Soxhlet


	We described the Soxhlet extractor on page 110 of The Compleat Distiller, but have found that many people find its operation difficult to envisage. We hope that this animation of the device will help solve that, and give you a much better idea of what is going on.

First of all, it should be made clear that a Soxhlet is used for extracting resins, heavy oils and resinoids, none of which are particularly volatile and so are not susceptible to extraction by steaming. These substances are best extracted by soaking in a solvent, and a Soxhlet is simply a device that does this with great efficiency.

As you can see, the solvent is heated in the boiler at the bottom, and the pure vapor rises up through the bypass tube and into the top part of the Soxhlet container. The vapor continues to rise until it meets the cold condenser, then the liquid drips back down into the thimble that holds the material we want to extract from. This thimble is porous, so it not only holds the solid material, like seeds or berries, but also acts as a filter so that the this material doesn't clog the siphon tube. When the level of the liquid in the Soxhlet container reaches the same level as the top of the siphon, then the liquid containing dissolved compounds is siphoned back into the boiler.

You can see that the level of liquid in the thimble doesn't fall as quickly as the level of the liquid surrounding it, as the liquid in the thimble has to soak out of the porous sides, and this only happens when the level of the liquid in the container falls below the level in the thimble.

The end result is that the material in the thimble is subjected to repeated soaking in pure solvent, and this is much more efficient than continuously soaking it in a solvent that steadily increases in concentration of the extracted compounds.

We have given this matter a great deal of thought, and it is our view that there should be no reason at all why you may not use solvents like ethanol, even in places where distillation of ethanol is subject to regulation. Where such regulations exist, "distillation" is usually interpreted to specifically mean the concentration and external collection of ethanol for use in other applications. This even includes extraction of ethanol from a solution where it has been used in a process as a solvent, in order to save it for use later as a solvent in another extraction. The logic behind this little "gem" of legislation is hard to fathom, as it is equivalent to saying that you may use a bread knife only once to cut a loaf, then you must throw it away and buy another!

In contrast, as all the ethanol contained in a Soxhlet merely circulates within the device and is continuously returned to the boiler/collection vessel to form a solution with exactly the same concentration of ethanol as before, the end result is exactly the same as if you simply soaked the seeds, berries, etc in ethanol or a water/ethanol mix with no distillation at all - no different to putting an olive in a martini, or laying down a few jars of ginger in whiskey or cherries in brandy to make nice Christmas presents!

HOWEVER .... be warned! The bureaucratic mind is not restricted by mere logic!
In Australia, for example, where almost the whole of the central region is desert, it is illegal to operate a water still with a boiler larger than 5 liters! One wonders if this bit of odd legislation led to the partiality that many Australians have for a "cold tinnie" of beer!

Of course, you could always take a pot and boil the plant material in a water/ethanol mix (vodka, or even wine if you want the flavors from that as well!) and let the vapor go to atmosphere. You will achieve some extraction, albeit not as efficiently as with a Soxhlet, and will be able to strain off the remaining liquid to save the dissolved compounds. This is definitely, positively legal, and cooks do it every day in every country of the world. Note that condensing the vapor from the pot would be against the regulations that hold in some countries, although these same regulations are silent on what to do about vapor that condenses on a lid! Also note that any condensed vapor will only contain those compounds that are volatile, and those would be best extracted by steaming. Do not confuse materials that are volatile with those that are not!

In his method for making gin essence (see the page on Flavors), Mike Pemberton uses a coffee pot to boil his plant materials and condenses the vapor in order to collect the volatile compounds. What he is doing is steam distillation, and by adding a bit of ethanol to his initial mix he is simply helping the extraction of those volatile compounds from the plant matrix. However, he lives in New Zealand, and doesn't have to worry about silly regulations relating to use of ethanol! He has also made himself a very efficient Soxhlet out of readily available plumbing parts, and uses this whenever he wants to extract non-volatile compounds from small quantities of material, such as caraway seeds, anise, etc.

If you want to have a final solution that is much stronger than you can get even by using a Soxhlet, then the simple answer lies in remembering why it is that you are using this form of extraction in the first place. It is to extract compounds that are not volatile. You can therefore take the solution you get and, if it is too dilute for your needs, subject it to simple evaporation. You will lose to the atmosphere any liquid solvent you have used, but not the low volatility compounds. You can then safely add legally purchased 95% ethanol (Everclear) to make up a tincture that will preserve and carry the extracts.

So there, for what they are worth, are the regulations that apply in some countries. If you think they should be amended in order to make more sense, strive to get them changed. Until they are, live by them!