Expert advice for accurate grain sampling

Last year’s poor wheat quality raised questions on the accuracy of cereal sampling and testing. With harvest approaching, NFU chief arable adviser Guy Gagen outlines how it should happen.


Last year’s experience of some hefty deductions for specific weight following surprise test results prompted members to ask how cereal sampling should happen on farm and at the intake.


Armed with this knowledge, growers can then avoid these unexpected results and limit the resulting claims by resolving any apparent discrepancies early.


But how should growers approach on-farm sampling and what is the sampling and testing approach taken by mills and merchants at intake?


Starting with sampling, work has shown that if it is not done carefully, inaccurate sampling can be the source of up to half of the potential error in grain quality analysis.


As grain is, by its nature, variable, to gain a representative sample, a larger “aggregate” sample should be drawn for each bay, bin or lorry to be assessed, thoroughly mixed and then reduced to a laboratory-sized sample, usually 1kg-3kg, to reduce the chance of sampling error.


On-farm sampling


Representative samples collected on farm and accurately analysed form the basis of any crop marketing campaign, with growers knowing exactly what they have in each heap. It should ideally involve taking samples from trailers or a dryer, which are combined into a representative sample for each 100t in store.


With these results, growers can segregate grain by quality and variety. Then they can match grain batches to buyers’ specific needs, and be more confident in questioning intakes where results do not tie in with expectation based on their own testing.


At intake sampling


Within most grain contracts, intakes should follow the International Standards (ISO) for sampling, which requires them to take eight sub-samples from a 29t lorry to achieve a representative sample for analysis.


Most automatic samplers are designed to allow grain to fall into an opening, then the air-flow takes the grain away. Air-assisted grain transfer in itself does not favour lighter material, but its movement along the pipework can cause considerable separation of screenings. “Vacuum” samplers are very rare and should be used even more carefully.


Once a sample has been taken, it must be carefully and thoroughly mixed and then divided until a sample size suitable for use in a laboratory is achieved.


Laboratory analysis


Sampling is a wasted effort if subsequent analysis (taken on farm or at intake) gives inaccurate results. Testing accuracy depends on equipment, method and operator, and each element must be up to the standard required.


For example, equipment must be fit for purpose, calibrated and ready to use; an accepted and documented method must be used; and the operator must be qualified, competent and trained.


Equipment used for routine analysis should be calibrated against official reference methods, and regular ring testing has been established within the grain trade, feed milling flour milling, malting and other users.


Remember, ring testing and independent analysis are only relevant if the sample was taken and handled properly beforehand. Samples submitted for independent testing should be analysed using reference methods and not by rapid or other methods.


Claims


Within most ex-farm grain contracts, when grain is sold subject to a specification and analysis, the buyer can claim fallbacks to be agreed or to reject the goods on the basis of intake analysis. When the buyer does this, a representative sealed sample shall be drawn and, if requested by the seller, sent to an agreed independent analyst to justify any claim or rejection.


If requested by the seller, this representative sealed sample shall either be jointly or independently drawn where practical. The cost of independent sampling and analysis in this case will be paid by the seller if the claim or rejection is correct. If it was incorrect, the buyer will cover the costs.


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