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Monoterpenes generally exist as aromatic and flavorful alcohols that tend to smell floral with low odor thresholds (100-400 ppb), and are present in plant material. These alcohols mostly consist of linalool, geraniol, nerol, and linalool oxides, but also includes other monoterpenes such as citronellol, alpha-terpineol, hotrienol, nerol oxide, myrcenol, the ocimenols, and other oxides, aldehydes and hydrocarbons. In wine (and probably sour beer), these alcohols bind with acids to create aromatic monoterpene ethyl esters and acetate esters, and can also be transformed into other types of monoterpenes by yeast metabolism <ref>[http://www.sciencedirect.com/science/article/pii/S0168160510006653 Monoterpene alcohols release and bioconversion by Saccharomyces species and hybrids. A. Gamero, P. Manzanares, A. Querol, C. Belloch. 2011.]</ref><ref name="Daenen2">[http://onlinelibrary.wiley.com/doi/10.1111/j.1567-1364.2008.00421.x/pdf Evaluation of the glycoside hydrolase activity of aBrettanomyces strain on glycosides from sour cherry (Prunus cerasus L.) used in the production of special fruit beers. Luk Daenen, Femke Sterckx, Freddy R. Delvaux, Hubert Verachtert & Guy Derdelinckx. 2007.]</ref>. Monoterpenes can also be odorless polyols, some of which can break down easily to produce pleasant aromas. For example, diendiol can break down into hotrienol (tropical, floral, fennel, ginger aroma <ref>[http://www.thegoodscentscompany.com/data/rw1374491.html "Hotrienol." The Good Scents Company. Retrieved 05/11/2016.]</ref>) and nerol oxide (green, vegetative and floral with a minty undernote <ref>[http://www.thegoodscentscompany.com/data/rw1001891.html "Nerol Oxide." The Good Scents Company. Retrieved 05/11/2016.]</ref>). While some monoterpenes are free within the plant material, around 2-8 times that amount are bound up in flavorless glycosides <ref name="Maicas">[http://link.springer.com/article/10.1007/s00253-004-1806-0/fulltext.html "Hydrolysis of terpenyl glycosides in grape juice and other fruit juices: a review." Sergi Maicas, José Juan Mateo. May 2005.]</ref>. It is thought that some wine strains of ''Saccharomyces cerevisiae'' can might be able to produce monoterpenes such as geraniol during fermentation separately from freeing monoterpenes from glycosides in ways not related to beta-glucosidase activity <ref>[http://femsle.oxfordjournals.org/content/243/1/107.abstract De novo synthesis of monoterpenes by Saccharomyces cerevisiae wine yeasts. Francisco M. Carrau, Karina Medina, Eduardo Boido, Laura Farina, Carina Gaggero, Eduardo Dellacassa, Giuseppe Versini, Paul A. Henschke. 2005.]</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 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>. 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. Most of the All strains of ''S. cerevisiae'', however, did release another enzyme called beta-glucanase, which led to varying degrees of breaking down some smaller glycosides found in hops containing the aglycones methyl salicylate, 1-octen-3-ol, and cis-3-hexen-1-ol, but not linalool. None of the ''B. bruxellensis'' strains showed this activity, but the only tested strain of ''B. custersianus'' and both of the ''B. anomala'' strains tested did show cell-associated (endogenous) beta-glucosidase activity. In particular, the ''B. custersianus'' strain was tested against glycosides from hops, in which case high amounts of the algycones 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. The beta-glucosidase activity remained the same when fermented alone, or when fermented with ''S. cerevisiae''. ''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>. The same strain of ''B. custersianus'' was screened for beta-glucosidase activity and aglycone byproducts during the refermentation of sour cherries in beer (although a very small amount of the byproducts were manufactured by the yeast as a byproduct of fermentation, 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, jasmin 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>.