An assessment of practical methods for collecting samples from lorry-loads of grain

Abstract

The collection and examination of samples is a fundamental component in determining quality of bulk grain. Currently, there is only one, well documented approach to sampling grain: British Standard 5410, which is identical to International Standard 950. However, there is no scientific basis for these Standards.

Grain is an extremely variable commodity so that there is a high probability of quality assessments being influenced by sampling errors. These potential errors are likely to have maximum commercial impact when lorry-loads of grain are sampled at time of sale. Therefore, the influence of sampling methods, sample position and methods of loading lorries, were investigated.

Loads of English feed wheat, all taken from the same batch, were sampled manually with a compartmented spear, automatically with a SAMPLEX C90 vacuum probe and manually at the tailgate during tipping. The lorries were loaded either from an overhead bin or with a front loader bucket. Samples were collected from 8 points with the manual spear or 5 points with the automatic probe, and assessed for moisture content, fine material and hectolitre weight. Assessments were made on individual samples and on a composite made by mixing individual samples. Only a single tailgate sample was collected but this was made up of four scoops taken at intervals as the grain tipped.

In general, there was little difference in the results for hectolitre weight and moisture content produced by the three methods of collecting samples. Manual sampling gave average values that were 0.5 kg/Hltr higher than the automatic sampler, and tailgate samples were 1.6 kg/Hltr higher. There was no significant difference for moisture content. However, with fine material, the differences were more pronounced and tailgate samples gave values 3 - 5% higher than the automatic sampler, which in turn was about 1.4% higher than the manual sampler. The method of loading appeared to have little influence on the results. There was very little correlation between sampling position and any of the parameters measured.

This work demonstrated the inadvisability of basing quality assessments on a single sample. The difference in the numbers of individual samples collected with the automatic probe and manual spear did not exert a large influence on the mean value obtained or on the size of the standard deviation around the mean.

Survey work on grain sampling methods is reported as Project Report No 118.