Wine has the idea of terroir: soil, climate and terrain together creating a character that cannot be copied.
Aromatics have it too, but almost nobody names it.
The three biggest variables
Altitude. Plants grown high tend to accumulate more esters. With lavender, the share of linalyl acetate rises with altitude, and that is why mountain-grown lavender is valued more highly than lowland lavender.
Strength of sun and amount of rain. Plants under moderate stress tend to accumulate more secondary compounds, because that is a defence mechanism. A moderately dry season can give a denser oil than a season of ideal weather.
Time of harvest. Not only the season but the hour of the day. Jasmine must be picked in step with its species’ rhythm of scent. Arabian jasmine, Jasminum sambac, is most fragrant at night, so it is picked at night or before dawn. The jasmine used in Grasse is a different species, Jasminum grandiflorum, and that one is picked at dawn. Lavender cut early in the morning gives a higher ester share than lavender cut at midday.
Why this matters to buyers
It means that variation between lots is normal and to be expected.
This is a reversal of intuition. In almost every other product category, consistency is a sign of quality. With natural raw materials it is the opposite: a product that stays absolutely stable over many years has either been blended to be uniform, or is not what it claims to be.
The trade-off
If you need a smell that is identical every time you buy — because you make cosmetics for the market, for example — then pure essential oil is not the right choice. What you need is a compounded fragrance, designed precisely to remove variation.
That is not an inferior product. It is a different kind of product, solving a different problem.
Pure essential oil solves the opposite problem: it gives you a slice of one particular season in one particular place. Its value lies in the fact that it does not repeat.
How to read this on an analysis
When you have several analyses of the same oil across several harvests, compare them. Pay attention to the trace components rather than looking only at the two main ones — they vary much more in relative terms, and it is they that carry the marks of region and harvest.