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I've searched a lot for this, but I still cannot find any good explanations for how these two factors affect flavonoid concentrations.

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  • $\begingroup$ This looks on topic here (not sure), but if you're interested in techniques for brewing tea/etc, you may like our site for Homebrewing :) $\endgroup$ – ManishEarth Jul 1 '12 at 3:00
  • $\begingroup$ By "how", do you mean "what is the mechanism behind..." (in which case a few more details on the observed effects would be useful), or "what are the effects of ..." (in which case it looks offtopic, not too sure)? $\endgroup$ – ManishEarth Jul 1 '12 at 3:25
  • $\begingroup$ @Manishearth Ah, but at its core, brewing tea is really an exercise in extraction techniques. $\endgroup$ – jonsca Jul 1 '12 at 5:16
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You might want to have a look at

J. Peterson et al., Major flavonoids in dry tea, Journal of Food Composition and Analysis, 2005, 18, 487--501, http://dx.doi.org/10.1016/j.jfca.2004.05.006

and the references therein, e.g.

Christiane Lakenbrink et al., Flavonoids and Other Polyphenols in Consumer Brews of Tea and Other Caffeinated Beverages, J. Agric. Food Chem., 2000, 48*, 2848--2852, http://dx.doi.org/10.1021/jf9908042

From the abstract of the latter:

[...] At brew times up to 2 min the composition of the brew solids was for each product practically independent of brew time, with flavonoids again comprising the major proportion (86−88%) of the total phenolics. [...]

Longer extraction times (> 10 min) or continuous (Soxhlet) extraction lead to partial decomposition of the flavonoids, most likely due to phenolic oxidation, cf.

Won Jo Cheong et al., Determination of Catechin Compounds in Korean Green Tea Infusions under Various Extraction Conditions by High Performance Liquid Chromatography, Bull. Korean. Chem. Soc., 2005, 26, 747--754, http://dx.doi.org/10.5012/bkcs.2005.26.5.747

I hope that helps a bit.

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