Black tea from Assam's North Bank tested brighter and more caffeinated than Upper Assam's, the Tocklai Tea Research Institute reported in its first regional quality benchmark in over a decade.

The study, published January 3 in the journal Foods, measured 32 black teas, 20 from Upper Assam and 12 from the north bank of the Brahmaputra, under standard ISO test methods, covering both the older orthodox process and the modern CTC crush. Tocklai, at Jorhat, is the world's oldest tea research institute, and its authors said no comparable regional survey had been done in more than ten years.

The gap the office notes first is theaflavins, the compounds a taster ties to brightness and briskness in a black cup. North Bank teas averaged 9.18 milligrams per gram against Upper Assam's 8.03, the study reported. The north-bank samples also carried more caffeine, 32.91 milligrams per gram against 28.40, which the authors read as a mark of younger, finer leaf. On total polyphenols the north bank again averaged higher, 150.29 against 131.15, while Upper Assam's figures scattered more widely from sample to sample.

Processing method changed the character less than the region did. Orthodox and CTC teas gave up almost the same water-soluble extract, 404.34 milligrams per gram against 407.91, so both routes delivered comparable strength to the cup. Every sample cleared the national and ISO limits for safety and quality.

By weight and measure, then, the north bank's leaf brought more of what a laboratory counts as brightness and strength. Both belts passed. One simply weighed heavier on the markers a black-tea drinker looks for.

Sources: Sarmah et al., "Biochemical Quality Profile of Black Tea from Upper Assam and North Bank Region of Assam, India", Foods (January 3, 2026) | en.