When building a recipe, here are John Robert's Botanic Request we divide the botanicals into 2 categories: Delicates & Hardy. Delicates are generally zests, teas, leafs, herbs, floral. Our hardy botanicals are generally woody, dried, roots, seeds and grain.
To squeeze a delicate botanical between your fingers you will generally express oils and aroma onto your finger tips and if you were to squeeze a dried woody root you wouldn't get much due to its tough, hardy and dry exterior.
When concentrating on extracting oils, fats, flavour compounds and esters etc from our hardier botanicals we will look at applying a robust and "aggressive"technique : VACUUM PRESSURE MACERATION.
Pulling vacuum pressure on botanicals sat within an alcohol solution; we are aggressively forcing osmosis (osmosis is where we will see the natural occurrence of flavour extraction from steeping/macerating botanicals in alcohol)
The vacuum will change the atmospheric pressure within the sealed container forcing and expelling all natural air and gasses within the alcohol and of course within the botanicals cell structure, bringing it all to the liquid surface. When the botanical cells are expelling the air, it will also be breaking down the cell structure by forcefully imploding the botanical as much as it can, in turn softening the botanical. It will expel air but of course it will also expel any oils and juices that maybe contained within the botanical. once it all has departed from cells within the botanical it is then ‘infiltrated’ with its surrounding solution (Alcohol). This in turn is speeding up the process required for maceration and vigorously and forcefully extracting flavour and oils ensuring not much is left behind. Oils and flavour compounds leave the botanical and bond with the surrounding alcohol (this is why we macerate), and at the same time the surrounding alcohol aggressively infiltrates the botanical.
We set this video shot up by putting the liquid in a glass vessel inside the chamber so you can visually witness the air expelling during vacuum stages.
After holding vacuum pressure for up to 14-16 hours we then drop the pressure back to normality, all the imploded and deflated botanicals floating on the surface due to the pressure then return to normal shape by inflating which in turn will suck in more of the surrounding alcohol. We then witness most of the botanicals drop to the bottom of the vessel due to no air or gasses left inside for it to suspend or float.
In this video we see the chamber returning back to normal pressure after 16 hours maceration, See how a majority of the botanicals that normally float and sit on the surface drop from the surface to the bottom due to the air being expelled and then them cavities within the botanicals being refilled with its surrounding alcohol.
Analogy Example: Imagine pulling a soapy sponge under water then squeezing it, the pressure from the squeeze will expel all the soapy water and air that it contains (In our case - Flavour and oils), then when you release the pressure from your hand, it will return back to shape replacing the inside mass of the sponge with the surrounding water (in our case more alcohol to bond with any remaining oils, compounds left inside the botanicals).
We find this process also softens and breaks down the cell structure of these hardier botanicals which in turn empowers the alcohol to do its job at penetrating, and getting as much botanical surface contact as possible. Which in turn means more contact with the botanicals oils, fats, tannins, compounds and flavours etc. By being more aggressive & efficient it leaves no stone unturned when it comes to flavour extraction. Leaving us with a full flavoured oily alcohol wash from our hardy botanicals ready for distillation.