AQL Sampling Explained for Food Buyers
Acceptance quality limit (AQL) sampling is the standard method for inspecting packed goods by attributes. It is widely used for processed food in cartons, and widely misunderstood.
How it works
ISO 2859-1 links the lot size and an inspection level to a sample size code letter, and the code letter and chosen AQL to a sample size with acceptance and rejection numbers. If the number of defective units found is at or below the acceptance number, the lot is accepted; at or above the rejection number, it is rejected.
General inspection level II is the usual default. Special levels with smaller samples are used for destructive or expensive tests.
Classifying defects
Most food buyers set three classes. Critical defects are those that create a safety risk or a legal problem, such as foreign bodies, a missing allergen declaration or a damaged seal. Major defects make the product unfit for its intended use or likely to be rejected by consumers. Minor defects reduce quality but do not affect use.
Critical defects are often given zero tolerance: any single finding rejects the lot regardless of the AQL table.
Typical choices
- Critical: zero tolerance, or the lowest AQL the buyer accepts
- Major: commonly 1.5 or 2.5
- Minor: commonly 4.0
- Always agree defect definitions in writing, with photographs where possible
Where AQL is the wrong tool
AQL sampling is designed for discrete units such as cartons, jars and packs. It is not suitable for contaminants that are unevenly distributed through bulk product, such as aflatoxins in nuts. Those require the incremental and aggregate sampling methods set out in specific regulations or trade rules. Fresh produce is usually inspected using the OECD and EU conformity check approach rather than ISO 2859-1.