Reading the data · 16
The strength field is not a threshold: 354 materials say high, and their recommended dilutions span a thousandfold
· 17 min read
Two ethyl esters in this database have almost the same supplier count: ethyl butyrate at 102 and ethyl 2-methyl butyrate at 104. The strength field separates them sharply, though. The first reads high, evaluate at 1% or less; the second reads medium, evaluate at 10% or less, a tenfold difference. The literature puts them the other way round. A 2016 stable isotope dilution study of mango named ethyl 2-methylbutanoate among the most potent compounds it found, with ethyl butanoate in the same group at an OAV of 980. A 2024 paper on ancient Chinese apple cultivars states directly that ethyl 2-methylbutyrate has an extremely low odour threshold. This is not a contradiction: the two fields answer different questions. Spread out all 2,451 records carrying a strength field and it becomes clear. 1,649 of them give no concentration at all, only an adjective, and of the 354 marked high the recommended dilution splits into 1% for 163, 10% for 145, 0.10% for 37, 5% for 4 and 0.01% for 3, a thousandfold range under one word. This piece covers what the strength field actually is, how it differs from an OAV, and how to use it.
About a 4 minute read.
Too long, didn't read
- 2,451 materials carry a strength field; 1,649 of them give only an adjective, no concentration
- The 354 marked high split across 1%, 10%, 0.10%, 5% and 0.01%, a thousandfold range
- Ethyl butyrate reads "high, 1% or less"; ethyl 2-methyl butyrate reads "medium, 10% or less", a tenfold gap
- The literature ranks those two the other way round
- Nobody is wrong. A recommended evaluation dilution is not an odour threshold, and the two numbers answer different questions; the evaluation dilution field really answers only a yes-or-no
Two esters, a tenfold gap in the strength field
Start with this pair. Both are fruity esters, almost the same supplier count, both recording 4 hours of longevity:
| Ethyl butyrate | Ethyl 2-methyl butyrate | |
|---|---|---|
| CAS | 105-54-4 | 7452-79-1 |
| Formula | C6H12O2 | C7H14O2 |
| Suppliers | 102 | 104 |
| Odor family | fruity | fruity |
| Descriptors | fruity, juicy fruit, pineapple, cognac, sweet | sharp, sweet, green, apple, fruity, estery, berry |
| Strength field | high, evaluate at 1.00% or less | medium, evaluate at 10.00% or less |
| Longevity | 4 hours | 4 hours |
| Vapour pressure | 12.8 mmHg | 7.853 mmHg (est) |
Read that field alone and the inference is natural: ethyl butyrate has to be diluted ten times further before you can smell it, so it must be the stronger of the two.
The literature puts them the other way round
In 2016 Munafo and colleagues quantified tree-ripened mango ('Haden') in J Agric Food Chem (PMID 27167034). The method was stable isotope dilution quantitation of 34 aroma-active compounds previously identified with high flavour dilution factors, followed by an odour activity value (OAV) for each, defined as the ratio of its concentration in the mangoes to its odour threshold in water.
24 compounds came out with an OAV above 1. Among the most potent, the authors named ethyl 2-methylbutanoate, ethyl 3-methylbutanoate (fruity, OAV 1600), and ethyl butanoate (fruity, OAV 980).
So in that system, ethyl 2-methylbutanoate stands in the same front rank as ethyl butanoate, and ethyl butanoate's 980 is not the highest of the group.
In 2024, Lu and colleagues, working on the ancient Chinese apple cultivars 'Binzi' and 'Xiangguo' (PMID 39335800), put it more directly: ethyl 2-methylbutyrate has an extremely low odour threshold.
The ordering on the literature side runs opposite to the impression the strength field gives.
What the strength field actually is
Spread the whole database out and the shape of this field becomes clear.
2,451 materials carry a strength field. The adjectives:
| Adjective | Count |
|---|---|
| medium | 1,513 |
| high | 354 |
| none | 318 |
| low | 253 |
| very (very high and similar) | 13 |
1,649 of those give no concentration at all, just the adjective. Among the 802 that do, 10% appears 527 times, 1% appears 204 times, 0.10% appears 45 times, 50% appears 12 times and 0.01% appears 9 times.
The telling cell is this one. The 354 marked high split into five different recommended dilutions:
| Recommended dilution | Count |
|---|---|
| 1.00% | 163 |
| 10.00% | 145 |
| 0.10% | 37 |
| 5.00% | 4 |
| 0.01% | 3 |
From 0.01% to 10%, a thousandfold range, all of it called high.
Medium is looser still: 1,082 give no concentration, and among those that do, 378 say 10%, 38 say 1%, and 11 say 50%, a material labelled medium strength while being recommended for evaluation at half concentration.
A field that spans a thousandfold under one label is not a measurement. It is a piece of working advice.
An OAV and a recommended dilution answer different questions
Put the two definitions side by side and it resolves.
OAV = the concentration of a material in some food ÷ its odour threshold in water. It answers: "does this compound contribute to the smell of that mango, and how much?" The numerator is a quantitation of a real sample; the denominator is a human detection limit.
Recommended evaluation dilution answers: "how far should a perfumer dilute this before smelling it on a blotter to get useful work out of it?" Several things feed into that, and only one of them is the threshold:
- Whether the neat material is so sharp that the detail is lost
- How fast it evaporates (dilute something too volatile and there is nothing left to catch)
- The evaluation habits of the supplier and the cataloguer
- The threshold
Point 1 often outweighs point 4. Neat ethyl butyrate is a hard estery blast, and 1% is recommended so that a person can hear "pineapple" instead of just ester. Ethyl 2-methylbutyrate has the lower threshold, but its neat character is easier to read, and 10% is workable.
What strength should I smell it at is about the working side; odour thresholds is about the measurement side. This field belongs to the first.
So how should the field be used
- Treat it as a starting dilution, not a strength ranking. It tells you where to begin smelling, not who will dominate whom in a formula.
- Before comparing across materials, check whether a concentration is given at all. 1,649 records carry only an adjective, and comparing "medium" against "high" is comparing two uncalibrated labels.
- Within one adjective, read the concentration. Two materials both marked high, one at 0.01% and one at 10%, are a thousandfold apart.
- To judge actual contribution in a formula you want an OAV or a threshold, not this field. And this database has no threshold column.
- The 45 records asking for 0.10% or less are worth remembering separately as the strictest bracket here; 3-mercaptohexyl acetate is one of them.
→ Search by odour: 42,225 materials, with strength, longevity and physical data.
What this article does not establish
- "Neat ethyl butyrate is harsher, hence 1%" is my reading, not the catalogue's. There is no record of how this field was decided.
- In the record I retrieved, the OAV figure for ethyl 2-methylbutanoate was cut out of Munafo's abstract. I cite only that it was named among the most potent, plus the 1600 and 980 explicitly given for the other two.
- OAVs are system-dependent. A ranking in mango does not transfer automatically to apple, to a perfume, or to a blotter.
- Both papers work in food matrices, not alcoholic formulas and not skin.
- The strength field statistics cover only the 2,451 records that filled it, not all 42,225.