Food dyes are used in many common beverages and foods. While food dyes serve no nutritional purpose, they provide an attractive color to many different drinks, desserts, and even meat. Nowadays, most of the population use the microwave to heat the food and because almost every comercial product containes one or more food dyes, we saw the necessity of a study regarding the thermal behaviour of there dyes at different temperatures, using three types of spectroscopy: Thz-TDS, FTIR and UV-Vis-NIR absorption spectroscopy. We studied five food dyes in aqueous solutions: E 102-Tartrazine, E 110-Sunset Yellow, E 122-Azorubine, E 124-Red Ponceanu, E 155-Brun HT. Spectrophotometers are also used in the food industry where many foods are colored using federally specified and approved food dyes. Because these food dyes have been given rigorous chemical inspection, they have many properties that are well documented and that can be used to easily identify them. Also, the refractive index for these food dyes was determined in the same range of temperatures.