1803, John Browne Cutting, “A Succinct History of Jamaica” in Robert Charles Dallas, The History of the Maroons, London: Longman and Rees, Volume 1, pp. xcv-xcvi, […] when the liquor is reduced sufficiently, so as to be contained in the third smaller copper, it is ladled into that, and so on to the last, called the teache, so named probably from the practice, at this stage of the process, of trying the consistency of the boiled juice by the touch.
Source: wiktionary