The tranya that Balok served the crew was, in fact, grapefruit juice, which young Clint Howard absolutely hated. He said in an interview that he had to work very hard at making it look like he actually liked it. (TOS Season 1 DVD special features)
In 'Star Trek Memories' (p. 110), William Shatner claims that tranya was composed of 'warm, food-colored apricot juice'.
"The Comedy Central Roast of William Shatner" implied that tranya could be an addictive beverage and that Balok had developed a bit of a drinking problem.