Material guide · 29
Material guide: rose oxide — the rose you smell when peeling a lychee, and a class reunion in one paper
· 16 min read
CAS 16409-43-1, the lead of the green, metallic rose scent inside lychee shells. A 1999 study compared lychee with Gewurztraminer wine and found 12 shared odor-active compounds, with cis-rose oxide holding the highest odor activity value among the shared odorants of all three; half the list are alumni of this series. A 2008 study adds stereochemistry: fermentation shifts its enantiomeric ratio. 77 suppliers, high strength with a 1%-or-less evaluation advice, a top note lasting past 8 hours.
Peel a lychee in summer and the moment the shell cracks, a scent escapes: rose, with an edge of green and a cool metallic touch. Not your imagination. One of the leads of lychee's aroma is rose oxide, the same molecule that works as a trace heavyweight in rose oil — fragrance-chemistry common knowledge.
What matters
- Rose oxide is the rose's green metallic edge, and a lead player in lychee. High strength; the database says evaluate at 1% or less. A pure top note lasting past 8 hours.
- A 1999 study compared lychee with Gewurztraminer wine: among 12 shared odor-active compounds, cis-rose oxide carried the highest odor activity value. Lychee, rose and white wine are three faces of the same cast of molecules.
- Exactly half that shared list are alumni of this series: beta-damascenone, linalool, geraniol, citronellol, PEA and vanillin all answer the roll call. One paper threw a class reunion.
The record
| CAS | 16409-43-1 |
| Formula | C₁₀H₁₈O |
| MW | 154.25 |
| Odour | green, red rose, spicy, fresh, geranium, vegetable, floral, herbal, camphoreous |
| Odour family | floral |
| Strength | high (evaluate at 1% or less) |
| Substantivity | > 8 h (neat, on a strip) |
| Specific gravity | 0.865–0.873 (25 °C) |
| Flash point | 69 °C |
| Registers | GRAS, JECFA, CoE, FEMA GRAS, IFRA |
Plain reading: CAS is the material's ID number. Another member joins the 1%-evaluation club (banana ester, decanal and galbanum are already in it). The ">" in the substantivity row means the source only vouches for it lasting past 8 hours; its post is still the opening act.
Lychee, rose, white wine: three faces of one cast
Gewurztraminer's most famous tasting note is "lychee". In 1999, Ong and Acree in the Journal of Agricultural and Food Chemistry took that tasting note apart into molecules:
Comparing GC/O results of canned lychee, fresh lychee and Gewurztraminer wine, 12 common odor-active volatile compounds were found in all three: cis-rose oxide, ethyl hexanoate/ethyl isohexanoate, β-damascenone, linalool, ethyl isobutyrate, geraniol, ethyl 2-methylbutyrate, 2-phenylethanol, furaneol, vanillin, citronellol and phenethyl acetate. On the basis of odor activity values, cis-rose oxide had the highest values among the common odorants in the three products, indicating its importance to the aroma of both lychee fruit and Gewurztraminer wines. […] No cis-rose oxide was detected in the control wines (Chardonnay and Riesling).
Read that list again: beta-damascenone, linalool, geraniol, citronellol, PEA, vanillin, and, on the canned lychee's main-contributor list, delta-decalactone. Twenty-nine articles in, one paper calls a whole row of this series' familiar faces to attendance. The more materials you know, the more such lists read as names rather than formulas — which is exactly what a starter palette is for.
Fermentation rewrites its stereochemistry
Rose oxide comes as cis/trans isomers, each with left- and right-handed enantiomers whose smell can differ — the advanced class of the linalool article's laevo-versus-racemic lesson. In 2008, Koslitz and colleagues measured the stereo-composition in wine:
Quantified by stable isotope dilution, cis-rose oxide was present in all white wines studied (0.2 to 12 micrograms per litre), highest in Gewurztraminer varieties. […] The enantiomeric ratio of cis-rose oxide in all investigated wines was substantially lower than in nonfermented musts. Fermentation experiments showed yeast reducing geranyl diol precursors to citronellyl diol, with acid-catalysed cyclisation then forming cis- and trans-rose oxide; deuterium labelling demonstrated at least two different reductive pathways in yeast yielding cis-rose oxide with different enantiomeric ratios.
Plainly: the same molecule enters the fermentation tank and comes out with its left-right ratio rewritten by the yeast. On a catalogue, the (Z)- (that is, cis-) and laevo- prefixes are not decoration; they mark different stereo-versions with different smells. The batch variation homework runs two layers deep on this material.
Smelling it
- Evaluate at 1% or less, per the database. My first sniff at 10% registered only metal and camphor; the lychee shell appeared at 0.5%.
- The rose accord's second finishing drop: after the trio builds the body and beta-damascenone brings the jam, a few tenths of a percent of rose oxide adds the raw green of a freshly cut rose stem.
- For lychee, white-grape or rosewater directions it is the defining material; with citronellol and a touch of sweetness the accord stands.
- A top note lasting past 8 hours, an opening-act character like cis-3-hexenol; it hands over after the first act.
The catalogue family
| Item | What it is |
|---|---|
| (Z)-rose oxide (77 suppliers) | the material itself: the cis isomer, lychee-rose green |
| laevo-rose oxide (8 suppliers) | the single laevorotatory enantiomer, more precise and more expensive |
| dihydrorose oxide (2 suppliers) | the hydrogenated version, a softer green |
A small family, but every prefix earns its place: (Z) marks cis/trans, laevo marks handedness. This material's name is a pocket exercise in stereochemistry.
Regulatory
Listed on GRAS, JECFA, CoE, FEMA GRAS, IFRA. As always, registers carry no limit values. For skin formulae, consult the current IFRA Standards and the supplier's specification.
Buying it
- The smallest bottle is plenty; at 1%-evaluation strength, doses run in tenths of a percent.
- Start with (Z)-rose oxide; the laevo version is the upgrade path once your formula proves it needs it.
- Add citronellol to the cart while you are at it, and the lychee-rose skeleton is complete.
→ Rose oxide in the database: full properties, supplier list, suggested pairings. → Laevo-rose oxide | Citronellol | Search by odour: try "rose green" for its neighbours.
References
P. K. Ong & T. E. Acree, Similarities in the aroma chemistry of Gewürztraminer variety wines and lychee (Litchi chinesis Sonn.) fruit, Journal of Agricultural and Food Chemistry, 47(2), 665–670 (1999). PMID 10563950
S. Koslitz, L. Renaud, M. Kohler & M. Wüst, Stereoselective formation of the varietal aroma compound rose oxide during alcoholic fermentation, Journal of Agricultural and Food Chemistry, 56(4), 1371–1375 (2008). PMID 18247534