Three habits when evaluating, two of which do nothing

Someone asked an open question on r/DIYfragrance: "What is something that annoys you as a perfumer?"

Sixty-two replies. Most are about how other people treat the craft — five-minute perfumes, longevity questions, naturals being safer.

And buried in the complaints are three specific habits, all three of which can be checked.

The short version

• Sniffing the cap or the atomiser does nothing useful. What is on there is dried residue, and evaporation has already stripped the volatile part out of it.
• Resetting your nose with coffee beans does nothing, and this has been tested. Grosofsky and colleagues had participants sniff coffee beans, lemon slices or plain air after nine rounds of fragrance rating, then do an identification task — coffee beans did not yield better performance than lemon slices or air.
• The reason lies in the mechanism. Dalton's 2000 review states it plainly: olfactory adaptation is stimulus-specific, and sensitivity recovers over time in the absence of further exposure. What you need is time and distance, not another smell.
• The same review has a useful practical detail: stimulating one nostril adapts both, though the exposed side is more affected and recovers more slowly. Switching nostrils is not a reset.
• Judging in ten seconds judges a fraction of the formula. Matching the corpus against the database's substantivity field: materials lasting under 24 hours make up 25.4% of the median formula's data-covered weight.
• The thread also carries a very concrete problem three people hit independently: black plastic atomiser parts smelling fishy after contact with alcohol.

About 9 minutes.

One: sniffing the cap

This one drew 14 upvotes:

"When I hand someone a small tester bottle, they pull off the cap and sniff the atomizer, as if that will tell them everything they need to know about how the perfume will smell."

Somebody added the reason underneath:

"Never smell a perfume by sniffing just the cap or the atomizer. It's all the dried up juice that you smell."

That explanation is right, and the reasoning is worth spelling out.

The residue on a nozzle or a cap has been sitting in air, evaporating. Evaporation is not proportional — low-boiling, short-lasting components leave first and the heavy ones remain. We've written about the evaporation curve.

So the nozzle is not a concentrated version of the perfume. It is a very old drydown of it. You are smelling what that perfume looks like four hours in, on a surface with no skin, no body heat and no dilution.

And it might not even be the perfume you are smelling.

The fishy atomiser

The thread contains a small side story that three people hit separately.

Haven416:

"I just got a bunch of 2mL sprayers (glass bottles/plastic atomizers and caps) and after I made up a whole bunch of testers, I noticed an almost fishy smell when I first removed the caps to try them out. It's the plastic, not the perfume obviously, but that certainly doesn't make a good first impression!"

Annual_Impression834, writing in Polish:

"I have exactly the same. The black plastic part of the atomiser stinks of fish after contact with alcohol."

Sad-Committee-1870:

"Yeah if you find a better alternative let me know. Not all of mine do that for some reason, but… even one or two is off putting."

Three people, different places, the same description: black plastic, contact with alcohol, a fishy smell.

A fishy smell has a narrow origin in odour chemistry: amines, particularly the trimethylamine family. And plastic processing aids — slip agents, antistatics, certain amine antioxidants — are extractable into ethanol.

To be clear: I have not tested any of those atomisers, and I found no research on this. That sentence is a mechanistically coherent guess rather than a verified answer.

What can be done is clear enough:

1. Soak new atomisers in ethanol before use. Then smell the ethanol.
2. Discard a whole batch that shows it. One of the three said not all of theirs do it, which points to a batch problem rather than a design problem.
3. Keep an eye on black parts. Two of the three mention black. That could be carbon black or its dispersant, and it could be coincidence.

Your packaging is part of your formula. It is easy to miss when working alone, because a large manufacturer runs packaging compatibility tests and you do not.

Two: coffee beans

This one drew 12 upvotes and offered a specific alternative:

"I think educating the consumer better. It's an old trope to have coffee as the 'neutralizer.' Coffee smells like coffee, it's not a true neutral. Instead, smell the curve of your elbow or your jacket. Your own smell is mostly neutral to you and helps to 'reset' between sniffs."

Somebody put "coffee is not neutral" to an experiment.

Grosofsky and colleagues wrote it up in Perceptual and Motor Skills in 2011, and their opening is the practice itself: fragrance sellers often provide coffee beans to their customers as a "nasal palate cleanser", to reduce the effects of olfactory adaptation and habituation.

The method is simple. College students smelled three fragrances repeatedly, rating them each time. After completing nine trials, participants sniffed coffee beans, lemon slices, or plain air. They were then presented with four fragrances and asked which had not been smelled before.

The result is one sentence:

Coffee beans did not yield better performance than lemon slices or air.

All three groups the same.

It is an exploratory study, the participants were students, and the task was identification rather than evaluating a perfume — limits I list at the end. What it does establish is that the practice is unproven, and that the one time it was tested no effect turned up.

Why coffee cannot work

Grosofsky found no effect. Dalton's 2000 review in Chemical Senses explains why there would not be one.

That review sets out the psychophysics of olfactory adaptation, and the key sentences are:

Repeated or prolonged exposure to an odorant typically leads to stimulus-specific decreases in olfactory sensitivity to that odorant, but sensitivity recovers over time in the absence of further exposure.

"Stimulus-specific" and "recovers over time" between them rule coffee out of the job.

• Adaptation is to the thing you just smelled.
• Recovery happens through absence of further exposure, which means time.
• Smelling something else does not speed that up. It only starts adapting you to that too.

The review adds that the magnitude and time course of adaptation and recovery depend on the concentration of the odour and the duration of exposure — so the stronger and longer you smelled, the longer the wait.

And this line is the most useful of all in practice:

Monorhinal stimulation results in adaptation in both the ipsilateral and contralateral nostril, although the degree of adaptation in the ipsilateral nostril is more profound and recovery is slower.

Switching nostrils is not a reset. Both get tired; one gets tired faster.

(The review also notes that adaptation occurs at multiple levels, peripheral at the receptor and more central beyond it, and that most psychophysical studies have not separated the two. So "take a break" works for more than one reason.)

The commenter's suggestion of smelling your own elbow or jacket is a different kind of thing from coffee beans. That is not a competing odour so much as returning to your own background, which you are already adapted to. It is closer to leaving than to cleaning. That direction is compatible with Dalton's mechanism, though I found no study testing it directly.

Three: the first ten seconds

This one drew 18 upvotes and is the shortest reply in the thread:

"When people judge a perfume by the first 10 seconds on a strip."

This can be quantified.

Matching the 954 public formulas against the database's substantivity field and keeping only formulas where at least half the weight matched a substantivity record, 569 remain (median data coverage 72.0%). Sorting into bands by how much of that covered weight each represents:

Substantivity	Median share of covered weight	Interquartile range
< 24 hours	25.4%	8.8%-46.7%
24-100 hours	21.9%	8.0%-37.2%
100-300 hours	14.7%	3.4%-29.9%
≥ 300 hours	14.4%	2.6%-35.4%

Materials lasting under 24 hours account for a quarter of the median formula's weight.

Read that table carefully. Substantivity measures how long something lasts on a blotter at a stated concentration; it is not a time-course of the mixture. A long-lasting material is in the bottle and on the blotter from the first second too. The table does not say "you haven't smelled three quarters of it" — it says the formula's weight sits mostly in the part you are not in a hurry to judge.

Which is precisely what the commenter is complaining about. Someone who walks away after ten seconds is skipping the part the formulator spent the most weight on.

(Related: we ran the numbers on the eight-hour standard, and the top-voted reply in this thread at 45 points makes the same complaint: "The assumption that something must last at least 8 hours or it's considered cheap or poorly made.")

Collecting it up

Three habits, two of which do nothing:

Habit	Status
Sniffing the cap / atomiser	Useless, and you may be smelling packaging
Resetting with coffee	Tested, no better than air
Judging in ten seconds	Skips three quarters of the weight

The things that do work are boring: wait, leave the room, come back in a few hours, try it on skin, write down the time. We've written about keeping evaluation notes.

The best line in the thread is not about technique. Someone asked what it takes to count as a perfumer, and the original poster answered by borrowing from Jean-Claude Ellena:

"Sometimes even a bad sketch is better than having none."

What this doesn't establish

The atomiser section has no research behind it. Those three comments are three people's reports, I have tested no atomisers, and I found no literature on extractables from plastic atomisers in ethanol. The amine mechanism is a coherent guess, written up here because it points to a concrete action (soak in ethanol first), not because it is established.

Grosofsky's study is exploratory. The participants were college students, the task was "which one is new" rather than evaluating a perfume, and the abstract does not state a sample size. "No difference detected" is not "proven to have no effect" — I cannot judge the study's statistical power from the abstract.

That study measured identification performance, not whether things smell clearer. Those are related and not the same.

Dalton's review is from 2000. Two decades of work followed and I read only that paper, so this presents what that review compiled rather than the field's current state.

I found no direct study of the elbow-sniffing idea. It is a commenter's practice, and it is compatible with Dalton's mechanism — compatible is not validated.

The substantivity table carries three limits. First, only 569 formulas were usable (the rest had materials with no substantivity record), and those 569 need not be a random subset. Second, median data coverage is 72.0%, so 28% of the weight sits outside the calculation. Third, substantivity values are measured under inconsistent conditions — some neat, some at 10% dilution, as we've written elsewhere. The table is good for relative magnitudes and not for precise proportions.

Substantivity is not "when you can smell it". A material lasting 400 hours is present in the first second too; it simply does not dominate. I put that in the body because it is easy to misread.

References

A. Grosofsky, M. L. Haupert, S. W. Versteeg, An exploratory investigation of coffee and lemon scents and odor identification, Perceptual and Motor Skills, 112(2), 536-538 (2011). PMID 21667761. doi:10.2466/24.PMS.112.2.536-538

P. Dalton, Psychophysical and behavioral characteristics of olfactory adaptation, Chemical Senses, 25(4), 487-492 (2000). PMID 10944515. doi:10.1093/chemse/25.4.487

Related: the evaporation curve, olfactory fatigue, the eight-hour standard, keeping evaluation notes.