My experience here was 22 years ago, so I'm sure the state of the art and the instrumentation has advanced significantly since then. They were evaluating FT-NIR spectroscopy when I was there, and undoubtedly they have gone much further. They may well be using LC-MS-MS time of flight on every sample now, for all I know, to identify and quantify every single organic molecule. By the way, little if any of this is a "trade secret". The analyses are largely standardised across the industry (and validated using reference laboratories), and the taste training reference sets are commercial products.

I later did a PhD in areas including developmental biology and immunology, and went to some talks by researchers on fly olfactory receptors and memory, which I'll come back to. I didn't do research in this area myself (I was looking at vascular development); it was seminars from visiting researchers. So bear in mind this is secondhand!

I think your comments about sensory experience, differences between people with different genetic backgrounds and so on are pretty much how I understand things myself.

Smell is one of the most, if not the most, primitive senses in the body. While we can philosophise about whether individuals experience the world in the same way, and proving it one way or another is very difficult, if not impossible, a great deal of this basic sense is essentially "hardwired". One of the best talks I went to was from a researcher using genetically modified insects with fluorescently-labelled neurons, which lit up when activated but were also visible when inactive as well (IIRC they used two colours). What was really interesting here was that under the microscope, they could visualise, in real-time, the olfactory receptors, the neural structure linking it to the brain, primarily the area associated with memory. What really struck me was that this was effectively (in computer terms) like the address lines on a memory bus. Each different olfactory receptor appeared to activate a different combination of neurons. Kind of like high and low voltages on lines on a parallel bus. That directly activated a response, be it innate or learned. That could be a danger signal, triggering an immediate physical response e.g. "jump", or positive e.g. "food". I did ask the question about the parallel with computer systems, because it just looked so obvious, but they (rightly) said that it certainly looked that way, but it would take a lot more work to prove. And in biological systems, information transmission is often based on frequency encoding rather than simple on or off, so who knows, but I found this absolutely fascinating. And it makes one wonder whether the "address lines" are wired up randomly and you learn from experience, or if they are actually effectively hardcoded, or a combination of the two. I wouldn't be surprised if it was the latter.

So I think that if we can draw a parallel from insect to human senses (and I think, at the physical level things will likely be very conserved for such a primitive sense), we have a large repertoire of receptors, connected directly to the brain, likely memory to elicit an immediate learned response. I suspect our experiences will be largely the same bar genetic differences around selected receptors, kind of like red-green colourblindness. We will have a combination of innate and learned responses to given stimuli. We all have an immediate and negative reaction to certain "danger" signals. While having a varied response to others; I imagine there's both a genetic and learned components here.

You're absolutely right about "gain". When doing the tasting we would have a stack of dry "table water" biscuits to "reset" the palate. You can really tell the difference, though it's subtle.

In terms of different perceptions between individuals, that's the main reason for training with a "reference set" of chemical compounds. It makes it objective instead of subjective. You learn to detect each one in complete isolation, and if you're completely physically incapable of detecting it, you should be able to pick up on that. Maybe like red-green colourblindness you can compensate for it if other similar receptors are slightly stimulated? I don't know. Either way, that standardised reference set should mean that everyone is trained to the same standard and knows that "this taste is this named flavour", even if their "experience" of that taste is different (we can never know).

Kind regards,
Roger