A green tea certificate of analysis (COA) can provide credible evidence of the results obtained for the identified sample, using the listed methods, on the reported dates. It cannot by itself prove that the sample represented the entire shipment, that every relevant hazard was tested, that the tea meets every destination law, or that the delivered bags are the same lot. Buyers should approve a COA only after connecting four things: the contract requirement, the lot and sampling record, the laboratory's competence for the specific work, and a stated acceptance rule.

First identify what document you received

"COA" is a trade label, not a guarantee of one universal format. One supplier may issue a one-page summary copied from production records; another may forward a multi-page third-party laboratory report. Either can be useful, but they carry different evidence. Check who issued the document, who performed each test and whether the COA reproduces, summarizes or attaches the underlying report.

ISO states that ISO/IEC 17025:2017 is the international standard for testing and calibration laboratories and that it addresses competence, impartiality and consistent operation. The current edition was confirmed in 2023. Accreditation against that standard increases confidence in work within the accredited scope; it does not certify the tea, the supplier's management system or every activity the laboratory offers.

Keep five requirement types separate

  • Trade reference: a grade or style such as Chunmee 41022. It does not define a test panel.
  • Legal requirement: a mandatory destination rule. The importer must identify the jurisdiction, commodity and effective version.
  • Voluntary standard: a technical standard such as an ISO sampling or test method. It becomes binding only when law or contract incorporates it.
  • Buyer specification: the buyer's agreed limits, methods and reporting needs, which may be tighter or broader than law.
  • Contract requirement: the obligation accepted by buyer and seller, including which document controls and what happens after a nonconforming result.

A COA is evidence used against those requirements; it is not a replacement for defining them. Use the site's bulk green tea specification template to fix the question before asking a laboratory to answer it.

What a well-controlled COA can support

When the sample identity, method and reporting chain are clear, a COA can show the measured result for stated parameters such as moisture, ash, water extract, a defined pesticide panel or another agreed item. It can identify the reporting unit, detection or quantification limit, test date and the laboratory responsible. If the laboratory provides a statement of conformity, it can also show which specified requirement was assessed and which decision rule was applied.

That is valuable evidence for a shipment-release file. It lets the buyer compare results with the signed specification, detect missing tests, track trends between lots and decide whether a result needs clarification, retesting or contractual action. It is strongest when accompanied by the sampling report, chain of custody, retained split sample and laboratory accreditation scope.

What the COA cannot prove on its own

  • Representativeness: a valid result describes the material tested. Without a controlled sampling record, it does not show how well that portion represents hundreds of bags.
  • Untested hazards: a pesticide screen covering 300 named analytes says nothing about excluded substances, contaminants or microbiological items.
  • Legal compliance: a list of numbers does not establish that the correct market, commodity, residue definition, effective limit and transition rule were used. Our EU pesticide MRL guide shows why the legal snapshot must be preserved separately.
  • Shipment identity: the report does not prove that the loaded tea is the sampled lot unless lot marks, seals, packing records and loading controls connect them.
  • All sensory quality: laboratory data cannot fully establish leaf appearance, aroma, liquor, taste or match to an approved reference sample. Use a repeatable green tea sample evaluation alongside analytical review.
  • Future stability: results do not guarantee the condition after poor storage, moisture exposure, odour contamination or package damage.
  • Authenticity: a logo, stamp or PDF alone does not prove that the issuing laboratory created the document. Verify report numbers or signed originals when risk warrants.

Use this 12-point COA review checklist

CheckpointWhat to verifyEvidence to keepStop if
1. IssuerLegal laboratory or supplier name and contactOriginal report or controlled COAIssuer is unclear
2. Report controlUnique number, version, issue date, pages and authorizationComplete signed PDFPages or amendments are missing
3. ProductGreen tea type, form and relevant gradeSpecification referenceDescription is only "tea"
4. Lot linkSupplier lot, package count, weight and production or packing referenceLot and packing recordsCode does not match shipment
5. SampleWho sampled, where, when and howSampling report and sealsSource is unknown
6. Receipt conditionLaboratory sample ID, receipt date, seal and conditionChain of custodyIdentity or seal differs
7. Test scopeExact parameters, analytes and exclusionsControlled test listPanel name hides exclusions
8. MethodMethod identifier, edition and tea-matrix suitabilityQuotation and reportMethod is absent or unsuitable
9. ResultValue, unit, basis, LOQ/LOD and flagsUnrounded laboratory resultUnit or basis is ambiguous
10. AccreditationBody, certificate status and scope for matrix/methodAccreditor directory and scopeLogo is the only evidence
11. RequirementNamed law, standard or buyer limit and versionControlled specificationLimit source is not stated
12. DecisionResults covered, conformity statement, uncertainty and decision ruleRelease record"Pass" cannot be reconstructed

Verify accreditation at the activity level

Do not stop at "ISO 17025 laboratory." ILAC explains that accredited laboratories perform activities defined in their scopes and that accreditation bodies maintain directories of accredited laboratories. The current ILAC G18:01/2024 guidance says describing and assessing the scope is central to showing competence for the services listed.

Open the accreditation body's directory and match the legal laboratory name, location, certificate number, current status, matrix or material, test activity and method. A pesticide method may be accredited for one food group but not dried tea; a laboratory may also issue both accredited and non-accredited results on one report. Ask it to mark the status of each relevant line. International recognition can improve acceptance, but ILAC cautions that it does not guarantee every regulator or market participant will accept a report; destination-specific rules still control.

Treat "pass" as a decision, not a decoration

A measured value and a conformity statement are different outputs. ILAC G8:09/2019 explains that when a customer requests pass/fail, the specification and decision rule should be defined, communicated and agreed. A conformity statement should identify the results to which it applies, the requirement met or not met and the rule used. This matters near a limit because measurement uncertainty creates a risk of false acceptance or false rejection.

Before testing, state whether the laboratory should report numbers only or also decide conformity. If it will decide, agree the specification limit, rounding, uncertainty treatment, any guard band and the action for an inconclusive or failed result. Do not add your own silent uncertainty allowance after the report arrives.

Connect the certificate to a representative lot sample

ISO 1839:1980, which ISO currently lists as published and confirmed, applies to sampling tea containers of all sizes and covers sample packaging, labelling, dispatch and the sampling report. A contract may adopt it as a voluntary reference, but the sampling instruction still needs the lot definition, package selection, increments, composite, division into laboratory and referee portions, seals and authorized sampler.

The practical evidence chain is: signed specification → defined lot → documented sampling → sealed laboratory portion → authenticated report → decision record → unchanged lot loaded under matching marks. If one arrow is missing, classify the COA as limited evidence and resolve the gap before release. Yunjing Tea's quality-control checkpoints provide the wider sample-to-shipment context.

Common buyer mistakes

  • Accepting a supplier's one-page summary without the underlying laboratory report.
  • Checking the accreditation certificate but not the current technical scope.
  • Treating "not detected" as zero without reviewing the method and reporting limit.
  • Comparing results expressed on different bases or in different units.
  • Assuming a broad panel includes every destination requirement.
  • Letting the tested lot be blended, repacked or substituted without new controls.
  • Accepting a "pass" when the limit, result coverage and decision rule are absent.

A practical release decision

Mark every checklist line verified, clarify or stop. Release only when the critical identity, sample, scope, method, result and decision links are verified. Clarify administrative gaps that do not change identity or validity; stop when the wrong lot, incomplete scope, unsuitable reporting limit, unverifiable report or undefined conformity rule could change the purchasing decision. Keep the COA with its specification, sampling report, accreditation scope, chain of custody and final release approval.

For a product-specific review, send Yunjing Tea the destination, tea type, lot size, required test list and COA format before sampling or ordering.

Sources checked 3 August 2026: ISO/IEC 17025:2017, testing and calibration laboratory competence; ILAC guidance series, including G8:09/2019 and G18:01/2024; ILAC accreditation and international-acceptance FAQs; and ISO 1839:1980, Tea — Sampling.