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Aglycones have been identified in many fruits and herbs such as grapes, apricots, peaches, yellow plums, quince, sour cherry, passion fruit, kiwi, papaya, pineapple, mango, lulo, raspberry, strawberry, and tea <ref name="Maicas">[http://www.ncbi.nlm.nih.gov/pubmed/15635463 "Hydrolysis of terpenyl glycosides in grape juice and other fruit juices: a review." Sergi Maicas, José Juan Mateo. May 2005.]</ref><ref name="Winterhalter"></ref>. They have been found in different parts of plants, including the green leafy parts, fruit, roots, rhizomes, petals, and seeds. Aglycones in plants are highly complex structures and very diverse, and their percentages can vary from crop to crop. In plants, these include alcohol type aglycones such as terpenols, terpenes, linalool oxides, as well as other flavor precursors including various alcohols, norisoprenoids, phenolic acids and probably volatile phenols such as vanillin <ref name="Maicas"></ref>. In fruits, there are mostly just 4 types of flavonol type aglycones: [https://en.wikipedia.org/wiki/Quercetin quercetin] (found in nearly all fruits), [https://en.wikipedia.org/wiki/Kaempferol kaempherol] (found in 80% of fruit), and less commonly [https://en.wikipedia.org/wiki/Quercetin quercetin] and [https://en.wikipedia.org/wiki/Isorhamnetin isorhamnetin] <ref>[https://books.google.com/books?id=vHqke7F4lWYC&pg=PA59&lpg=PA59&dq=aglycones+in+fruit&source=bl&ots=7Gb10SPZk7&sig=6gaZlwpVaHuteoiVP68zvt6HcpE&hl=en&sa=X&ved=0ahUKEwjk0qW9wp3NAhUCKZQKHfUzDrQQ6AEIKTAC#v=onepage&q=aglycones%20in%20fruit&f=false Fruit Phenolics. Jean-Jacques Macheix, Annie Fleuriet. CRC Press, Mar 20, 1990. Pgs 57-61.]</ref> (see [http://nutrition.ucdavis.edu/content/infosheets/fact-pro-flavonol.pdf this UC Davis PDF] for amounts in different fruit and potential health benefits as antioxidants). In many cases of fruit, the amount of aromatic aglycones that are bound up in glycosides outnumber the amount that are free in a ratio of 2:1 to 8:1 <ref name="Maicas"></ref>. Aglycones that are bound up in glycosides tend to be more water soluble and less reactive once unbound than the naturally free version. By providing enzymes that break the glycosidic bond, discarded parts of plants (peels, stems, skins, etc.) have been used to produce natural flavorings from the remaining and abundant glycosides <ref name="Winterhalter">[http://link.springer.com/chapter/10.1007%2FBFb0102063 "Glycoconjugated aroma compounds: Occurrence, role and biotechnological transformation." Peter Winterhalter, George K. Skouroumounis. 1997.]</ref>.
===Acidic Hydrolysis===
Aglycones can be released from glycosides via a low pH. Generally, this occurs at lower pH's and 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>.
* See also: [[Hops#Glycosides|Glycosides In Hops]].
===Beta-Glucosidase===
Aglycones can also be released chemically from glycosides by either exposure to acid (generally pH of 3 or lower, and different pH's giving different results on which glycosides are broken down; this breakdown of glycosides under low pH has been linked to the slow flavor development of aging wine <ref name="Maicas"></ref>), or by enzymes called beta-glucosidases. Enzymatic breakdown of glycosides has been described as producing a more "natural" flavor in wines versus acidic breakdown. Some fruits have been observed (mostly wine grapes) to have limited beta-glucosidase activity within themselves, however it has been observed as being unstable and having low activity at the low pH of wine and sour beer <ref name="Maicas"></ref>.
Beta-glycosidase enzymes can be added artificially, however there has been much interest in the natural capability of microorganisms to produce beta-glucosidases, particularly 1,4-β-glucosidase <ref name="Winterhalter"></ref>. Microorganisms that can break down glycosides by using beta-glucosidases can then access the resulting sugars for fermentation <ref name="Steensels">[http://www.sciencedirect.com/science/article/pii/S0168160515001865 Brettanomyces yeasts — From spoilage organisms to valuable contributors to industrial fermentations. Jan Steensels, Luk Daenen, Philippe Malcorps, Guy Derdelinckx, Hubert Verachtert, Kevin J. Verstrepen. International Journal of Food Microbiology Volume 206, 3 August 2015, Pages 24–38.]</ref>. There are two major categories of glucosidase activity: endogenous and exogenous. Endogenous enzymatic activity takes place inside of the cell, and exogenous enzymatic activity takes place outside of the cell. Bacteria and fungi that show endogenous glucosidase activity have been shown not to be effective in alcoholic fermentation due to not tolerating low pH (optimum pH of 5), glucose, and/or ethanol. Generally, the flavorless glycosides remain unaffected by yeast fermentation, leaving them unused as a potential source for flavor and aroma <ref name="Winterhalter"></ref>.
Different types of beta-glucosidase enzymes have different optimal pH and temperatures. For example, beta-glucosidase produced from ''A. niger'' is optimal at a pH of 4.5 and a temperature of 58°C (136°F), whereas the enzyme for ''Brettanomyces anomalus'' is optimal at a pH of 5.75 and a temperature of 37°C (98°F) (it was active to some extent between 15°-55°C). The beta-glucosidase enzyme ceases effectiveness below a pH of 4.5 for one strain of ''B anomalus'' studied <ref name="Vervoort"></ref>.
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>. Many strains of ''B. bruxellensis'' have also been found to have varying degrees of intracellular (produced inside the cell only) or parietal (attached to the cell wall) beta-glucosidase activity. At least one mutant strain of ''B. bruxellensis'' found in wine (''D. bruxellensis'' BCRC920084 from the Bioresource Collection and Research Center, Hsin-Chu, Taiwan) has been reported to have high extracellular (excreted out of the cell) production of beta-glucosidase that was very efficient at breaking down a glycoside called "piceid" that released resveratrol, which has been marketed as a dietary supplement <ref>[https://www.ncbi.nlm.nih.gov/pubmed/29389552?dopt=Abstract Characterization of an extracellular β-glucosidase from Dekkera bruxellensis for resveratrol production. Kuo HP, Wang R, Huang CY, Lai JT, Lo YC, Huang ST. 2018.]</ref><ref>[https://en.wikipedia.org/wiki/Resveratrol Wikipedia. "Resveratrol" article. Retrieved 02/09/2018.]</ref>. ''Brettanomyces'' has more strains that can produce beta-glucosidase than other genera of yeast, and the strains generally also have a higher rate of beta-glucosidase activity than other genera of yeast <ref>[http://link.springer.com/article/10.1038/sj.jim.2900720 Quantification of glycosidase activities in selected yeasts and lactic acid bacteria. H McMahon, B W Zoecklein, K Fugelsang, Y Jasinski. 1999.]</ref><ref name="Mansfield"></ref>. Strains with higher beta-glucosidase activity have been isolated from lambic, suggesting that these strains may have an adapted ability to utilize sugar from glycosides <ref name="Vervoort">[http://onlinelibrary.wiley.com/wol1/doi/10.1111/jam.13200/abstract Characterization of the recombinant Brettanomyces anomalus β-glucosidase and its potential for bioflavoring. Yannick Vervoort, Beatriz Herrera-Malaver, Stijn Mertens, Victor Guadalupe Medina, Jorge Duitama, Lotte Michiels, Guy Derdelinckx, Karin Voordeckers, and Kevin J. Verstrepen. 2016.]</ref>. Some ''Brettanomyces'' strains may only be capable of beta-glucosidase activity, and not the other enzymes which are needed to break down disaccharide type glycosides. Additionally, cell death and autolysis can result in an increase in beta-glucosidase activity in solution due to the cell contents being released into solution <ref name="Mansfield"></ref>. Strains that can metabolize cellobiose tend to also have higher beta-glucosidase activity because they possess an extra gene for beta-glucosidase enzyme production <ref name="Crauwels1">[http://link.springer.com/article/10.1007/s00253-015-6769-9 Comparative phenomics and targeted use of genomics reveals variation in carbon and nitrogen assimilation among different Brettanomyces bruxellensis strains. S. Crauwels, A. Van Assche, R. de Jonge, A. R. Borneman, C. Verreth, P. Troels, G. De Samblanx, K. Marchal, Y. Van de Peer, K. A. Willems, K. J. Verstrepen, C. D. Curtin, B. Lievens. 2015]</ref>. Sensory analysis of beers with cherries or hops have shown that there is a significantly detectable difference between cherry beers that have been exposed to beta-glucosidase from one strain of ''B. anomalus'' versus not exposed to the enzyme, but no significant difference was found in beers hopped with pellets. The cherry beers exposed to the enzyme contained more and above odor threshold eugenol (clove, honey aroma), benzyl alcohol (sweet, flower), benzaldehyde (almond, cherry) than cherry beers that were not exposed to the enzyme. The cherry beers exposed to the enzyme were not only identified in a blind tasting, but were also preferred to the cherry beers without exposure to the enzyme, indicating that beta-glucosidase activity in cherry beers provides a significant flavor difference. Other types of beta-glucosidase enzymes released different levels of different flavor compounds, indicating that the source (bacteria or yeast) of the enzyme make a significant difference in the flavors that are produced <ref name="Vervoort"></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 limited. 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. Terpineol, 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>. Wang et al. (2018) reported another type of glycosidic activity in one strain of ''B bruxellensis'' which is the conversion of the glycoside "mogroside V" into an artificial sweetener called siamenoside I. Other yeast and bacteria species were tested and did not find this particular glycosidic activity. [https://en.wikipedia.org/wiki/Mogroside Mogroside V] is found naturally in some fruit, specifically, an Asian fruit called [https://en.wikipedia.org/wiki/Siraitia_grosvenorii Lo Han Kuo (''Siraitia grosvenorii'')]. The artificial sweetener siamenoside is 563 times sweeter tasting than 5% sucrose. The specific enzyme responsible for this conversion that this strain of ''B. bruxellensis'' produced is called ''Db''Exg1 <ref>[https://www.sciencedirect.com/science/article/pii/S0308814618317473 Dekkera bruxellensis, a beer yeast that specifically bioconverts mogroside extracts into the intense natural sweetener siamenoside I. Reuben Wang, Yi-Chieh Chen, Yun-Ju Lai, Ting-Jang Lu, Shyue-Tsong Huang, Yi-Chen Lo. 2018. DOI: https://doi.org/10.1016/j.foodchem.2018.09.163.]</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>. ===Activity of Lactic Acid Bacteria===(To do) http://www.icfsnmalaysia2017.org/ICFSN2017%20proceedings%20-%20pp%2054-60.pdf https://search.proquest.com/docview/752091646?pq-origsite=gscholar https://www.researchgate.net/profile/Prafulla_Mahajan/publication/225362291_Production_of_Cell_Membrane-Bound_a-_and_b-Glucosidase_by_Lactobacillus_acidophilus/links/55fd56cd08aeba1d9f56bdbd.pdf http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2009.04461.x/full https://ifst.onlinelibrary.wiley.com/doi/abs/10.1111/jfpp.16368 https://www.mdpi.com/2076-3921/11/2/305
===Cyanogenic Glycosides===
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 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>.
After being released from cyanogenic glycosides, HCN is highly toxic to animals. The human body is used to breaking down trace amounts of cyanide into the less toxic substance thiocyanate with an enzyme called rhodanese, which then leaves the body via urination <ref name="Gleadow_2014">[http://www.annualreviews.org/doi/full/10.1146/annurev-arplant-050213-040027 Cyanogenic Glycosides: Synthesis, Physiology, and Phenotypic Plasticity. Roslyn M. Gleadow and Birger Lindberg Møller. 2014.]</ref>. Although there are more than 3,000 plant species that are cyanogenic (a number of them cultivated by farmers perhaps because their cyanogenic properties deter animals from eating them), only a few parts of plants that are considered foods contain enough HCN from cyanogenic glycosides to be considered dangerous (generally, other forms of cyanide are considered more dangerous, such as from exposure to air or water that is polluted with cyanide) <ref name="CDC1">[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf Toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Retrieved 08/25/2016.]</ref>. The location of the cyanogenic glycosides and the enzymes that release them are often each located in different (or all) parts of plants, and those locations are diverse across species. In some plants, the cyanogenic glycosides are concentrated in the stems or leaves of the plant and not the seeds (e.g. sorghum, barley, and lima beans). In fruits sometimes the seeds contain concentrated amounts (e.g. black cherry pits), and other times in the fruit itself (e.g. ''Passiflora edulis''). In rosaceous stone fruits, cyanogenic glycosides are located in the seeds, but the beta-glucosidase enzyme that the plant uses to release HCN is located in the roots of the plant. The concentration of cyanogenic glycosides is generally higher in seedling plants compared to mature plants, however there are a few exceptions where this is the opposite (e.g. some ''Eucalyptus'' species, and lima beans). The HCN potential of plants varies highly depending on the species, strain, and climate/environmental conditions of the crop year <ref name="Gleadow_2014"></ref>.
Although rare, there have been a few reported deaths due to cyanide poisoning from foods containing cyanogenic glycosides. These reports include deaths from elderberry juice that was thought to contain stems and/or leaves (the stems and leaves contain much higher cyanogenic glycosides than the berries, and ripe berries by themselves are considered safe) <ref>[http://www.cdc.gov/mmwr/preview/mmwrhtml/00000311.htm Poisoning from Elderberry Juice -- California. CDC website. 1998. Retrieved 08/30/2016.]</ref>, apricot kernels (pits), choke cherry pits, and improperly processed cassava (a staple food in parts of North Africa) <ref name="who"></ref>. A lethal dosage of cyanide in humans is estimated to be around 1.52 mg per kilogram of body weight, with 0.56 mg per kilogram of body weight being the lowest recorded (although this lowest figure was obtained from a historical case when the measurements taken may not have been accurate) <ref>[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf Toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Pg 42. Retrieved 08/25/2016.]</ref>. High exposure can cause light-headedness, nausea, vomiting, stomach cramps, diarrhea, convulsions, harm to the brain and heart, comas, and death. Exposure to 0.05 mg of cyanide per kilogram of body weight per day for 15-364 days is considered to be the minimum accumulative cyanide exposure by the US CDC. Accumulative exposure can cause health risks, such as reproductive, respiratory, neurological, thyroid, and gastrointestinal issues <ref>[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf Toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Pg 21. Retrieved 08/25/2016.]</ref>. In some foods, such as marzipan and persipan (made from bitter apricot seeds), the processing of this food destroys the natural beta-glucosidase enzyme (which denatures at 75°C), leaving the flora in the human gut to break down the cyanogenic glycosides. Even if an abnormally large portion of marzipan or persipan is ingested, the lack of beta-glucosidase along with the high calories in the food acts as a slow release of cyanide into the human body which the body can deal with <ref>[http://link.springer.com/article/10.1007%2Fs00204-015-1479-8 Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans. Klaus Abraham, Thorsten Buhrke, Alfonso Lampen. 2015.]</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, which . 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 and 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. Some cyanogenic foods can have their cyanogenic glycosides reduced by cooking them at 230°C for 15 minutes (flaxseed, for example) <ref name="Chaouali"></ref><ref name="flax"></ref>, however some amygdalin based cyanogenic plants may have their amygdalin content reduced to about 25% by cooking alone (apricot seeds, for example; only the cooking temperature of 100°C was tested <ref name="tuncel"></ref>). Fermentation by certain species of microbes can have a greater effect on reducing amygdalin to HCN than cooking alone. Microbes that have been shown to break down amygdalin include some species of lactic acid bacteria including ''Lactobacillus plantarum'', and fungi such as ''Endomyces fibuliger'', ''Pichia etchellsii'', and ''Hanseniaspora valbyensis''. Some strains of ''Brettanomyces'' that have high beta-glucosidase activity might be able to break down amygdalin by around 64%, and some strains of ''S. cerevisiae'' might be able to break down up to around 10% of amygdalin, but this needs to be verified by science. Once the amygdalin is broken down into HCN, the HCN can then be volatilized off by cooking in a ventilated space <ref>[http://link.springer.com/article/10.1007/BF00151870 Simple screening procedure for microorganisms to degrade amygdalin. L. Brimer, G. Tunçel, M. J. R. Nout. 1993.]</ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/7710917 Microbial degradation of amygdalin of bitter apricot seeds (Prunus armeniaca). Nout MJ, Tunçel G, Brimer L. 1995.]</ref><ref name="Daenen1"></ref>. In normal brewing procedures, however, the beer is not cooked nor ventilated, so any HCN that is produced by the breakdown of cyanogenic glycosides should be presumed to remain in the beer.
{| class="wikitable sortable"
| Cherries with pit || 6.5-9.1 <ref name="daenen"></ref> || Amygdalin <ref name="Gleadow_2014"></ref>
|-
| Cherry pits only (black) || 161 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />|-| Cherry pits only (red) || 233 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />|-| Cherry pits only (morello) || 3900 <ref name="VOLDŘICH_1992" /> || Amygdalin <ref name="VOLDŘICH_1992" />|-| Apricot pits, wet weight || 89-2170 (depends on region/speciesvariety) <ref name="Chaouali"></ref><ref name="who"></ref> || Amgydalin <ref name="Gleadow_2014"></ref>
|-
| Sweet Apricots with kernel (14-24 fruits for 1 kg; single kernel avg weight is 6 grams <ref name="calapricot">[http://www.califapricot.com/marking_regulations.html California Apricots. Marking Regulations. Retrieved 09/01/16.]</ref>) || 4.2 - 7.2 (avg 0.3 mg per kernel <ref name="wiki_apric_kernel">[https://en.wikipedia.org/wiki/Apricot_kernel "Apricot Kernel". Wikipedia. Retrieved 09/01/2016.]</ref>) || Amygdalin <ref name="Gleadow_2014"></ref>
| Bitter Apricots with kernel (14-24 fruits for 1 kg; single kernel avg weight is 6 grams <ref name="calapricot"></ref>) || 25.2 - 43.2 (avg 1.8 mg per kernel <ref name="wiki_apric_kernel"></ref>) || Amygdalin <ref name="Gleadow_2014"></ref>
|-
| 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>
|-
| Elderberries (fully ripe; under-ripe will contain more) || 30 <ref name="nordicfoodlab"></ref> || Sambunigrin (or sometimes prunasin, holocalin, or zierin) <ref name="elderflowers"></ref>
|-
| Peach seeds/kernels || 54-2600 (variety dependent; mostly reported between 54-666) <ref name="VOLDŘICH_1992">[https://www.scopus.com/record/display.uri?eid=2-s2.0-84987336720&origin=inward&txGid=713c7a86664b8d2865e54a25eaafc9b5 Cyanogenesis in Canned Stone Fruits. VOLDŘICH, M., KYZLINK, V. 1992. DOI: 10.1111/j.1365-2621.1992.tb05446.x.]</ref><ref name="Bolarinwa_2014">[https://www.sciencedirect.com/science/article/pii/S0308814613016245 Amygdalin content of seeds, kernels and food products commercially-available in the UK. Islamiyat F. Bolarinwa, Caroline Orfila, Michael R.A. Morgan. 2014. DOI: https://doi.org/10.1016/j.foodchem.2013.11.002.]</ref><ref>[https://www.scopus.com/record/display.uri?eid=2-s2.0-0021674858&origin=inward&txGid=ee159dc998e0469bc88f0685e8d41ecb The cyanide content of laetrile preparations, apricot, peach and apple seeds. Holzbecher, M.D., Moss, M.A., Ellenberger, H.A 1984.]</ref> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Nectarine seeds (summer fire) || 7.2 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Plum seeds (green) || 1050 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Plum seeds (black; firar black) || 600 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Plum seeds (purple; larry anne) || 130 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Plum seeds (yellow; son gold) || 92 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Plum seeds (red; laetitia) || 26 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Apple seeds (royal gala) || 178 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Pear (conference) || 77 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| Non-Rosaceae fruit seeds (courgette, cucumber, marrow, honey dew melon, squash varieties) || 0.6-12.6 <ref name="Bolarinwa_2014" /> || Amygdalin <ref name="Bolarinwa_2014" />
|-
| '''Commercial fruit juices'''
==See Also==
===Additional Articles on MTF Wiki===
* [[Hops#Hop_Derived_Compounds_In_Beer_and_Biotransformations|Hop Biotransformations]]
* [[Brettanomyces]]
* [[Pediococcus]]
* [[Mixed Fermentation]]
* [[Soured Fruit Beer]]
* [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.]
* [http://nordicfoodlab.org/blog/2013/10/elder-a-love-story "Elder: a love story", by Justine de Valicourt (cyanide in elderberries).]
* [http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0013/111190/prussic-acid-poisoning-in-livestock.pdf Overview of HCN in various grass/straw/hay/livestock feed species.]
* [http://scottjanish.com/?s=glycosides Scott Janish blog articles about glycosides.]
==References==