Taste (gustation) has as its physical stimulus chemical substances that are dissolvable in water.  Receptors for taste are clusters of cells found in the taste buds, which line the trenches around tiny bumps on the tongue. These cells absorb chemicals, trigger neural impulses, and send the information throughout the thalamus and on to the cortex.
	The four primary tastes are sweet, sour, bitter, and salty, with uneven distribution on the tongue.
	Clearly, taste results from a complex blend of these 4, as well as learned and social processes.