1. Food and Agriculture Organization of the United Nations (2019) FAOSTAT, Crops and livestock products, Tea https://www.fao.org/faostat/en/#data/QCL/visualize
2. Leitsätze für Tee, teeähnliche Erzeugnisse, deren Extrakte und Zubereitungen vom 2.12.1998 (BAnz. Nr. 66a vom 9.4.1999, GMBl. Nr. 11 S.228 vom 26.4.1999), zuletzt geändert am 5.3.2013 (BAnz. AT vom 12.12.2013 B6, GMBl. Nr. 63 S.1265 vom 17.12.2013) [Guidelines for tea, tea-like products, their extracts and preparations from 02.12.1998 (BAnz. No. 66a from 9.4.1999, GMBl. No. 11 p.228 from 26.4.1999), last amended on 5.3.2013 (BAnz. AT from 12.12.2013 B6, GMBl. No. 63 p.1265 from 17.12.2013)]
3. Indian Tea Association: Orthodox Grades https://www.indiatea.org/orthodox and Standardization of grades of CTC teas (as specified by Tea Board from 1st March 2011) https://www.indiatea.org/ctc_tea_grade
4. REGULATION (EU) 2017/625 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 15 March 2017 on official controls and other official activities performed to ensure the application of food and feed law, rules on animal health and welfare, plant health and plant protection products, amending Regulations (EC) No 999/2001, (EC) No 396/2005, (EC) No 1069/2009, (EC) No 1107/2009, (EU) No 1151/2012, (EU) No 652/2014, (EU) 2016/429 and (EU) 2016/2031 of the European Parliament and of the Council, Council Regulations (EC) No 1/2005 and (EC) No 1099/2009 and Council Directives 98/58/EC, 1999/74/EC, 2007/43/EC, 2008/119/EC and 2008/120/EC, and repealing Regulations (EC) No 854/2004 and (EC) No 882/2004 of the European Parliament and of the Council, Council Directives 89/608/EEC, 89/662/EEC, 90/425/EEC, 91/496/EEC, 96/23/EC, 96/93/EC and 97/78/EC and Council Decision 92/438/EEC (Official Controls Regulation)
5. Shevchuk A, Jayasinghe L, Kuhnert N (2018) Differentiation of black tea infusions according to origin, processing and botanical varieties using multivariate statistical analysis of LC-MS data. Food Res Int 109:387–402. https://doi.org/10.1016/j.foodres.2018.03.059