Lexical to gustatory synesthesia is one of the rarer types of synesthesia. The synesthete with lexical to gustatory synesthesia experiences specific flavors associated with particular spoken or heard words and phonemes. It has also been reported that these synesthetes sometimes associate temperatures with words. Research suggests that this type of synesthesia begins with early food experiences, and tastes are often triggered by a corresponding food name, e.g., "apple" tastes like apple (Simner & Ward, 2006). For some synesthetes, simply thinking about a trigger word will produce its flavor. While flavors often appear for phonemes as well, they tend not to be as predictable or as intense as trigger words (Ward, et al., 2005). Some lexical-gustatory synesthetes even experience flavors semantically, wherein (for example) the word "blue" tastes "inky" or "shell" tastes "shiny".
Simner, J., and Ward, J. (2006). The taste of words on the tip of the tongue. Nature, 444(7118), 438.
Ward, J., Simner, J., and Auyeung, V. (2005). A comparison of lexical-gustatory and grapheme-colour synaesthesia. Cognitive Neuropsychology, 22(1), 28–41.