The two measurements that decide a batch
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Two numbers describe a spice more usefully than any adjective. One you will buy against and never measure. One you can and should measure every week.
Volatile oil: what it is and who measures it
The percentage of essential oil in the material, determined by steam distillation. It is the trade's quality measure and ASTA publishes a minimum per spice, with black pepper, cinnamon and oregano often quoted.
It is a laboratory method. You will not run it. You will ask for it, buy against it, and keep the figure with the lot record.
Moisture: the one you can act on
Spices are graded on moisture because high moisture causes clumping, spoilage and shortened shelf life. Unlike volatile oil, this one moves under your control: it is affected by your store, your packing room and your closure.
The working threshold is the room rather than the material. Above roughly 55 to 60 percent relative humidity there is enough vapor to form liquid bridges between particles, which is where caking begins.
What you can measure yourself
A hygrometer in the packing room and the store, which tells you whether today is a filling day and whether your storage is doing its job. This is the highest-value instrument in a small spice operation and it costs less than a case of jars.
A scale to a tenth of a gram, for fill weights and for the packaging test: weigh filled jars, store them in different conditions, and weigh again at four and twelve weeks. Weight gain is water coming through your closure.
And your nose, against a sealed reference sample kept cold. Unscientific, free, and the thing that actually catches a declining supplier.
Reading a certificate of analysis
Look for four things: the ASTA cleanliness statement, the volatile oil percentage, the treatment method, and the lot and origin. A certificate with a price and a product name on it is a delivery note wearing a better title.
File it with the lot. The moment it matters is a moment when producing it quickly is the entire point.