Kochii is one of the West Australian oil mallees, a small, scrubby, multi-stemmed eucalypt from the dry country east of Perth. It is not much to look at and it was never a forestry tree. Its story is not about timber or even really about perfume. It is about salt, and about a plant that got asked to hold a landscape together and turned out to carry the cleanest eucalyptus oil going.
The name
Kochii is named for Max Koch, the collector who gathered the plant in the field. The doubled i is not a typo and not a botanical flourish: it is just what Latin does to a surname that ends in a consonant when it is turned into a name. Koch becomes kochii. The shop spelling with two i's is the correct one, and worth getting right, because a single i points at a different word entirely.
A tree with a job
To understand why kochii was planted at all, you have to start with what went wrong in the wheatbelt. Across the last century, huge areas of West Australian farmland were cleared of their native scrub and put down to crops and pasture. The scrub had been doing quiet work: its deep roots drank the rain before it could sink far. Take the scrub away and the water table rises, and as it rises it dissolves and carries up the salt that had been sitting harmlessly in the soil for a very long time. The salt reaches the surface, the ground turns white and sour, and the paddock stops growing anything.
The fix that emerged was to put deep-rooted native mallees back into the farmland, planted in belts through and around the crops so their roots could pull the water table back down. Oil mallees like kochii were ideal for it: hardy, salt-tolerant, happy in poor ground, and coppiceable, so a farmer could cut the tops for a return without killing the planting. The eucalyptus oil is a co-product of a plant that is really there to manage water. The oil pays part of the way for a tree doing a much larger job.
That is an unusual thing to be able to say about an essential oil. Most of them come from a crop grown to be a crop. Kochii oil comes, in large part, from a plant put in the ground to stop farmland turning to salt.
Why the number is so high
1,8-cineole, also called eucalyptol, is the compound that gives eucalyptus oil its cold, clearing character, and it is the figure a pharmacopoeia actually measures. A high, stable cineole reading is what separates a eucalypt worth distilling from one that is merely pleasant. Blue gum usually gets over the line. Blue mallee sits comfortably above it. Kochii sits higher again, up near the ceiling of what the genus produces.
There is a fair amount of variation inside the name. Kochii covers more than one subspecies, and their oil is not identical, so the exact figure moves a little from one planting and one distillation to the next. What holds across the commercial West Australian material is that it is very cineole-rich, comfortably in the mid-to-high nineties, which is why it gets reached for whenever the point of the oil is potency and a clean, uncluttered profile rather than nuance.
An oil that is a by-product of holding a landscape together, and still ends up carrying more of the active compound than almost anything else in the genus.
How it smells
You can tell a high-cineole oil the moment you open it. Kochii is sharp, cold and clean, minty at the very top, with very little of the soft, sweet, camphorous roundness that makes blue gum feel familiar and comforting. It is the most surgical of the three eucalypts in the range: less character, more clarity, the note pared back to almost nothing but that clearing coldness. Where blue gum is the one that smells like childhood chest rub, kochii is the one you reach for when you simply want the air in a room to change.
The usual cautions apply, and they are the ones that apply to all the cineole-heavy eucalypts. Dilute it well, keep it away from the faces of babies and young children, and check with a practitioner first if asthma is a factor. Treated with a little respect it is one of the most efficient things in the cupboard for clearing a stuffy head and a stale room.