In 1879 Fahlberg, working with Remsen in a post-doctoral capacity, made an accidental discovery that changed Remsen's career. Eating rolls at dinner after a long day in the lab researching coal tar derivatives, Fahlberg noticed that the rolls tasted initially sweet but then bitter. Since his wife tasted nothing strange about the rolls, Fahlberg tasted his fingers and noticed that the bitter taste was probably from one of the chemicals in his lab. The next day at his lab he tasted the chemicals that he had been working with the previous day and discovered that it was the oxidation of o-toluenesulfonamide he had tasted the previous evening. He named the substance saccharin and he and his research partner Remsen published their finding in 1880. Later Remsen became angry after Fahlberg, in patenting saccharin, claimed that he alone had discovered saccharin. Remsen had no interest in the commercial success of saccharin, from which Fahlberg profited, but he was incensed at the perceived dishonesty of not crediting him as the head of the laboratory.
Throughout his academic career, Remsen was known as an excellent teacher, rigorous in his expectations but patient with the beginner. "His lectures to beginners were models of didactic exposition, and many of his graduate students owe much of their later success in their own lecture rooms to the pedagogical training received from attendance upon Remsen's lectures to freshmen."
In 1901 Remsen was appointed the president of Johns Hopkins, where he proceeded to found a School of Engineering and helped establish the school as a research university. He introduced many of the German laboratory techniques he had learned and wrote several important chemistry textbooks. In 1912 he stepped down as president, due to ill health, and retired to Carmel, California.
In 1946, to commemorate the centenary of Remsen, the Maryland chapter of the American Chemical Society, began awarding the Remsen award, in his honor. Awardees are frequently of the highest caliber, and included a sequence of 16 Nobel laureates between 1950 and 1980.
^Burgison, Raymond M. (1 May 1957). "The Remsen Memorial Lecture 1946-1957"(PDF). Chesapeake Chemist. 13 (5): 9-10. Retrieved 2018. It was the intention of the Maryland Section that Remsen Memorial Lecturers should be chemists of outstanding ability, as exemplified by Ira Remsen's long and devoted career as an exponent of the highest standard in teaching and reserach [sic] in chemistry. That the intentions of the Section have been fulfilled is attested by the great honor and esteem that have become associated with the receipt of the Remsen Lectureship.
^ abHartford, Winslow H. (1946). "Ira Remsen and Roger Adams--A Chemical Centennial". The Scientific Monthly. 63 (4): 261-267. Bibcode:1946SciMo..63..261H. JSTOR18751. The year 1946 marks the one-hundredth anniversary of the birth of Ira Remsen, first professor of chemistry and second president of The Johns Hopkins University. The chemists of Maryland, through the Maryland Section of the American Chemical Society, have appropriately chosen this year to initiate a series of lectures in his honor, and Professor Roger Adams of the University of Illinois was selected as the first Remsen Lecturer.
^"F. A. Cotton Medal: K. B. Sharpless / Remsen Award: E. A. Carter / Janssen Pharmaceutica Prize for Creativity in Organic Synthesis: J. F. Hartwig". Angewandte Chemie International Edition. 53 (25): 6306. 12 June 2014. doi:10.1002/anie.201405110. ISSN1433-7851.
^"Leadlay, Prof. Peter Francis, (born 13 Dec. 1949), Herchel Smith Professor of Biochemistry, University of Cambridge, since 2006; Fellow of Clare College, Cambridge, since 1979; Co-Founder and Director, BIOTICA Technology Ltd, 1996-2013", Who's Who, Oxford University Press, 1 December 2007, doi:10.1093/ww/9780199540884.013.u24043