Perilla oil
Oil pressed from toasted perilla seeds, deep golden, nutty with a grassy, herbal undertone.
Perilla oil is pressed from the seeds of perilla, a plant of the mint family whose leaves are eaten in Korea as a vegetable and as a wrap; the seeds are usually toasted first. It smells nutty like sesame oil but has its own earthy, grassy, faintly bitter character, which Koreans prize in vegetable side dishes, over rice or brushed onto seaweed. It is a seasoning oil added cold or at the end, not a frying oil, because strong heat drives off its aroma and turns it bitter. Being rich in polyunsaturated fats, it goes rancid faster than most oils, so buy small bottles, keep them in the fridge once opened and use them within a few months. You will find it in Asian shops with a Korean range and through mail order.
Substitute:
Toasted sesame oil is the obvious substitute and works in the same dishes, but it tastes rounder and sweeter, and the herbal, grassy note that defines perilla oil is lost entirely. There is no substitute that captures that note.