The relationship between chemical structure and odor is one of the most interesting areas of our profession, made all the more interesting by the fact that it is still only dimly understood. Some categories of chemicals behave in a more or less predictable fashion but others exhibit startling variability.
Thiazoles are a good example of the latter category. In general, the members of the thiazole family tend towards roasted notes, often with meaty connotations. In this article, we will examine two thiazoles that are structurally similar to each other but have radically different aromas, both from each other and from most of the rest of the family.
Note that the rates given throughout this article are the levels suggested for use in flavors intended to be dosed at 0.05% in a ready-to-drink beverages or simple bouillon.
2-Isobutyl thiazole (FEMA# 3134, CAS# 18640-74-9) is, like most members of the thiazole family, somewhat sulfury in character. However, unlike most members of the family, its sulfur note is almost obscured by a predominantly green odor character. This green note is specifically characteristic of tomatoes, more particularly reminiscent of the smell of tomato stems and foliage than of ripe tomatoes.
This chemical is so specific to tomatoes that it is difficult to imagine a tomato flavor without it. The unfortunate corollary is that it is almost equally difficult to imagine it in any other flavor category. This is short-sighted, however, as there are a number of flavor categories where 2-isobutyl thiazole can make a useful contribution.
Tomato: As noted, 2-isobutyl thiazole is frequently added to tomato flavors at quite high levels. And why not? It is intensely reminiscent of tomatoes, so “the more the merrier” seems to be the best approach.
High levels, in the region of 500 ppm, certainly work well but they always give the impression of fresh tomatoes—and sometimes that freshness fades into a degree of rawness. Most uses of tomato flavor are better-suited to a less fresh profile and are better served by a more modest level of addition of around 40 ppm.
Asparagus: The green notes of asparagus are much more intricate than those of tomato but this ingredient can be effective at fairly similar levels, around 20 ppm.
Blackcurrant: At first sight, this quintessentially vegetable ingredient would seem ill-suited to blackcurrant flavors. In practice, it significantly adds to the impression of authenticity and enhances the blackcurrant skin notes. The ideal level of addition depends on the profile of the flavor. Very catty flavors can accommodate up to 50 ppm but more restrained and realistic flavors are better served by 10 ppm.
Papaya: 2-Isobutyl thiazole has some applicability to many tropical flavors but especially papaya. The ideal level of addition is in the region of 20 ppm.
Melon: 20 ppm also works well in all types of melon flavors, providing an intriguing counter-balance to the many other green notes traditionally used in this group of flavors.
Raspberry: Just a touch of this ingredient can transform a mundane raspberry flavor into something more mouth-watering and fresh; 5 ppm is a good starting point.
Roast beef: Green notes of any description might seem out of place in roast beef and other meat flavors but this ingredient can add a nice level of complexity at around 2 ppm.
Fresh lime: Even smaller additions of 2-isobutyl thiazole can enhance all citrus flavors but they are most effective in fresh lime and lemon-lime flavors. Levels are difficult to judge but 0.2 ppm is a reasonable place to start.
2-Isopropyl 4-Methyl Thiazole
2-Isopropyl 4-methyl thiazole (FEMA# 3555, CAS# 15679-13-7) is also somewhat sulfury in profile with distinct vegetal and tropical notes. However, its effect in dilution is to generate an amazing resemblance to the “fuzzy” character of peach skin.
This unique attribute has made this chemical almost indispensible in peach flavors but it also tends to obscure the interesting potential of this unusual note in other flavor categories. While some of the following fruit flavor uses are not really surprising, the brown flavor uses are, I think, much less obvious.
Peach: 2-Isopropyl 4-methyl thiazole is so effective in peach flavors that there is a tendency to add too much; 200 ppm is a pretty good level but more subtle effects can still be obtained at around 50 ppm.
Apricot: There is temptation to simply regard apricot flavors as an offshoot of peach flavors. Many of the important ingredients are the same but the balance is quite different. In this case, the ideal level of this ingredient is lower, at around 100 ppm.
Nectarine: Similar comments apply here but nectarine skin is visibly less “fuzzy” and, unsurprisingly, the ideal level of 2-isopropyl 4-methyl thiazole is even more modest, around 50 ppm.
Durian: To most Westerners, the profile of durian flavors is utterly dominated by very volatile and pungent sulfur notes. It would seem incredible that as little as 20 ppm of 2-isopropyl 4-methyl thiazole would make the slightest bit of difference to this leviathan, but it does.
Mango: Mango skin has a quite different character from peach skin, and much of that profile derives from ocimene and myrcene. Despite this major difference, this ingredient is surprisingly useful at levels in the region of 10 ppm, enhancing the authenticity of the skin note without actually shifting its direction.
Pear: Even lower levels, around 5 ppm, can have a small but noticeable effect on the authenticity of pear by enhancing the perception of pear skin in Williams-type pear flavors.
Blackcurrant: Authentic style blackcurrant flavors can benefit in very much the same way from the addition of 5 ppm of 2-isopropyl 4-methyl thiazole, giving improved realism and skin notes.
Tea: 2-Isopropyl 4-methyl thiazole is also effective in black, red and green tea flavors but it really comes into its own in green tea profiles. Levels of addition can be quite high, up to 50 ppm, but lower levels around 20 ppm are more harmonious. Ideal levels in black and red tea flavors are even lower, at around 5 ppm.
Cocoa and chocolate: It is hard to achieve the natural character of cocoa nibs without the inclusion of process flavors. However, process flavors carry the significant disadvantage that they often seem to have a typical, easily recognizable profile. 2-Isopropyl 4-methyl thiazole veers from this problem by giving the impression of cocoa nibs, especially the husks, at levels of addition in the region of 10 ppm.
Coffee: Finally, coffee flavors are similarly difficult to make truly characteristic of freshly ground coffee beans using entirely synthetic raw materials. Just 10 ppm of this raw material also helps in this profile, adding significant authenticity.