There is no single legal moisture limit for grain in international trade. Moisture is a contract parameter, not a regulatory one, and the numbers that circulate as if they were law are trade practice built on what actually keeps grain safe in store.
The working figures are these. Milling wheat is normally contracted at not more than 14 per cent. Feed barley trades around 14 to 14.5 per cent, while malting barley is usually tighter, at not more than about 13.5 per cent, because germination has to be preserved. Maize is often accepted a little higher at origin and dried down for storage. Oilseeds are far tighter: sunflower and rapeseed are held well below 9 per cent because oil-bearing seed spoils fast.
The reason those levels exist is biological rather than commercial. Grain does not spoil at a moisture percentage; it spoils at a water activity that supports mould growth, and moulds are what produce storage mycotoxins such as ochratoxin A. Above roughly 14 per cent in cereals, the equilibrium relative humidity inside a bulk becomes hospitable, and the risk climbs steeply with temperature. The contract number is a proxy for keeping the bulk below that threshold for the length of the voyage and the storage after it.
Three practical points. First, moisture is traded against an allowance schedule rather than as pass-or-fail, so a marginally wet cargo is usually priced rather than rejected – but know the schedule before you argue. Second, the reference method matters: ISO 712 is the standard for cereals and cereal products, and a portable meter on a truck ramp is an operational indication, not a contract result. Third, the moisture that matters is the moisture at discharge, because moisture migrates within a bulk during a voyage and a container loaded warm and discharged cold will have wet spots even if the average is unchanged.
For the buyer, that last point is the argument for specifying a sampling plan and a discharge analysis rather than accepting a loading certificate as final. See the grain export documentation guide for how the certificates fit together.