An attractive addition of 2-ethyl-4-methylthiazole to authentic pistachio flavors is 50 ppm.
Predictability is not really in the cards for the thiazole family. This makes them a very interesting chemical category. Odors range quite dramatically from roasted and nutty, through peach skins, to tomato leaves. 2-Ethyl-4-methylthiazole (FEMA# 3680, CAS# 15679-12-6) has some roasted aspects, but it is quite specifically nutty and cocoa in character. There is also an interesting second link to 2-isopropyl-4-methylthiazole, a closely related thiazole, which gives especially interesting results in fruit flavors. These connections mean that 2-ethyl-4-methylthiazole can be used in a very wide range of different flavors, often in combination with other related notes.
