Material guide: buchu mercaptan — Cramer Class III, toxicity 'not determined', 89 suppliers, and 0.2 ppm in a beverage

About a 4 minute read.

The short version

• Name: buchu mercaptan, p-menth-8-thiol-3-one, CAS 38462-22-5, FEMA 3177
• Odour type: sulfurous; odour: sulfurous, minty, green, fruity, berry, buchu, tropical, peach, raspberry
• Strength: high (evaluate at 1% or less), rank 3; substantivity > 120 hours at 100%
• Suppliers: 89 — the most of any Cramer Class III material
• Oral toxicity field: not determined
• Beverage use level: 0.2–0.4 ppm

One molecule spanning sulfur and fruit

The odour field lists sulfurous alongside peach, berry and raspberry. That is uncommon.

odor_descriptions holds four entries; two of them capture the turn:

Buchu, green, and blackcurrant leaf. Minty, green, fruity, berry-like, buchu with a fruity tropical and peach nuance.

characteristic cassis (black currant); herbal, fruity green sulfury.

This is that smell. Blackcurrant's aroma has always carried a trace of cat-pee inside the fruit, and thiols are its chemical basis.

The notes field adds one line that matters for buying:

A mixture of stereoisomers is used as a blackcurrant flavour.

What you buy is not a single isomer. (The occurrence field names one natural source: buchu leaf oil.)

It is Cramer Class III

structure_class reads III.

I measured this field in a separate article: only 5.1% of the database carries a Cramer class, and Class III holds 335 records — buchu mercaptan is the best-supplied of them, at 89.

And 32.2% of Class III materials have sulfur in the name, against 12.8% in Class I. This material is the pattern's exemplar.

But Class III does not mean toxic. It means the structure offers no basis for presuming safety — the tree could not place it in a low-concern box, so the conversation has to move to intake.

And its toxicity field really is empty

toxicity_oral: Not determined.

No LD50, no dose of any kind.

This is exactly the situation Class III exists to handle: neither structural confidence nor measured data. And yet the material is FEMA GRAS (3177), listed with JECFA, and carries four EFSA flavouring group evaluations (FGE.08, FGE.08 Rev 1, FGE.91).

So how does it pass?

Through the use level

taste_descriptions contains something rare in this series — a complete dosage ladder:

Used in blackcurrant, grape, and berry flavours; in desserts at up to 6 ppm, bakery and soft confections at 1–2 ppm, and in beverages at 0.2 ppm to 0.4 ppm.

Three product categories, three different ceilings. The beverage figure of 0.2 ppm is a thirtieth of the dessert figure.

This is what the toxicological procedure looks like in the concrete. The Cramer class decides which threshold applies, and that threshold is compared against an estimated intake. EFSA's 2022 FGE.07, evaluating 55 substances, states the usual outcome plainly: none of the 55 gives rise to safety concerns at estimated dietary intake levels.

The system does not ask whether this is dangerous. It asks whether it is dangerous at this use level.

(Okamura and colleagues' 2015 paper shows the other half of the same thing: five acetal flavourings, none with a genotoxicity structural alert, split by Cramer into Class I and Class III — sorted by structure, not by evidence.)

And its substantivity was measured neat

odor_substantivity: > 120 hours at 100.00%

Last time I corrected myself about reading the concentration after an hour figure. This record was measured neat, so its 120 hours can be compared directly with birch tar's 400.

And the greater-than sign means 120 is a floor — it had not gone when they stopped watching.

How to use it

• Evaluate at 1% or less. Rank 3, and it is a thiol.
• It is the core of blackcurrant, raspberry and tropical fruit, but the dose belongs on a ppm scale.
• Check whether you are buying the isomer mixture or a single isomer. The notes field says commerce uses the mixture.
• In perfume it is a trace fruity modifier. cosmetic_uses reads perfuming agents, but the odour field's first word is sulfurous — the consequence of overdosing is not subtle.
• 12 months, cool and dry. (Despite being a sulfur compound, it is not among the 145 records told to refrigerate.)

What this doesn't establish

• I have not smelled it. This is fields, whole-database statistics, and two papers.
• Neither paper is about this material. I cite them to explain how the Cramer classification and the TTC procedure work, not because they evaluated buchu mercaptan.
• The dosage ladder is a statement inside a field; I did not trace its source or learn which regulatory jurisdiction it describes.
• "Blackcurrant's cat-pee facet comes from thiols" is prior knowledge, not established from this record.
• The toxicity field is empty, so I have no dose to cite — everything above about safety is about the procedure, not about measured data for this material.
• I did not check its IFRA text.