Daenen1">[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03566.x/full Screening and evaluation of the glucoside hydrolase activity in Saccharomyces and Brettanomyces brewing yeasts. L. Daenen, D. Saison, F. Sterckx, F.R. Delvaux, H. Verachtert, G. Derdelinckx. 2007.]</ref>. HoweverAdditionally, beta-glucosidase activity for ''S. cerevisiae'' is can be inhibited by the pH levels of found in wine and sour beer (optimal at pH 5) <ref name="Mansfield"></ref>. All strains of ''S. cerevisiae'' did release another enzyme called beta-glucanase, which led to varying degrees of breaking down some smaller glycosides found in hops (hop extract was tested, not whole hops) containing the aglycones methyl salicylate, 1-octen-3-ol, and cis-3-hexen-1-ol, but not linalool (another study by [http://onlinelibrary.wiley.com/doi/10.1002/jib.418/abstract Sharp et al.] found that both ale and lager yeasts exhibit a wide range of beta-glucosidase activity, but the results should be repeated using a different substrate because the substrate that was used could have been broken down by beta-glucanase enzyme instead of beta-glucosidase <ref name="Sharp_2017">[http://onlinelibrary.wiley.com/doi/10.1002/jib.418/abstract The effect of hopping regime, cultivar and β-glucosidase activity on monoterpene alcohol concentrations in wort and beer. Daniel C. Sharp, Jan Steensels, Thomas H. Shellhammer. 2017.]</ref>). None of the ''B. bruxellensis'' strains showed this activity, but the researchers only tested strain of ''B. custersianus'' and both of the ''B. anomala'' strains tested did show cell-associated (intracellular) beta-glucosidase activity. In particular, the ''B. custersianus'' strain was tested against glycosides from hops, in which case high amounts of the aglycones linalool (citrus, orange, lemon, floral <ref>[http://www.thegoodscentscompany.com/data/rw1007872.html "Linalool." The Good Scents Company. Retrieved 05/12/2016.]</ref>), methyl salicylate (minty, wintergreen <ref>[http://www.rsc.org/chemistryworld/2015/09/methyl-salicylate-oil-wintergreen-podcast "Methyl salicylate." Chemistry World. Retrieved 05/12/2016.]</ref>), 1-octen-3-ol (mushroom, earthy <ref>[http://www.thegoodscentscompany.com/data/rw1024051.html "1-octen-3-ol." The Good Scents Company. Retrieved 05/12/2016.]</ref>) and cis-3-hexen-1-ol (grassy, melon rind <ref>[http://www.thegoodscentscompany.com/data/rw1005932.html "(Z)-3-hexen-1-ol." The Good Scents Company. Retrieved 05/12/2016.]</ref>) were released from hop extracts <ref name="Daenen1"></ref>. The beta-glucosidase activity was elevated when co-fermenting ''B. custersianus'' with ''S. cerevisiae''. The authors also found dihydroedulan 1 and 2 (elderberry aroma) and theaspirane A and B (woody and campfire aromas), which are classified as norisoprenoids, were released from dry hopping <ref>[http://www.asbcnet.org/events/archives/Documents/2008WBCprogbook.pdf World Brewing Congress, 2008. Pg 80. Retrieved 05/13/2016.]</ref>. ''B. custersianus'' has been isolated from the later stages of lambic fermentation, and it is thought that its ability to produce beta-glucosidase, which gives it the ability to ferment cellobiose and cellotriose, is a possible adaptation from living in oak barrels <ref name="Daenen1"></ref>. Recent studies on hops have linked an increase in fruity thiols from hops (3-mercaptohexan-1-ol and 4-mercapto-4-methylpentan-2-one) being produced during fermentationfrom the production of beta-lyase enzyme, and this could also explain anecdotal reports of increased fruity aromas from exposing hops to fermentation (it is unknown what exactly causes the increase in see [http://scottjanish.com/genetically-modified-gm-yeast-strains-unlocking-bound-hop-thiols during -and-engineering-targeted-fermentation-characteristics/ this article by Scott Janish] on beta-lyase enzymes in GM and non-GM yeast strains) . <ref>Private correspondence with Richard Preiss by Dan Pixley. 05/16/2016.</ref><ref>[https://beerandbrewing.com/VuhJRCUAAHMUNfil/article/hops-oils--aroma-uncharted-waters "Hops Oils & Aroma: Uncharted Waters," by Stan Hieronymus. Beer & Brewing. 03/16/2016. Retrieved 05/16/2016.]</ref>.  [https://www.academia.edu/23874347/Properties_of_endogenous_%CE%B2_glucosidase_of_a_Saccharomyces_cerevisiae_strain_isolated_from_Sicilian_musts_and_wines Palmeri et al. (2002)] reported one wine strain out of 80 strains of ''S. cerevisiae'' found in Sicilian must that had high beta-glucosidase activity and is active during wine fermentation conditions <ref>[https://www.academia.edu/23874347/Properties_of_endogenous_%CE%B2_glucosidase_of_a_Saccharomyces_cerevisiae_strain_isolated_from_Sicilian_musts_and_wines Spagna, G., Barbagallo, R. N., Palmeri, R., Restuccia, C., & Giudici, P. (2002). Properties of endogenous β-glucosidase of a Saccharomyces cerevisiae strain isolated from Sicilian musts and wines. Enzyme and Microbial Technology, 31(7), 1030–1035. https://doi.org/10.1016/S0141-0229(02)00233-8]</ref>. Another study by [http://onlinelibrary.wiley.com/doi/10.1002/jib.418/abstract Sharp et al.] found that both ale and lager yeasts exhibit a wide range of beta-glucosidase activity, but the results should be repeated using a different substrate because the substrate that was used could have been broken down by beta-glucanase enzyme instead of beta-glucosidase <ref name="Sharp_2017">[http://onlinelibrary.wiley.com/doi/10.1002/jib.418/abstract The effect of hopping regime, cultivar and β-glucosidase activity on monoterpene alcohol concentrations in wort and beer. Daniel C. Sharp, Jan Steensels, Thomas H. Shellhammer. 2017.]</ref>Additionally, Lallemand claims that three brewing strains that they offer produce beta-glucosidase enzymes that can promote hop biotransformation, but the details of this activity have not been published to our knowledge (BRY-97, New England, and Belle Saison) <ref>[http://masterbrewerspodcast.com/119-biotransformation Eric Abbot. Master Brewers Association podcast, episode 119. 02/04/2019.]</ref> (~8:50 min in).

The same strain of ''B. custersianus'' was screened for beta-glucosidase activity and aglycone byproducts during the refermentation of sour cherries in beer (a very small amount of the byproducts were manufactured by the yeast ''de novo'', particularly linalool, alpha-terpineol, alpha-ionol, and a precursor that leads to beta-damascenone under low pH conditions). Different portions of the cherries were tested: whole cherries with stones (pits), cherry pulp without stones, cherry juice without stones or other solids from the fruit, and the stones alone. Benzaldehyde (almond, cherry stone flavor) was produced during fermentation in all cases, and reduced to benzyl alcohol (almond flavor) and benzyl acetate (fruity, jasmine flavor) by the end of fermentation. There were higher levels of these benzyl based compounds in the whole cherries and cherry stone alone samples, indicating that cherry stones make a big impact on the almond flavors found in cherry sour beers. Methyl salicylate, linalool, alpha-terpineol (pine), geraniol (rose, lime, floral) and alpha-ionol (floral, violet), eugenol (spicy, clove, medicinal) and isoeugenol (fine delicate clove) levels increased in all forms of cherries added except for stones alone, indicating that these aglycones are more present in the flesh and juice of the cherries <ref name="Daenen2"></ref>. Another study that performed whole genome sequencing on a strain of ''B. naardenensis'' found that it had two genes that could potentially allow this species to produce beta-glucosidase, but this was not confirmed in the study <ref>[https://www.mdpi.com/2076-2607/7/11/489 Assembly and Analysis of the Genome Sequence of the Yeast Brettanomyces naardenensis CBS 7540. Ievgeniia A. Tiukova, Huifeng Jiang, Jacques Dainat, Marc P. Hoeppner, Henrik Lantz, Jure Piskur, Mats Sandgren, Jens Nielsen, Zhenglong Gu, and Volkmar Passoth. 2019. DOI: https://doi.org/10.3390/microorganisms7110489.]</ref>.

The effects of beta-glucosidase on hops may be limited even in ideal conditions using pure beta-glucosidase that is highly efficient in beer where beta-glucosidase activity by yeast is suppressedlimited. Sharp et al. (2017) determined that hops contain such a small amount of glycosides that their release doesn't contribute much to hop flavor and aroma. While previous studies focused on hop extracts, they studied glycosides in whole leaf hops for the first time and found non-significant levels of hop-derived monoterpenes from glycosides even when using pure beta-glucosidase extracted from almonds. For example, linalool was increased by 16.5 μg/L when using the highest hopping rate, but this amount has little impact on the overall aroma and flavor of the beer. TerineolTerpineol, citronellol, nerol, and geraniol were also not increased in significant amounts, however 1-octanol (waxy, green, citrus, orange, aldehydic, fruity <ref>[http://www.thegoodscentscompany.com/data/rw1021071.html Octanol. The Good Scents Company. Retrieved 03/31/2017.]</ref>) was increased significantly <ref name="Sharp_2017" />. In 2020, whole genome sequencing and glycosidic activity were tested for 84 strains of ''Brettanomyces'' by [https://www.frontiersin.org/articles/10.3389/fmicb.2020.00637/full Colomer et al]. They found that the capability of ''Brettanomyces'' to break down glycosides is determined by possessing two genes: ''BbBGL1'' and ''BbBGL2''. The genes called ''BbBGL2'' have a major role in whether glycosides are broken down, while the role of ''BbBGL1'' is minimal. About half of the strains had some level of glycosidic activity, although the majority was low with a couple of strains that had high levels of glycosidic activity, thus these genes alone do not account for the wide variation in glycosidic activity levels in ''Brettanomyces'' (see [https://www.frontiersin.org/files/Articles/495404/fmicb-11-00637-HTML-r1/image_m/fmicb-11-00637-g007.jpg this figure] from the study which maps beta-glucosidase activity for the 84 strains that were sequenced) <ref>[https://www.frontiersin.org/articles/10.3389/fmicb.2020.00637/full Assessing Population Diversity of Brettanomyces Yeast Species and Identification of Strains for Brewing Applications. Marc Serra Colomer, Anna Chailyan, Ross T. Fennessy, Kim Friis Olsson, Lea Johnsen, Natalia Solodovnikova and Jochen Forster. 2020. DOI: https://doi.org/10.3389/fmicb.2020.00637.]</ref>. The beta-glucidase levels were also measured for 5 strains (4 strains of ''B. bruxellensis'' and 1 strain of ''B. anomalus'') that have the genetic make up to produce this enzyme; most of the enzyme was only produced within the cell (intracellular) for all of the strains tested, and only small amounts were produced outside of the cells except for one strain of ''B. anomalus''. The enzyme therefore wouldn't act on glycosides outside of the cell unless the cell ruptured. There was also a small amount of beta-glucosidase activity within the cell wall of one of the strains of ''B. anomalus''. They also fermented a dry hopped beer with these strains and found that the strains with the lowest beta-glucosidase activity had the lowest conversion of geraniol to β‐citronellol, and therefore there was no correlation between beta-glucosidase activity and hop biotransformation (although there was evidence of another unidentified type of biotransformation occurring with the hops (see [[Brettanomyces#Hop_Biotransformation|''Brettanomyces'' hop biotransformation]]) <ref>[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.610 Biotransformation of hop derived compounds by Brettanomyces yeast strains. Marc Serra Colomer, Birgitte Funch, Natalia Solodovnikova, Timothy John Hobley, Jochen Förster. 2020. DOI: https://doi.org/10.1002/jib.610.]</ref>.

See also :* [[Hops#Glycosides|Glycosides in Hops]].* [http://scottjanish.com/genetically-modified-gm-yeast-strains-unlocking-bound-hop-thiols-and-engineering-targeted-fermentation-characteristics/ "Genetically Modified (GM) Yeast Strains: Unlocking Bound Hop Thiols and Engineering Targeted Fermentation Characteristics," by Scott Janish.] ===Activity of Other Yeasts===A strain of ''Candida glabrata'' was selected in a study for its high beta-glucosidase activity, its tolerance to ethanol, and its ability to utilize maltose, and was shown to produce novel flavor characteristics in beer fermentation, including a significant increase in geraniol <ref>[https://www.sciencedirect.com/science/article/abs/pii/S0308814622026887#f0020 Application of non-Saccharomyces yeasts with high β-glucosidase activity to enhance terpene-related floral flavor in craft beer. Xiaoyu Han, Qiuxing Qin, Chenyu Li, Xiaoxuan Zhao, Fangxu Song, Mengjiao An, Ying Chen, Xiuqin Wang, Weidong Huang, Jicheng Zhan, Yilin You. 2022.]</ref>. Strains of ''Meyerozyma guilliermondii'' and ''Hanseniaspora uvarum'' that were isolated from a spontaneous wine fermentation have also been found to have positive results when co-fermented with ''S. cerevisiae'' in wine. Specifically, compared to the control wines, there were higher levels of the terpenes: isopulegol, citronellol, geranylacetone, geraniol, trans-nerolidol, and nerol. This was associated with the high beta-glucosidase activity of these yeast strains <ref>[https://www.frontiersin.org/articles/10.3389/fmicb.2022.845837/full Indigenous Non-Saccharomyces Yeasts With β-Glucosidase Activity in Sequential Fermentation With Saccharomyces cerevisiae: A Strategy to Improve the Volatile Composition and Sensory Characteristics of Wines. Gao Pingping, Peng Shuai, Sam Faisal Eudes, Zhu Yatong, Liang Lihong, Li Min, Wang Jing. 2022.]</ref>.

All plants contain at least tiny amounts of [https://en.wikipedia.org/wiki/Hydrogen_cyanide hydrogen cyanide] ('''HCN'''), however, some plants also release high amounts of HCN from a class of glycosides called "cyanogenic glycosides", also called "cyanoglycosides". [https://en.wikipedia.org/wiki/Amygdalin Amygdalin] and [https://en.wikipedia.org/wiki/Linamarin linamarin] are common examples of cyanogenic glycosides <ref name="Gleadow_2014"></ref>. Amygdalin is often sometimes marketed as a cure for cancer by the health food industry, but this claim is not supported by clinical data, and digestion of too much amygdalin can be dangerous <ref>[https://www.quackwatch.org/01QuackeryRelatedTopics/Cancer/laetrile.html Wilson, Benjamin. "The Rise and Fall of Laetrile". Quackwatch.org website. 01/07/2017. retrieved 03/30/2017.]</ref><ref>[http://www.nejm.org/doi/pdf/10.1056/NEJM198201283060403 A Clinical Trial of Amygdalin (Laetrile) in the Treatment of Human Cancer. Charles G. Moertel, M.D., Thomas R. Fleming, Ph.D., Joseph Rubin, M.D., Larry K. Kvols, M.D., Gregory Sarna, M.D., Robert Koch, M.D., Violante E. Currie, M.D., Charles W. Young, M.D., Stephen E. Jones, M.D., and J. Paul Davignon, Ph.D. 1982. DOI: 10.1056/NEJM198201283060403.]</ref><ref>[https://www.infona.pl/resource/bwmeta1.element.springer-2c7e4ea1-3683-3bbd-9394-a98a551e7c63 Laetrile for cancer: a systematic review of the clinical evidence. Stefania Milazzo, Stephane Lejeune, Edzard Ernst. 2007. DOI: 10.1007/s00520-006-0168-9.]</ref><ref>[http://www.sciencedirect.com/science/article/pii/S0944711316000362 Amygdalin, quackery or cure? Roman A. Blahetaa, Karen Nelsonb, Axel Haferkampa, Eva Juengela. 2016.]</ref>. HCN is released from cyanogenic glycosides just like other types of glycosides: beta-glucosidase enzyme or exposure to low pH breaks the bond between a glucose molecule and an unstable compound called "cyanohydrin" (or "alpha-hydroxynnitrile"), which then disassociates into a ketone or benzaldehyde and an HCN molecule. In cyanogenic glycosides, this reaction is called "cyanogenesis". Cyanogenesis is stimulated by maceration, and by bacteria in the human gut <ref name="Speijers">[http://www.inchem.org/documents/jecfa/jecmono/v30je18.htm "Cyanogenic Glycosides", First Draft. Dr G. Speijers. National Institute of Public Health and Environmental Protection Laboratory for Toxicology, Bilthoven, The Netherlands. Retrieved 08/25/2016.]</ref>. Although the optimum pH of cyanogenesis (at least for amygdalin) is 5.0 - 5.8, cyongenesis can occur at a wide range of pH values, and can occur in the presence of acid <ref>[http://www.sciencedirect.com/science/article/pii/S0308814601003132 Total cyanide determination of plants and foods using the picrate and acid hydrolysis methods. M Rezaul Haque, J Howard Bradbury. 2002.]</ref>. If seeds containing cyanogenic glycosides are ground up, the coarseness to which they are ground effects how quickly cyanogenesis occurs. Finely ground seeds extract HCN within an hour, where as coarsely ground seeds extract within 24 hours <ref name="tuncel">[http://www.sciencedirect.com/science/article/pii/030881469599841M The effects of grinding, soaking and cooking on the degradation of amygdalin of bitter apricot seeds. G Tunçel, M.J.R Nout, L Brimer. 1995.]</ref>. HCN boils at a relatively low temperature (25.6°C / 78.1°F) <ref name="Gleadow_2014"></ref>. In some cases, soaking, cooking, and/or sometimes fermenting foods with certain bacteria or yeast (this has not been fully documented with ''Saccharomyces'' or ''Brettanomyces'') that contain cyanogenic glycosides allows the HCN to be released, and then subsequent cooking afterwards will boil off the cyanide <ref>[http://www.sciencedirect.com/science/article/pii/016816059400115M International Journal of Food Microbiology. M.J.R. Nout, G. Tunçe, L. Brimer. 1995.]</ref><ref name="Chaouali"></ref>.

Upon learning about cyanogenic glycosides, brewers often question the toxicity of ingredients such as cherry pits or apricot kernels in beer. Cherry pits have traditionally been used in [[lambic]] kriek beers in Belgium. However, the dilution of HCN from cherry pits in beer results in benign levels. Assuming full breakdown of these glycosides, and that none of the HCN boils off (25.6°C boiling temperature), levels of HCN introduced from cherry pits are too low to cause harm to adult humans. The EU regulates that alcoholic beverages cannot exceed 1 mg of HCN per ABV percentage (v/v%) per liter <ref>[http://ec.europa.eu/food/fs/sfp/addit_flavor/flav09_en.pdf COUNCIL DIRECTIVE of 22 June 1988 on the approximation of the laws of the Member States relating to flavourings for use in foodstuffs and to source materials for their production (88/388/EEC). The European Food Commission, Food Safety. Retrieved 08/26/2016.]</ref>. Luk Daenen, a glycoside researcher, calculated that for a 4% ABV alcohol beer, 4 mg of HCN per liter is allowed. With 200 grams of cherries per liter, and the pits being 10 - 14 grams of that weight, there is 22 - 30.8 mg amygdalin per liter of beer. Around 6% of the weight of amygdalin is converted into HCN. Assuming maximum extraction of HCN from the amygdalin glycoside, which is unlikely because the pits are not ground up when used in beer, this equates to 1.3 - 1.82 mg of HCN per liter of beer. This amount is less than the 4 mg of HCN per liter that the EU regulation states. Considering that ~42 mg of HCN is required to kill a person that weighs 70 kilograms (154 pounds), that person would need to drink around 23 liters of beer <ref name="daenen">[https://www.uclouvain.be/cps/ucl/doc/inbr/documents/presentation-luk-daenen.pdf "Use of beta-glucosidase activity for flavour enhancement in specialty beers," slideshow by Luk Daenen. 2012. Retrieved 08/26/2016.]</ref>. Considering that 350 mL of pure alcohol would kill a 70 kilogram adult <ref>[http://www.alcohol.org.nz/alcohol-its-effects/health-effects/alcohol-poisoning "Alcohol Poisoning". NZ Health Promotion Agency. Retrieved 08/26/2016.]</ref>, the amount of 4% ABV beer required to kill a 70 kg adult from alcohol poisoning is around 8.75 liters. Alcohol would kill such a person far before cyanide poisoning would become a concern. In general, the potential cyanide in most plants will become too dilute to have any health problems when added to beer in normal amounts, however there might still be plants that are extremely high in HCN content that should be avoided in beer (see the table below). If there is a concern that an ingredient containing potentially high levels of HCN could reach unhealthy levels in beer, the beer should be sent for lab analysis so that the HCN levels can be determined before being consumed.

| Elderflower (leaves/stems) || 1600 <ref name="nordicfoodlab">[https://web.archive.org/web/20190812014649/http://nordicfoodlab.org:80/blog/2013/10/elder-a-love-story "Elder – a love story". Justine de Valicourt. Nordic Food Lab. 10/03/2013. Retrieved 09/07/2016.]</ref> || Sambunigrin (or sometimes prunasin, holocalin, or zierin) <ref name="elderflowers">[https://www.researchgate.net/publication/233262135_Cyanogenic_Glycosides_from_Sambucus_Nigra Cyanogenic Glycosides from Sambucus Nigra. Marina Dellagreca, Antonio Fiorentino, Pietro Monaco, Lucio Previtera & Ana M. Simonet. 2006.]</ref>