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Added new section "Acidic hydrolysis"
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, 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 aging of wine <ref name="Maicas"></ref>.
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, 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, 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 glycosdes <ref>[HowLowpH Can Intensify ?-Damascenone and Dimethyl Trisulfide Production through Beer Aging. L AURENCE G IJS , F ABIENNE C HEVANCE , V ESNA J ERKOVIC , AND S ONIA C OLLIN. 2002. DOI: 10.1021/jf020563p.]</ref>.
* See also: [[http://www.milkthefunk.com/wiki/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>.