Extraction methods · Comparison
Nine methods, side by side
Each method page covers one method in detail. This page puts all nine on the same plane, along the four axes that decide the choice when you have to pick a method for a particular raw material.
The temperature axis
Heat is the most important variable, because it decides which molecules survive. The axis below ranks the nine methods by the highest temperature the raw material has to endure.
Four axes side by side
| Method | Heat | Solvent | What it loses | Suited to | The product is called |
|---|---|---|---|---|---|
| Water distillation | 100 °C | no | Esters, through hydrolysis during long immersion in boiling water. The whole group of compounds heavier than about three hundred mass units. | Heat-tolerant leaves and stems: lemongrass, cajuput, mint, star anise. Also suits powdery materials that compact easily. | Essential oil · Hydrosol |
| Water and steam distillation | 100 °C | no | Heavy compounds, and some esters, though fewer than in water distillation. | The same materials as water distillation, at medium scale. | Essential oil · Hydrosol |
| Direct steam distillation | 100 °C | no | Compounds heavier than about three hundred mass units, and fragile molecules that cannot withstand heat. | Most heat-tolerant leaves, stems, peels and seeds, at industrial scale. | Essential oil · Hydrosol |
| Cold pressing | 25 °C | no | Nothing is lost to heat. But the photosensitising compounds cannot be removed either. | Citrus peel only. It cannot be used for any other material. | Cold-pressed oil |
| Solvent extraction | 50 °C | yes | Very little compared with distillation, but not nothing. The first loss is purity: there is always trace solvent at parts-per-million level. The second is in the last step — when the alcohol is driven off to obtain the absolute, the most volatile part goes with it. That is why some perfumers prefer concrete to absolute for a few materials. | Flowers that cannot stand heat: jasmine, tuberose, orange blossom, mimosa. And dry plant resins. | Concrete · Absolute · Resinoid · Oleoresin |
| Supercritical CO₂ | 40 °C | CO₂ | Very little. This is the method that keeps the most, including compounds that distillation destroys. | Almost any material, but the equipment is very expensive. | CO₂ extract |
| Enfleurage | 25 °C | yes | Nothing is lost to heat, but two things are lost depending on where you stop. Stop at the pomade and you lose only time and labour: one batch needs weeks and dozens of flower changes. Go on to the absolute and you also lose the lightest part, which leaves with the alcohol when the solvent is driven off — as in every process that yields an absolute. In addition, fat does not absorb every group equally: it favours lipophilic molecules, so more polar groups enter poorly. | Flowers that keep giving off scent after picking: jasmine, tuberose. Pointless for flowers that stop as soon as they are picked. | Pomade · Enfleurage absolute |
| Hot maceration | 60 °C | no | The lightest compounds, because of moderate heat and long times. It cannot capture compounds that do not dissolve in oil. | Flowers and herbs in craft production, when no equipment is available. | Infused oil |
| Tea scenting | 45 °C | no | The lightest part of the flower, lost in each drying. And it yields no concentrated form to blend into other products. | Flowers that keep giving off scent after picking, with dry carriers that absorb smell. Mainly lotus and jasmine. | Scented tea |
The heat column gives the highest temperature the raw material has to endure, as a representative point rather than an operating range. Tea scenting shows 45 degrees because of the tea-drying step between scentings, not because there is heat during scenting.
The solvent column separates two things that are often lumped together. A solvent is a liquid added to dissolve the aromatic part and then removed from the final product — hexane, alcohol, CO₂. A carrier holds the aromatic part and stays in the product — the base oil in maceration, the tea leaves in tea scenting, the fat in enfleurage.
Enfleurage shows “yes” because the last step is an alcohol wash. If it stops at the pomade, no solvent has been used — that line coincides exactly with the line between the two product names.
Three things that show up side by side
There is no best method. CO₂ extraction keeps the most, but the equipment is so expensive that most raw materials are not worth the investment. Cold pressing loses nothing to heat, but works only for citrus peel. Each method exists because it suits a particular group of raw materials and a particular scale.
All three distillations run at 100 degrees, but they are not the same. The identical temperature hides the real difference: whether or not the raw material sits in boiling water. That is why the temperature axis alone is not enough to choose a method.
Solvent-free does not mean better. Distillation uses no solvent but destroys more molecules than solvent extraction. For jasmine, the “cleaner” method gives a much worse product.
How to choose
The first question is not which method is best but how much heat the raw material can take.
If it can: distillation, choosing among the three by investment and acceptable batch variation. If it cannot: solvent or CO₂ extraction, choosing by whether you accept trace solvent. If it is citrus peel: cold pressing — there is no other option.
Once you know which method you use, read what the words on the label mean to name your product correctly.