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====Monoterpenes and Glycosides====
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>. Monoterpenes can also be odorless polyols, some of which can break down easily to produce pleasent 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 produce monoterpenes during fermentation separately from freeing monoterpenes from glycosides <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>.
Glycosides are a very diverse group of non-volatile and flavorless molecules that generally encompass any molecule that has a sugar bound to a non-sugar molecule (thus separating them from polysaccharides). The sugar (monosaccharide or oligosaccharide) component of the molecule is known as the "glycone", and the non-sugar component is known as the "aglycone". By breaking the glycosidic bond of a glycoside, the aglycone component is released. The aglycone component of glycosides are often polyphenols or the floral monoterpene alcohols described above. Glycosides can be categorized based on their glycone (glucose vs fructose), type of glycosidic bond (α-glycosides or β-glycosides), or by their aglycone (alcoholic, anthraquinone, coumarin, cyanogenic, flavonoid, phenolic, aponins, steroidal/cardiac, steviol, or thioglycosides). Glycosides play important roles in living organisms, especially many types of plants which store glycosides in their tissue and then break the bond between the sugar and non-sugar aglycone when the aglycone is needed for certain biological functions <ref>[http://www.newworldencyclopedia.org/entry/Glycoside "Glycoside." New World Encyclopedia. Retrieved 05/06/2016.]</ref>. These include protecting cells from toxins in the plant and attracting insects via the fragrance of flowers <ref name="Winterhalter"></ref>.