Buchu oil can be distilled from either of two closely related plants. Major components of the more common barosma betulina oil are diosphenol (minty peppermint) 20%, limonene (citrus) 9%, menthone (minty peppermint) 15%, iso-menthone (minty peppermint pennyroyal) 25%, para-mentha-8-thiol-3-one (sulfury, catty) 0.5% and pulegone (minty pennyroyal) 15%. The less frequently found, but nevertheless very interesting, barosma crenulata oil typically contains diosphenol (minty peppermint) 0.2%, limonene (citrus) 9%, para-mentha-8-thiol-3-one acetate (sulfury, catty berry) 4%, menthone (minty peppermint) 8%, iso-menthone (minty peppermint pennyroyal) 15% and pulegone (minty pennyroyal) 45%. It can be difficult to differentiate between betulina and crenulata plants because the only real guide is the leaf shape (crenulata leaves are longer).
The profiles of both oils are driven by their key sulfur components. Para-mentha-8-thiol-3-one is very widely used in flavors because its catty note is relatively free from metallic undertones. Para-mentha-8-thiol-3-one acetate (FEMA# 3809, CAS# 57074-34-7), also known as menthone-8-thioacetate or 4-mentha-8-acetyl thiol-3-one, has a very similar odor profile, softer and a little more subdued. However, it has two key virtues which, in my opinion, should encourage much wider use: it is chemically more stable and less prone to H2S loss on storage, and it is also significantly more heat stable.
Note that the dose rates given throughout this article are the levels suggested for use in flavors intended to be dosed at 0.05% in ready-to-drink beverages or in a simple bouillon.
Tropical Fruit Flavors
Guava: The concentrated essence of tomcat that is so characteristic of para-mentha-8-thiol-3-one acetate finds a perfect home in guava flavors, even though the overall character is not overtly catty. With ease, 20 ppm can be accommodated.
Lychee: Lychee flavors are at the other end of the scale. They are often far to light, simple and rose oriented. Just 1 ppm of this ingredient adds sufficient complexity and lifts the character out of the ordinary.
Mango: Mango flavors range across an interesting spectrum from authentic to frankly peach and melon characters. Para-mentha-8-thiol-3-one acetate is equally at home in all these different habitats, and 5 ppm is a good starting level.
Melon, Cantaloupe: In the same way, this chemical can be used in all the many different melon profile, even watermelon, but it is most at home in cantaloupe melon flavors. A good place to start is 8 ppm.
Passionfruit: At first sight, passionfruit flavors seem to be an outlier for para-mentha-8-thiol-3-one acetate. The character is obviously strongly catty, but it is also noticeably metallic. The ideal solution is to use a combination of catty notes. A metallic note to underpin the character and a good splash, even as much as 50 ppm, of para-mentha-8-thiol-3-one acetate to send the catty note through the roof.
Pineapple: Compared to passionfruit, pineapple is quite boring and conservative but a moderate addition, around five ppm, of this ingredient lifts the character nicely and adds authenticity.
Stone Fruit Flavors
Apricot, Fresh: Apricot flavors cover quite a range of different profiles. Those that are frankly more peach than apricot can use quite high levels of para-mentha-8-thiol-3-one acetate, but more authentic profiles are better server by more modest additions, in the region of 2 ppm.
Nectarine: Realistic nectarine flavors are also better served by cautious additions of this ingredient. A reasonable starting point is 4 ppm.
Peach: Extremely effective in all peach flavors, 20 ppm of para-mentha-8-thiol-3-one acetate lifts fresh peach flavors and banishes dullness in more mundane examples of the profile.
Citrus Fruit Flavors
Bergamot: Grapefruit is the only citrus profile that is obviously catty, but bergamot can absorb almost as much catty character as grapefruit without it becoming exactly obvious. A level of 5 ppm in bergamot flavors adds lift and realism. It works equally well in all the bergamot variants in the complex world of Earl Grey tea flavors.
Grapefruit: Para-mentha-8-thiol-3-one acetate should only take a secondary role in the sulfur complex of grapefruit flavors but, even then, it can add lovely lift at around 10 ppm.
Lemon: Just a hint of this component, as little as half a ppm, adds a touch of fresh juice character to grapefruit flavors.
Lime: A little more, around 1 ppm, works in the same way with fresh lime flavors. A similar level is also effective in the rather harsher style of lime flavors based on distilled rather than cold pressed oil.
Mandarin: Mandarin flavors fit into a very similar category to bergamot flavors. They are not obviously catty but 5 ppm of para-mentha-8-thiol-3-one acetate lifts the profile beautifully and adds realism.
Orange, Sweet: Caution is necessary with orange flavors because too obvious an addition of para-mentha 8-thiol-3-one acetate can push the profile strongly in the direction of tangerine. A good startling level is 1 ppm.
Tangerine: In contrast to orange, the level of use in tangerine flavors can be manipulated considerably to obtain broadly different effects. A level of 2 ppm is probably ideal in more subtle flavors.
Berry Fruit Flavors
Blackberry: Just a hint, around half a ppm, is all that is required to brighten and lift a realistic style blackberry flavor out of the ordinary.
Blackcurrant: Now, we are distinctly on home ground, given the historic (over)use of buchu oil in blackcurrant flavors. The level of use of para-mentha-8-thiol-3-one acetate in blackcurrant flavors is a question of taste. A level of 100 ppm packs a considerable punch but does not necessarily detour the profile away from all semblance of authenticity.
Blueberry: Blueberry flavors range from quite floral and delicate to distinctly rustic and bilberry like. This ingredient fits better into the rustic category and adds bite to wild blueberry or bilberry flavors at 2 ppm.
Raspberry: Although raspberry flavors have a strong family connection to blackberry flavors, they are usually somewhat more assertive and can easily accommodate 1 ppm of para-mentha-8-thiol-3-one acetate.
Redcurrant: Redcurrant flavors are not exactly common, but they are of some interest to lovers of pinot noir wines. The character is similarly complex to the profile of good wines with just a couple of years of bottle age. A level of 1 ppm of this chemical is decidedly helpful in recreating that note.
Strawberry: Wild strawberries and very ripe garden strawberries are really quite sulfury and para-mentha-8-thiol-3-one acetate plays an interesting part, along with a complex of aliphatic sulfur esters, at around three ppm.
Other Fruit Flavors
Grape, White: Not all grape flavors are helped by this ingredient, but the grassier white grape types can absorb up to four ppm.
Rhubarb: After a recent trip to the Lake Road Kitchen in Ambleside and trying a creation made with ingredients from the Yorkshire Rhubarb Triangle, it came to me that rhubarb flavors could easily benefit from up to eight ppm of para-mentha-8-thiol-3-one acetate.