Botanicals and the alchemy of flavor extraction.

[Alchemist75]

So I decided to put this write up together to give finer details on the alchemy of flavor as derived from fruit and herbal extracts. The info provided here will explore a number of particulars with regards to extraction techniques as they relate to flavoring our final products. I apologize for it's length, it's a detailed topic. Maybe pour yourself a glass of your favorite gin or absinthe to sip while you read.

Firstly let's examine distillation of volatile and aromatic components:
Two primary methods exist of distilling aromatics from herbs, steam distillation and simple distillation.
Steam distillation is generally considered to be the best method of procuring essential oils and aromatics from herbs and fruit. The reason this method is preferred is that it has the least damaging effect on delicate phyto compounds and will render them in their native state. Steam distillation works by placing the plant matter into a chamber separate from the main boiler such as your thumper or gin basket. The steam passing from the boiler diffuses through the plant matter carrying with it only the volatile constituents which then pass to the condenser. This method will always produce the best quality aromatic extracts and will have the finest flavor when mixed with ethanolic beverages.
Simple distillation is when the aromatic plant matter is heated directly in the boiler with water or ethanol. This method can change the native characteristics of the volatile constituents in dramatic ways. The direct heat of boiling induces a big variety of chemical reactions that can ruin or potentially benefit the aromas. Oxidization of plant compounds is the most prevalent of changes that can take place in direct heat though others, such as estrification, can occur as well depending on conditions. The flavors that evolve from this chemically altering method can be lighter, burnt tasting, not quite right, improved or simply different than expected. Don't interpret this as being a universally bad thing, in some cases such changes might impart a special something that steam distillation cannot. It's all a matter of direct experimentation as every plant and fruit out there will yield different results.
An additional bit of information on distillation of plant aromatics is that volatile constituents run off not unlike ethanol during its distillation. Aromatic distillates have a head and tail just like ethanol. When you're distilling aromatics the very head of the run will be high in essential oil/aromatic concentration, it will run off cloudy or milky looking typically. As the distillation progresses the essential oil content decreases and the product coming off will steadily grow clear which is the tail. Unlike ethanol, the tail isn't full of nasty tasting compounds though it is very light as where the head is very strong. With steam distillation the tail just kind of fades slowly away though with simple distillation you might actually run into some rather interesting notes as you run deeper and further chemical alteration occurs.
Lastly, not all plants give equal yield of aromatic compounds and you might be surprised at what will or will not distill well. Vanilla is a great example here: that delicious aroma of vanilla cannot be distilled to any measurable extent which is why you will never find a true, non synthetic vanilla essential oil on the market. I've attempted it, I did note a very faint aroma but my attempts to isolate the aroma itself yielded only a very minute amount of precipitate. The aroma of vanilla is really more correctly a flavor arising from resinous compounds found in the beans and must be extracted by very different means which leads us to the next topic.....
Tincturing:
Tincturing is a means of extracting plant constituents in a hydroethanolic solution. In my line of work, tincturing is by far the most common and basic method of producing herbal extracts for therapeutic uses. In terms of it's use in flavor production it opens up whole vistas of possibility and sophistication that the fractional process of distillation cannot. Tinctures draw out a great many different compounds in a single extraction, colors, flavors, aromas, mouth feels, textures and even deeper intoxicating effects. To complicate affairs yet further in this realm is the matter of the proof of the alcohol used to procure the extract. You can tincture everything at a flat 50% abv and get a somewhat broad range of characteristics from a given plant but even then you miss the higher and lower polarity phyto compounds. Those compounds can be big players in terms of flavor and consistency. If you ever examine commercially made tinctures you'll notice that the abv on them will vary greatly from specific extract to specific extract. Each plant has it's specified solvency which draws out the desired qualities. This is a big area of specialized knowledge and long charts exist which provide ideal water/ethanol solvencies, ph ranges, alternative solvents and even ideal temperature. Much of this falls beyond the scope of this website but I have put together a little reference list for your consideration that gives a quick and dirty breakdown of solvency with regards to ethanol, water or the various mixtures of the two:

-Alkaloids: ethanol soluble, 45%-70%, ph will affect solubility
-bitter compounds (sesquiterpene lactones): water soluble, 25% ethanol.
-carbohydrates: water soluble, 25% ethanol, long chain carbs will denature at 45%+ etoh
-enzymes: water soluble, 25% ethanol, will denature at higher proofs, ph may affect activity
-free flavonoids: ethanol soluble, 50%+, extract well in alkaline solutions
-flavonoid glycosides: water soluble, ethanol soluble, when in doubt use 50% etoh
-glycosides: water soluble, 25% ethanol
-gums/mucilage: water soluble, 25% ethanol, precipitates at higher proofs
-lipids: ethanol soluble, use 95% etoh
-minerals: water soluble, 25% ethanol, may precipitate at higher proofs
-naphthoquinones: ethanol soluble but only poorly, use a minimum of 50% etoh preferably higher, completely insoluble in water
-pectins/fiber: water soluble, 25% ethanol, may precipitate at higher proofs
-proanthocyanidins: water soluble, ethanol soluble, more chemically stable in solutions of 50%+ etoh, varying ph can cause them to change color (These are the blues, reds and purples)
-protein: water soluble, 25% ethanol, may denature/precipitate at higher proofs
-resins: ethanol soluble, 80-95% ethanol required, water insoluble
-saponins: water soluble mostly, 25% ethanol, ethanol soluble in some cases
-hydrolizable tannins: water soluble, 25% ethanol, undergo reactions when boiled in water
-condensed tannins: poorly soluble in ethanol, water insoluble
-terpenoids: ethanol soluble at 50%+
-vitamins: water soluble, ethanol soluble, undergo reactions with heat
-waxes: ethanol soluble at 95%

So there's that, it's a general guide but not strictly absolute. Some of the compound classes listed deserve special attention for the distiller. Bitter compounds are not restricted to simply those mentioned above, alkaloids especially can impart an intense bitterness as can some aromatic compounds. Gentian, wormwood and Oregon grape are good examples of bitter herbs fit for flavoring. The proanthocyanidins are all the lovely blues, purples and reds. They are largely flavorless but impart a nice color. Fooling with ph can make those colors change drastically and in pleasing ways. Mucilage is super slimy, it is prevalent in a plants such as marshmallow, slippery elm, cinnamon and others. Cinnamon is a great example of how solvency changes the gummy consistency of an extract: at 50%+ you get the best of cinnamons flavor and deep red hue but extract it below 30% etoh and you end up with a slimy, insoluble, gag inducing mass of blup. See Tosh 2.0 cinnamon challenge. The point here is that if the plant matter is extracted at higher proofs, the gummy mucilage won't come into your liquor but if you try to extract it in stuff you've already cut back watch out. Resins are a pretty important class of compounds flavor wise, roughly as important as essential oils. Resins are usually strong tasting, pungent and aromatic. If you have a lot of resinous compounds in your liquor it will have a waxy mouth feel so less is often more in that department. Resins, like essential oils, are largely water insoluble which means if you soaked your herbs in high proof ethanol they may make things cloud up or even fall completely out of solution when you cut it back. Nonetheless, even after cutting back, the flavor of the resin will linger in your final product, just make sure to decant or filter off any precipitates. This takes us back to my earlier comments about vanilla bean: add it to your spirit before cutting back. It'll give the best flavor at 65-90% ethanol. Tannins impart dryness and can induce an aging effect on your product. Usually tannin rich herbs should be added after cutting the product back. 30%-45% are going to be good extraction ranges here, at 45% especially you'll only get a partial tannin extraction which will keep them from overwhelming the flavor of the booze. Bear in mind that the longer you let the herbs sit in your product, the more and more these compounds will extract. Tannins especially will start to show up after a week or so of soaking.
In terms of preparing water based extracts to cut your liquor back with there are a couple basic rules:
-Light, leafy, flowery and aromatic parts of the plant must be extracted thus: bring a pot of water to a simmer and then take off the heat. Allow it to cool for 5-10 minutes and then put your herbs in. Put a close fitting lid on the pot and allow the herbs to infuse until the liquid cools considerably. Strain the extracted herbs from the broth.
-hard, woody, tough parts, barks and roots generally need to be boiled directly. Put the herb into your pot of water and boil it for about 10 minutes. Cut the heat and allow the plant matter to soak until the broth is cool and strain.
Keep water based extracts in the fridge until you're ready to use them.
Finally, another important thing to consider when selecting botanicals is whether they are fresh or dried. The drying process with plants can drastically alter the flavor of the compounds present. Oxidization, enzymatic action and evaporation of aromatic compounds will definitely change things. In many cases the changes aren't detrimental but in some they are. Lemon balm is a great example of what drying can do to the aroma profile. If used fresh, lemon balm will have a rich, sweet, lemony aroma and flavor. Dried, it loses much of this aroma and will only impart a light flavor at best. Rose petals have this problem as well. Usually, using herbs fresh is where it's at but often the fresh herbs are not available so you must make due with what you can find. If tincturing a fresh herb for flavors common wisdom is to let it soak in 95% ethanol. The reason for this is that there is already much water in the plant and it's juices will be entrained by the pure ethanol. Usually after tincturing fresh plant material the final proof will end up in the 50-60% range so the liquor will already be cut back considerably.
Oh, and, always use organic botanicals when and where available, distillation of aromas especially can concentrate pesticides which is no good.

Long post, I hope you survived it, comments and questions are very welcome as always.
Cheers!