Looking at an analysis, the eye goes automatically to the two or three lines with the largest percentages. It is a natural reflex, and it misses the most interesting part.
Two different roles
Main components establish the type. A sample in which linalool and linalyl acetate make up seventy per cent is lavender. That figure answers the question what is this.
Trace components establish the character. The thirty other compounds, each under one per cent, answer the question which bottle is this. They carry the marks of the land, the season, the time of harvest.
That is why two lots of lavender, both seventy per cent in the two main compounds, still smell different.
Why they vary more
Main components are made by the plant through stable metabolic pathways, so their proportions are fairly steady from harvest to harvest.
Trace components are often by-products or the products of secondary pathways, which are much more sensitive to stress, temperature and timing. They can double between two harvests while the main components move only a few per cent.
On the example page, the 1,8-Cineole row goes from 0.9 to 2.0 across six harvests — more than doubling. Over the same harvests linalyl acetate varies only within a narrow range.
Three things trace components can do
Identify a group of species. A few compounds are found almost only in one genus. Lavandulyl acetate is found almost only in the genus Lavandula, so its absence from a sample labelled lavender is a sign worth questioning.
But note the scope: it points to the genus, not the species. Lavandin is also Lavandula and also contains it. An indicator answers only the question it was designed to answer.
Detect blending. Blended goods are usually poor in trace components, because the blender cares only about the peaks listed in the standard.
Read the age of a bottle. The ratio of caryophyllene oxide to beta-caryophyllene rises steadily over time, because the latter oxidises into the former.
How to reread an analysis
Next time you hold one, do the opposite of the reflex: read from the bottom up.
Start with the smallest lines. Count how many lines are under one per cent. Look for whether the species’ marker compound is present.
Only then look at the two largest lines — and by then they merely confirm what you already know.