Editing Cider apple (section)

===Other classification considerations===
Beyond the Long Ashton or English system and French system for classifying cider apples, there are other considerations for characterisation. Other measurements taken of apple varieties towards use in cider classification include pH, polyphenol composition, [[yeast assimilable nitrogen]] (YAN),<ref name="fifth" /> and soluble solid concentration (ºBrix).<ref>Michigan Apple Committee. [http://www.canr.msu.edu/productcenter/uploads/files/makecider.pdf How to make cider]. Retrieved 27 April 2018.</ref> The sharpness of an apple is affected by pH and [[titratable acid]]ity. Most cultivars must reach pH levels of around 3.3 to 3.8 to aid in the fermentation process, and additions of malic acid may be necessary if the cider apple is over this desired threshold. Soluble solids as measured in units of degrees Brix can be used to quantify the potential alcohol that a yeast can ferment from the initial juice of the cider apple. This is carefully considered in cultivars from areas where there are tax regulations on the percentage of alcohol by volume that is contained in these products. In the United States, "hard cider" legally falls between the 0.5% to 8.5% alcohol by volume tax bracket.<ref>[https://docs.house.gov/billsthisweek/20151214/121515.250_xml.pdf Protecting Americans from Tax Hikes Act of 2015], Pub. L. No. 114-113, 129 Stat. 2244 (2015)</ref> Cideries that exceed a soluble solids level of 17 °Brix will be subject to higher tax levels that are classified under cider wine.<ref name="last" /> In the United Kingdom, cider falls in two duty brackets, with a flat rate for up to 7.4% ABV, and a higher duty rate for ciders between 7.4% to 8.5% ABV.<ref>More about cider and perry. [http://www.camra.org.uk/en_US/more-about Campaign for Real Ale.] (2014).</ref> Foaming is an intricate, yet essential component that can be used to assess the overall quality of a cider and distinguish between natural and sparkling ciders. Chemically, hydrophobic polypeptides contribute to the initial foam, bubble size, the extent to which it persists, number of nucleation sites, and the froth of the foam (foam collar). These chemical compositions and parameters are quantitatively measured through metrics such as foam height, foam stability height, and stability time.<ref>Blanco-Gomis, D., Mangas-Alonso, J. J., Expósito-Cimadevilla, Y., & Gutiérrez-Álvarez, M. D. (2010). [https://web.archive.org/web/20180517005729/https://pdfs.semanticscholar.org/b09f/a48607df6e4ea397b8d4d9c3160a8db09420.pdf Characterization of cider by its hydrophobic protein profile and foam parameters]. Food Chemistry, 121, 220-226.</ref> The olfactory sensory profile is used to determine the specific aroma of the cider. Research is still ongoing in this field, but the aromas that contribute to the sensory perceptions of cider mainly come from the phenols 4-ethyl guaiacol and 4-ethyl phenol.<ref>Antón, M. J., Valles, B. S., Hevia, A. G., & Lobo, A. P. (2013). Aromatic profile of ciders by chemical quantitative, gas chromatography-olfactometry, and sensory analysis. Journal of Food Science, 79, S92-S99.</ref>