Plant Distillation Techniques
Essential Oils and Steam distillation By Jill Mulvaney
What is “Essential Oil” When I think about this, I sigh – and stare out the window at the birds on the tree, essential oils, such an enigma. Wikipedia describes them as “a concentrated hydrophobic liquid containing volatile aroma compounds from plants”, a pragmatic answer – a concentrated substance that is repelled from a mass of water (hydrophobic) that has smell or odour (aroma compounds). Apparently they are “essential” as well! When I’m out walking, I see and feel a plant, reach out and pick a leaf or flower, crush it in my palms, cup my hands, cover my mouth and nose and deeply inhale. The plant and I begin our conversation. We use the silent language of aroma and sensation. How I wish I could translate all that into academic words that make sense, but I have learnt to trust that the plant shares information with each aromatic conversation conducted with mindful body awareness and sensitivity. So maybe it is the soul part of the nature of plants that can speak. Aroma is certainly a powerful conduit of subtle change, response and reaction. Essential oils are aroma. To be able to steam distil plants I have found or grown myself has been a profound experience. Even though the process is quite simple, you become part of a magical alchemy of transformation. The energy of steam changes the chemistry of a plant so that its constituents are released into liquefied steam. That in itself is enough, however then, that liquid releases millions of tiny bubbles of aromatic essential oil. It is lighter than water so floats to the surface and here gathers the volatile aromatics – the essential soul of the plant.
The Process of Steam Distillation Steam distillation is mostly used to produce essential oils. The plant material is subjected to steam under pressure. It does not come into contact with the boiling water. Water boils at 100°C, steam has a higher temperature than boiling water; a steam scald is worse than a scald from boiling water.
Distilling for Essential Oil by Steam Distillation I’m going to use Rosemary again as I’m taking up where I left off in my last article in the Winter Avena issue Hydrosols and Hydrodistillation. I hope I can illustrate the difference between the two distillation methods and the difference in the hydrosols produced. I use a Copper Alembic Column Still for steam distillation, the only difference between this and the one I used for hydro-distillation – the Traditional Alembic Pot Still, is that it has a Column that sits on the pot with a sieve plate at the bottom. The herb is placed in the column; the column is placed on top of the pot of boiling water. The sieve plate keeps the herb material above the water so only steam comes into contact with it.
1. I have my Column Still
set up in a sheltered spot in the garden. I have already cleaned it by distilling rye flour slurry. To do this I mix 450g of Rye Flour in 4 L of water and pour into the pot. I assemble the whole still and heat the rye flour mix until it boils. It becomes frothy and seeps out the joins. Once it comes out of the condenser bucket as distillate, I turn the heat off. When the Still is cool enough to handle, I dismantle it and scour it with Eco Cream Cleanser (it contains a citrus oil that cleans the copper). I rinse and dry it thoroughly, leaving it in the sun to finish the drying process. Before I start a new distillation I always distil hot water to check the distillate is tasteless, odourless and clear. I know I have a clean still.
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Plant Distillation Techniques
2. The pot is 2/3 filled with water and placed on a gas ring
to bring the water to the boil. It’s important to have everything at hand for a distillation. I have my water pump on keeping a steady flow of cold water running through the condenser bucket, my sterile beakers and oil separators are ready to collect the distillate. I have a bowl of rye flour paste to seal the joins in my still so I don’t lose precious steam.
3. And of course I have harvested and prepared my herb. The leaves and flowers have been stripped from the stems of the Rosemary and sit fragrantly waiting. It is the same harvest I used for the hydro-distillation
4. I place five good handfuls of rosemary into the column. When the water in the pot is boiling, I carefully remove the onion dome and sit the column on the pot making sure it is square. I place the onion dome on the column, checking its level. Because the Rosemary is cold I have a little time before the steam works its way through.
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AVENA Journal of the New Zealand Association of Medical Herbalists Spring 2012
Plant Distillation Techniques
5. I work quickly now. If I lose any steam, I will lose precious essential
oil. I quickly but carefully seal the join between the column and the pot and the column and the onion dome with the rye flour paste. As the copper heats it bakes it dry and seals the joins. By the time I have done this, the onion dome is hot which means the steam has spiralled up the column, the heat burst open the cells of the plant and the volatile oils released and carried in the steam. The steam spirals in the onion dome, any particles of dust of physical matter falls back. The steam flows down the bird’s beak, through the connecting pipe and into the condenser coil.
6. Just as in the hydro distillation, it is vital to have a steady stream
of cool water runing around the condenser coil throughout the whole distillation. Actually it is even more important when distilling with steam, it’s a hotter faster distillation. The water needs to be boiling vigorously to create a good body of steam under pressure to burst the cellulose of the plants to release the essentail oil. The distillate will flow faster than a hydro distillation. The essential oil will be released in the first 200ml of distillate.
7. On a 10 L still I collect 500ml of Hydrosol. The oil has been expelled
from the mass of water and floats to the top. The hydrosol is not as milky as in a hydro distillation and of course there is significantly more oil released. The aroma is stronger, sharper and more intense. I check the pH. Depending on my purpose I may continue distilling for hydrosol. There will be very little oil in the next 500ml but often the hydrosol is still of a good aroma, flavour and pH. As soon as the pH increases I stop the distillation.
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Plant Distillation Techniques
8. This is the best part! These
are my oil separators. One is 500ml and other 60ml. They both sit in rings and are clamped onto a retort stand. I use the larger separator when distilling botanicals that will yield between 3-10ml of oil on 500ml - Rosemary, Eucalyptus, Lavender, Clary sage, Manuka, Thyme, Peppermint……. The smaller one is to collect precious drops – Rose Geranium, Melissa, Rose, Lemon Verbena, Chamomiles, Yarrow…..
9. I pour the hydrosol into my large oil separator. As I do this, the oil
is mixed with the hydrosol again. I watch in awe as it settles. Millions of miniscule bubbles stream to the surface. They are tiny drops of essential oil that the water has released like a sponge being squeezed. The oil collects at the top, often a golden colour. The hydrosol settles and clears. At this stage I’m aware of the energetic lively nature of this process and feel a deep sense of respect and awe.
10.
A clean beaker is placed at the bottom of the oil separator. I carefully turn on the tap to release the hydrosol watching carefully to turn off as the oil collects at the bottom once the hydrosol has been released! There, now I have my reward, 3ml of precious essential oil! I will need to distil another 3 times to get my 10mls! However I will also have 2 litres of fragrant Rosemary hydrosol.
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Plant Distillation Techniques
11. There is moisture still in the mix. I don’t want to leave it in as it may cause a
bacterial growth and degrade my oil. I put my test tube with the oil in the freezer. This dries the oil out and freezes any moisture. I pour the oil off into an amber dripulator bottle. It goes into my precious collection of my own distilled essential oils. By this time next year I hope to have 25 of my own distilled oils. I already have 50ml Eucalyptus, 50 ml Peppermint Eucalyptus, 10 ml Rosemary, 3 ml Lemon Verbena, 10 ml Lime, 10 ml Manuka 10ml Ginger and 10ml Thyme In spring I will be harvesting German Chamomile, Rosemary before flowering, Orange, Grapefruit & Lime flowers, spring Manuka and Kanuka, Tarata, Rose Geranium, Bay leaves, Melissa. In summer it will be Lavender, Clary sage, Lemon Verbena, Basil, Peppermint, Helioscrysum, Yarrow, Angelica and some trimming of the citrus as the fruits form tiny balls – for Petitgrain. That’s enough!
Table 1 Hydro-Distillation
Steam-Distillation
Plant is subjected to boiling water
Plant is subjected to pressure and steam
Distillation is slower and cooler
Distillation is fast and hot
Hydrosol is often milky
Hydrosol is mostly clear
The distillate shows little essential oil floating on the surface, most remains in suspension
Essential oil is evident on top of the hydrosol and is removed.
Aroma is complex as are the flavours
When the oil has been removed, the aroma of the hydrosol is light and delicate, the flavour less intense
Nothing has been separated from the distillate – it remains complete
Has a dual result – Essential oil and the Hydrosol, however the hydrosol has lost an element – the essential oil
Every distillation is different depending on season, soil, and climate. This table is an approximate guide to volume’s and quantities. An idea of plant volume – 3 mature Lavender augustifolia harvested – flowering tops weighs 1kg approx. Lavender is a high yielding plant. 1kg of flowers yields approx 25-30ml of oil. Most other plants I distil yield a quarter to half that amount.
Table 2 Size
Plant Quantity
Lavandula angustifolia
Approx. ess. oil yield
Hydrosol yield
5 L column
250g or 2-3 handfuls
1 mature plant – flowering tops
1-2ml
250-400ml
10 L column
500g or 5-6 handfuls
1.5-2 mature plants
3-5ml
500-1.5 L
20 L column
1.5 – 2 KG
4-6 mature plants
5-15ml
3-5 L
40 L column
5 KG
8-10 mature plants
20-50ml
5-10 L
150 L column
20-30KG
60-90 mature plants
200-500ml
20-50 L
ABOUT THE AUTHOR: Jill currently resides on Waiheke Island with her partner Charlie. Together they run distillation workshops and demonstrations throughout New Zealand and sell alembic stills worldwide. Go to their website for more information, to purchase an alembic still or see if there's a workshop coming to your town soon!
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