A certificate of analysis is only as useful as the buyer's ability to read it. This is a working guide to the tests that appear on certificates for dried herbs and spices: what each one measures, what it can prove, and what it cannot.
One principle underlies all of it. A test result describes the sample that was tested. Whether it also describes the twenty tonnes in the container depends entirely on how that sample was drawn — which is why sampling deserves as much contractual attention as the analysis itself.
Physical parameters
Moisture
Usually determined by loss on drying under defined conditions, sometimes by Karl Fischer titration where precision matters. Moisture is the most operationally important number on most certificates because it predicts behaviour: material above a safe level supports mould growth, cakes in the bag, and loses quality across a voyage. It is also the parameter most affected by conditions after analysis, so ask when and where it was measured.
Purity and foreign matter
A physical separation and weighing of the fraction that is not the target material. The number is only comparable between suppliers when the definitions match: some count other plant parts of the same species as foreign matter, some do not. Ask what is included in the impurity fraction before comparing two "99%" offers.
Total ash and acid-insoluble ash
Total ash is the residue after incineration — the mineral content. Acid-insoluble ash is the fraction of that residue that will not dissolve in acid, which is essentially silica: sand and soil. A high acid-insoluble ash figure is the classic signature of inadequate cleaning, and it is a more reliable indicator of processing discipline than a visual inspection.
Bulk density and particle size
Relevant where the material is dosed by volume or blended. For cut and sifted material, a screen-based particle size distribution is a more meaningful specification than a nominal cut description.
Aroma and active constituents
Volatile oil content
Determined by steam distillation with volumetric measurement. This is the parameter most closely related to sensory strength in aromatic herbs and seeds, and the one worth making contractual if your product's flavour depends on it. Volatile oil declines with age, grinding and poor storage, so a lot-specific and recent figure is worth considerably more than a typical value in a brochure.
Chromatographic profile
Gas chromatography separates and quantifies the individual constituents of the volatile oil. It answers questions a total-oil figure cannot: whether the profile is characteristic of the species, and whether it has been adulterated or diluted. Reserved for high-value materials and authenticity questions, because it costs more.
Microbiological testing
Dried botanicals are agricultural products dried in open air; they carry a natural microbial load. The tests that normally appear are total plate count, yeast and mould, Enterobacteriaceae or coliforms as hygiene indicators, and pathogen testing — most commonly Salmonella, expressed as absence in a stated sample mass.
Two things buyers should understand:
- Pathogen absence is a probability statement, not a guarantee. "Absent in 25 g" means it was not detected in the portions examined. Larger sample masses raise confidence and cost.
- Acceptance criteria depend on the application. Material going into a product with a validated heat step is judged differently from material going into a ready-to-eat product. Specify against your use.
Where a specification cannot be met by cleaning alone, a validated microbial reduction treatment may be applied. Treatments differ in their acceptability between markets and customers — steam treatment, irradiation and fumigation are not interchangeable from a labelling or market-acceptance point of view. If your customer or market prohibits a treatment, say so before contracting.
Chemical contaminants
Pesticide residues
Multi-residue screening by GC-MS/MS and LC-MS/MS covers a broad panel of active substances. Maximum residue levels are set by the destination market and are revised, so a compliant result is compliance against a stated framework on a stated date. Name the framework in the contract — the EU, the US, or another — rather than writing "compliant with international standards", which is not a testable term.
Heavy metals
Lead, cadmium, mercury and arsenic, typically by ICP-MS. Uptake relates to soil and water, so results are origin- and lot-related rather than a supplier's choice.
Mycotoxins
Aflatoxins and, for some commodities, ochratoxin A. These are the consequence of mould growth in the field, during drying, or in storage — which is why moisture control is the primary preventive measure and testing is the verification, not the control.
Authenticity
Adulteration is a real and documented risk in ground spices, where visual verification is impossible. Approaches include chromatographic profiling, spectroscopic methods with reference libraries, microscopy, and DNA-based identification for species confirmation. If you buy ground material, authenticity verification belongs in your programme.
Sampling: the step that decides everything
A perfect analysis of an unrepresentative sample is worthless. A defensible sampling plan states how many increments are drawn, from where in the lot, how they are combined and reduced, and how the retained portion is sealed and stored.
Agree in the contract who draws the sample, whether an independent surveyor is used, and how a retention sample is held. When a dispute arises months later, the sealed retention sample is the only physical evidence either side has.
Building a sensible testing programme
- Per lot: the physical parameters, plus whichever contractual parameters your product depends on.
- Risk-based, at a defined frequency: pesticide residues, heavy metals, mycotoxins — tied to commodity, origin and supplier history.
- On qualification and periodically thereafter: the full panel, plus authenticity for ground material.
Testing everything on every lot is unaffordable and unnecessary; testing nothing is negligent. The middle course is a written programme justified by risk, which is also what an auditor will want to see.
HS Herbs issues a lot-specific certificate of analysis with each shipment, and the parameter set is agreed with the buyer against their market and application. Related reading: ISO 22000 in herb processing and our B2B sourcing guide. To discuss a specification, contact our export team.