Hi jean-luc,
Human sense of taste is usually tied up with aroma.
There are protein based enzymes that drive a conversion processes into terpene molecules; there is a volatile fraction that forms a compound our senses can react to.
One of the most researched is "geosmin", the earthy taste & aroma.
This perfume of dirt is absent in hydroponic produce, since the micro-biota that the geosmin compound is derived from are usually soil dwelling. (It's formation increases & decreases proportionately when pH goes up or down.)
In your search to manipulate taste:
the nutrient factors you should supply are the building block minerals for the unique composition of the terpenes associated with your crop & attend closely to the pH of nutrient solution stability at harvest time (so there is no lock out of those minerals allowing degradation of the volatile compounds).
Many cut back on nutrients prior to harvest, based on the theory of flushing the substrate to let the crop stabilize it's taste. You might want to experiment with cutting down the nitrogen & just keeping up the other terpene components.

Hi gringojay!
Very interesting indeed, and even more complex and technical than expected. I didn't even know about "geosmin", which one may even call the agent for earthy taste & aroma. May clay pellets contain some of it? One may think of custom made clay pellets that are fired at somewhat lower temperatures, the way they do not decompose visibly, but still emit some components. Though, these emissions must be water soluble to be absorbed, right!?

I am already testing a mix of coconut husk and rice husk (with some rough sand) as substrate. There is a slow decomposition of coconut included, rice husk has lots of micro nutrients but is decomposing much slower than coconut husk. Both influence the PH considerably, especially as the decomposition and degradation is kinda expontional after a month or so (for coconut husk only), But as I deal with high evaporation of nutrients, I replace them in huge amounts. My nutrient base is calculated to have the required PH without adds. That's how the PH is no major problem.

By cutting down the nitrogen content you also cut down the calcium content, when using calcium nitrate as main N-source, and that might affect taste negatively, I guess.

Don't you have any sources (links) where your information provides from?

Thanks a bunch!

Hi jean-luc,
Geosmin will be easy for you to find searching the internet; it is not found as a pre-existing compound in the soil or on fired clay pellets (rather generated out of bacteria/etc. byproduct that is a process fostered in the soil).
There are other aromatics like esters, sulphur compounds, etc.
Let me stick to terpenes, which always involve 2 stages (1st hydrocarbon phosphates are coupled & rearranged by an enzyme, then the secondary oxidation of these bonds gives tens of thousands of different terpene compounds).
One of the aromatic catalysts has a structure whose central Hydrogen atom can be replaced by metal ions; such as Iron, Manganese, Copper (think of the 50 different kinds of chlorophyll with it's core Magnesium).
With some of your leaf crops the taste quality has factors other than mineral
content.
Basicly, given adequate day time light exposure the night temperature (not the lack of light) is a key to temperate origen crops' taste. If the night is warm then the actual enzymes involved in aromatic oxidation are adversely affected; ie. cool nights can even favor flavor (one reason why some tropical grown temperate vegetable produce has such disappointing taste, yet tropical vegetables do taste savory ).
As for your goal of improving taste while using cocconut substrate.
Coir (shredded cocconut husk fibre) has a pH range of 5.2 - 6.8, with tendency toward 6+pH (this is the growing medium pH); plus, it is notorious for high Potassium (K) & Manganese(Mn).
You have seen the coir compaction & should consider there are other factors for you to compensate for in quest for improving crop taste.
The coir's soluble salts of K & Mn may build up in your growing medium (consider high Mn obstructs Iron/Fe uptake). You may eventually get these leaching down into your re-circulated nutrient solution & distorting your presumed fertilization ratios.
Trace minerals ( Fe, Mn, Cu, etc.) you want available to form catalysts that will jump start the final transformation of different crops' unique terpene aromatics.
If your nutrient solution (even apart from the substrate) has a high pH then you may also get the potentially dynamic Fe, Mn, Cu, Zn & B locked out (for that matter high pH can lock out P, which is integral to the 1st stage of terpene transformation).
You discuss Calcium; coir is deemed to be low in Ca, yet you must consider what form you are going to be supplying Ca with (you don't want to drive a high pH coir growing medium even higher).

Hi again and muchissimo gracia gringojay,

Well the idea of the (expanded) clay pellet perhaps came a little too spontaneous. Perhaps because I would have means to make such custom pellets. But hence (as you say) the source of Geosmin is not at all mineral but bacterial/organic. In fired clay (which on the other hand is not such a bad idea actually) there obviously is no bacterial/organic matter left.

But then again I have been told that plants actually cannot assimilate any organic substances. Any compound does need to be oxidized, ionized and so on, until it's molecular structure is fine enough to be assimilated by the capilars. Or can one say that these are bind to some of the molecules and find their way "upwards" as a compound? My way of putting it...

What you are saying about warm night temperature makes perfect sense. Actually, tomato plants even suffer from (or may even die with) too high night temperatures. They badly need cool night temperatures as part of their physiology and growing process. Although there are species that are supposed to be selected and cultivated to the end of being able of dealing and growing well with high night temperatures. Though, I bet that these specific cultivars are not the most tasty there are...

Just a few words about coconut husk. The one I use is not shredded, it is cut - sometimes I even cut it myself with a machete. The pieces are small and I eventually came to only use a little amount. But earlier I have had great results with coconut husk only. Before I was able to control PH, I have had great results growing pepper plants with kinda high PH and a way too high, permanently growing nutrient concentration. It's against all rules and odds, but somehow and for quite a long time it worked amazingly well. Actually until first ripening fruits and harvest. But as the plants were growing even bigger, problems obviously started, and the plants suddenly showed heavy symptoms of nutrient deficiency. Eventuelly I had to mercifully stop the experiment. ;-)

Since I am using mainly a mix of rice hulls and Sand, and only "a pinch" of the coconut husk. PH keeps pretty stable, and that's what matters.

I guess that one reason why the "aromatic aspect" with hydroponics is not widely researched yet, is because it's already difficult enough to keep plants healthy and well. In other words, changes that may have a positive influence on taste and flavour, quickly tend to sooner or later cause trouble of some chemical order... in which there actually is not that much room for change and "strange" experiments. ;-)

Thanks again for the most competent and interesting information!

Barely forgot, gringojay - is there a way to contact you personally. I've seen that you live in Dominican Republic and probably have (same as me) to deal with other problems of tropical climate (pests, fungus and such). There may be other common interests.

I guess it is not advised or permitted to post my email address here, isn't it?
And I can't see any PM-feature with this board either.

Any suggestions, in case you are interested?

Hi jean-luc,
This forum is where you can exchange ideas. It also gives a chance for errors posted to be worked out.
People here will reply to your other questions.
(I am late comer to internet & resist email except for family, so don't seek link ups; but then I dislike telephones, wrist watches & driving too.)

I'm pretty sure my beans have always tasted like beans, and my Red Savina habeneros have always been @$$ burning hot, no matter what nutrients I used to grow them.

I don't know what you're so concered about, as any species of plant will tatse how they are genetically pre-dispositioned to taste. ;)

LOL!

Just make sure to feed them properly, and nurture them until they are grown.

The commercial hydroponic product "Floralicious" promoted as "enhances flavor" & boosts "complex secondary aromatic compounds" is not available everywhere ( I worked in Asia 2 years).
It includes 2% humic acid, which has a cation exchange capacity (CEC) +/- 10 times greater than normally found; chelated multiple (++) charged trace mineral ions get more uptake with improved membrane permiability.
If you take the leachate (distinct from aerobic brewed worm casting "tea") from worm bins' drainage run off this has humic acid (as would the tea). The leachate pH can be 7+ ; make sure bin conditions have not gone anaerobic.
Alternately, if you have soft shale (or soft lignite/leonardite) you can bring up the pH to 6.5 - 8.0 (say 25% sodium bicarbonate, or less if use lye/sodium hdroxide) to soak it crushed for 2 days agitated in water (say 50%) to get humic acid into solution & then precipitate the unwanted elements.
In N. Thailand (Chiang Mai was sleepy in mid-1980s) you might only have decaying fresh water drift wood to chop up & work with; the guideline is if that old tree carbon's soak water stains yellow you've got humic acid.
When working with hard water it will require more source substrate & soft water dissolves the humic acid more readily. (The carbonates affect the process & alkaline/hard water classification is not the same as a solution's pH reading.)
Always highly dilute humic acid, because an excess of the plant growth hormones it carries can diminish N,P,K uptake.
Another ingredient of the de-" licious" product is a soil organism to regulate root microbial population & keep the undesireables away; it is bacterial innoculation with Bacillus subtilis.
Bacillus subtilis encompases a wide choice of varieties. Apart from the beneficial human medical implications of different strains, it is commonly living in one form or another in the soil. The USDA maintains a culture bank of freeze dried strains in vials for the public & many universities around the world will be experimenting it. (Scientific supply companies sell cultures of it to secondary school classes for students to learn how to culture benign bacteria in a petri dish with soy broth nutrient.)
As for the other components:
hydrolysed protein is meals of blood (say 50%) , fish bone (say 50%) & poultry feather (say 20%) individually dissolved in enough citric acid ( say 50% each extraction) to lower the pH to free their nitrogen (not as nitrate); seaweed (washed) is the multiple trace minerals source; & mannitol (a long chain carbohydrate, such as those found in mushrooms) is a "sugar" for the bacterial growth that acts acidic to help balance the pH.