Truffle oil traditionally is made from submerging truffles in olive oil or heating it in a vacuum. The oil will taste different depending on the variety of truffle used, and the variety of olive oil, or grape seed oil used. Doing this draws the essence of the truffles out and into the oil. Do be careful of botulism. Some who sell truffle oil actually do not use truffles at all and instead inject a chemical compound 2,4 dithiapentane into the oil to produce a similar one dimensional flavor at reduced cost.