{ Vanilla oleoresin – hexane extract }

In this first attempt I tried to extract the aromatic principles of roughly 0,5 kg Bourbon vanilla beans (from Madagascar) by hydrocarbon percolation. For this purpose I used n-hexane Scharlau 95% (120 euros 5 L canister). The extraction product is called an “oleoresin” (resinoid or concrète) because it carries a volatile fraction and odorless waxes and resins (I suggest you to read S. Arctander’s monograph on this subject: Vanilla oleoresin).

I bought extraction grade vanilla beans: water content is kept low.

I was quite satisfied with the overall “standard” odor quality of the starting material: “senza infamia e senza lode” (nor too bad nor too good). I only perceived a faint fermented type, volatile off-note when unpacking the beans. Apparently it was distilled off when evaporating the solvent, since it is not detectable in the oleoresin anymore (when disassembling the Soxhlet extractor after the process I was able to smell an acetic acid-like note on the top of the Dimroth condenser, while the recovered hexane did not carry such note).

In this first photo you can see the Soxhlet type apparatus I’ve set up for the extraction process:

Soxhlet apparatus

Soxhlet apparatus

Here’s a video of the soxhlet extraction process:

Comminuted Bourbon vanilla beans before extraction:

comminuted vanilla beans

comminuted vanilla beans

Comparison between exhausted (left) and fresh (right) vanilla beans. From this photo you can guess the extractive power of hexane: the vanilla on the left is drier and paler in color. It still carries some aromatic principles (not hydrocarbon-soluble material I presume).

exhausted (left) fresh comminuted vanilla beans (right)

exhausted (left) fresh (right) comminuted vanilla beans

A Soxhlet apparatus is designed in order to recirculate the solvent throughout the botanical material. The temperature at which the extract is exposed is the boiling temp. of the solvent used. At standard pressure n-hexane boils at 68° C (relatively low). The raw material is not directly in contact with the boiling solvent, thus preserving it a little bit from excessive heating.

In this first attempt I let the solvent recirculate 6 times (2 hours refluxing). The first run is, not surprisingly, the most charged with volatile materials, waxes and pigments (it is the darkest in color). The fourth is almost colorless.

I let the extraction liquor stand for a day and then filtered under gentle vacuum. This process results in a small loss of solvent. n-hexane is very volatile and vapors arise easily from the filter paper. It is the most troublesome phase of the process, when you are in strict contact with the solvent. I carried out this operation on the outside avoiding breathing too much vapors.

vacuum filtration

vacuum filtration

I then evaporated the solvent under vacuum (pressure between 150-300 millibar) at ~30° C. It is really tricky to evaporate all the solvent. The last traces are the most difficult to eliminate: the temperature increases and there is the risk of spoiling the extract.

recovered solvent (left) vanilla oleoresin (right)

recovered solvent (left) vanilla oleoresin (right)

A video I recorded of the evaporation process:

A rotatory evaporator would give better results: solvent recovery would be faster and more efficient.

I used a water vacuum pump: I can reach a pressure as low as 8 millibar, but in normal working conditions (heat, arising vapors) it is stable at around 150-200 millibar. A membrane pump would be more reliable.

An ice trap would also improve solvent recovery and avoid vapor leakage in the air (I used a Dimroth condenser and recovery was very good, I registered only minor losses through the vacuum pump).

The yield was quite good: 31 g oleoresin from 471 g of crude vanilla beans (6.7%). I was able to recover most of the solvent (major losses were due to filtration and adhering solvent on exhausted vanilla).

Vanilla oleoresin is a viscous, dark brown liquid not completely alcohol-soluble. It possesses a true-to-nature, rich and creamy vanilla aroma, with woody and licorice undertones and a tobacco nuance. It is not as powerful as a vanilla absolute, since it still contains odorless waxes and non-volatile material, but it possesses good tenacity.

I don’t appreciate headnotes from this oleoresin very much: they are quite smoky-bitter, overly sweet to my nose. It may be a factor of concentration (too high to fully appreciate the extract) or there could be solvent traces (a gassy nuance? Not quite sure). I assume that during solvent recovery the temperature increased too much in the last minutes (bitter, smoky, burnt odor detected?).

An hydrocarbon extraction followed by an hydro-alcoholic one should give better results: not complete alcohol solubility, but a much more complex and rich aroma quality.

Tightly controlling the temperature is essential to achieve satisfactory odor quality.

    • bitelgius said:

      thanks for appreciating my work

      • Carole said:

        I am really impressed by all your work and your posting. You must be a chemist? Is there any ingredient someone might use to sabotage my perfume? I mean deliberately adding something that can ruin it? Thank you.

        • andrea said:

          Hi, why would you want to ruin your perfume?

          • Carole said:

            Hi, I was just wondering of someone else could be sabotaging mine with a chemical?.

          • andrea said:

            Yes, adding anything that is not part of the original formula. But if I think that it is quite unlikely…
            You should check the crimp cap if it has any sign of tampering.
            However if the bottle has a screw cap you can only detect a ‘sabotage’ by nose, or by gc-ms.
            If I was to cut a perfume I would use an odorless solvent, like DPG or ethyl alcohol. In that case a 20-30% cutting (not so much profitable) should be quite obvious to your nose (decreased volatility -DPG- and a weaker odor in general). In the case of other -odourant- chemicals the fraud is much more evident: the formula is unbalanced, with too much emphasis on a certain note. If the purpose was to completely ruin your perfume I would choose powerful bad-smelling chemicals, like some pyrazines or sulfurous molecules (rotten eggs, sweat, urine-like odours). And all these are some quite safe ways to sabotage a perfume.

          • Carole said:

            That is very helpful and thank you for you prompt and thorough reply..I will keep you posted. Carole

  1. Jori said:

    Hi. I was wondering if you have experience with achieving the same results, but only using a rotovap machine? If so, would you suggest adding the plant materials with the hexane to the rotating flask and pull off the hexane and concentrate the plant oils in the rotating flask and then add ethanol to the plant material and resins left in the rotating flask to extract the final scent? OR, would I add the hexane ti the plant materials, pull off the hexane, then discard the plant materials and add the hexane back to the rotating flask and again pull off the hexane to achieve a resin in the rotting flask that is then diluted with ethanol to extract the final scent?

    I am curious about portions as well. How much hexane would one add to how much plant or seed material? I am just gutting started with playing around with hexane and must admit, I am a little nervous.

    My end result is to have notes from plant material so making scents and edible scents.

    I would greatly appreciate your thoughts.

    • Andrea said:

      Hi Jori,

      A rotavap is used only to evaporate the solvent from the extraction product (resinoid or ‘concrète’, free from any plant material). It is a more efficient and elegant way to pull off the solvent than the one I described above.
      Sadly I don’t have a rotavap at home, but I use the machine at the university labs at times.

      I don’t understand if you are saying that you would extract your plant materials directly into the rotavap.

      In order to extract the plant material you shouldn’t use the rotavap, but one of the following setups (I assume that, if you have a rotavap on hand you should be able to find any glassware):

      -A simple refluxing apparatus, that is good for materials that are not heat-sensitive (if you are using hexane note that the temperature in the still pot is constantly at 68° C).

      -A Soxhlet extractor, which is always a better choice than a refluxing setup, especially for materials that are quite sensitive to heat. However, the main drawback is that the solvent charged with the resins/waxes and oils from the plant is constantly exposed to the heat in the still pot.

      -Simply soak the plant material in the solvent in a flask, keeping a constant stirring and low temperatures (like a cold bath). Soaking can take from 30 minutes up to a few hours. This is a very simple solution but effective for fragile plant materials (like flowers).

      Then, cool down and filter the mixture solvent-resins/waxes-oils in order to free the solution from any solid plant material or organic insoluble residue.

      Now you can pull off the solvent in the rotavap. You have obtained what is called a resinoid or a ‘concrète’ (depending on the starting material).

      In order to make this product alcohol-soluble (thus obtaining what is called an ‘absolute’), and remove odourless material (resin, wax) and concentrate the odour you wash your resinoid/concrète with 95°/190 proof ethanol. You then filter again and pull off the ethyl alcohol by means of the rotavap.

      About proportions: it really depends on the starting material. As a general rule: you should add as much solvent as it is needed to completely soak the product. It doesn’t condition very much the final result, but be careful: the more solvent you use, the more you have to pull off.

      Above all, be careful. As a reminder: as you know Hexane is highly flammable and can form explosive vapours with air. Do not use any flame to heat your still flask. Double-check you glassware before using checking for cracks.

      Please note: do not use the product you’ll obtain for food unless you are completely sure there is no trace of hexane left.

      If you have any further questions I’ll be glad to help you!

  2. megan said:

    Do you sell your vanilla oleoresin?

    • Andrea said:

      No, I am sorry.

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