🍎 Bulk density of cereal grain (mass per hectolitre) — the routine method, 1 l density meter

Food chemistry PN-EN ISO 7971-3

Overview

The standard specifies the routine method of determining the bulk density of cereal grain, called the mass per hectolitre, with the use of manual or automatic (mechanical, electrical, electronic) measuring instruments. The mass per hectolitre is the ratio of the mass of the grain to the volume which it occupies after being poured into a container under the conditions laid down by the manufacturer of the instrument, expressed in kilograms per hectolitre of grain as delivered; it differs from the specific density of the kernels. The second edition ISO 7971-3:2019 replaces the edition of 2009, introducing a conversion formula for the Nilema litre instrument for wheat and barley.

The mass per hectolitre is affected by the space between the kernels (depending on their size and shape) and by the density of the kernels themselves; the manner of pouring and the way the grain settles in the container may cause divergences between instruments, and for that reason every instrument has to be checked in accordance with ISO 7971-2 against the international reference instrument. The annexes of the standard describe two manual instruments of 1 l capacity: KERN (a preliminary container of 1350 ± 10 ml, a funnel of 79.0 mm internal diameter, a piston of 450 g, a measuring container of 88.2 mm diameter) and Nilema litre.

In Poland the 1 l grain density meter (a base with a spirit level, a brass measuring container with a ring, a disc, a cutting knife, a filler and a preliminary pouring container of 1350 ± 10 ml) holds a type approval mark of the Central Office of Measures and a verification certificate; for the measurement a verified electronic balance of accuracy class II is required, and the result is read off from reduction tables or from a balance with built-in software.

Method principle

The mass per hectolitre is obtained from the mass of a defined volume of grain determined under controlled conditions of filling and flow. The measurement is carried out on grain cleaned of large impurities (straw, stones, large amounts of chaff), at a temperature equal to the temperature of the room, in two repetitions — preferably on two different portions, because pouring the same portion again reduces the friction between the kernels and raises the result. A manual instrument is set on a hard, horizontal (spirit level) base and filled without jolts according to the manufacturer’s instructions; the grain in the 1 l container is weighed to the nearest 1 g (smaller containers — to 0.1 g). Automatic instruments display the result directly after the application of correcting formulae; they require the selection of the right cereal (calibration), the recommended volume of grain and the emptying of the collecting drawer between samples. The result is the mean of two determinations to 0.1 kg/hl, if the condition of repeatability r = 0.4 kg/hl has been met (for 67.5–84.5 kg/hl); otherwise the mean of four measurements.

Applications

• Assessment of the commercial quality and classification of wheat, barley, oat and rye grain at collection and in trade
• A quality requirement for milling wheat in tenders and strategic reserves
• Estimation of the milling yield and assessment of the plumpness of the kernels in breeding and in field trials
• Routine control in milling laboratories and grain elevators, also in combination with NIR analysers

Key parameters

Standard

Standard number

PN-EN ISO 7971-3:2019-03

Title (PL)

Ziarno zbóż — Oznaczanie gęstości w stanie zsypnym, zwanej masą hektolitra — Część 3: Metoda rutynowa

Title (EN)

Cereals — Determination of bulk density, called mass per hectolitre — Part 3: Routine method

Step-by-step procedure

1. Preparation of the sample

   Remove large impurities (straw, stones, large amounts of loose chaff). Bring the grain to the temperature of the room in which the measurement is carried out.

2. Setting up the manual instrument

   Check the cleanliness and the working order of the parts. Set the instrument on a hard, flat base and level it with a spirit level.

3. Filling

   Pour the grain in accordance with the instructions of the manufacturer of the instrument (for example first to the mark of the 1350 ml container, then through the funnel into the measuring container), avoiding any jolts; if the instrument is jolted, invalidate the measurement and start again.

4. Cutting off and weighing

   Cut off the excess grain with the cutting knife, weigh the grain from the 1 l container to the nearest 1 g (a smaller container — to 0.1 g) and read off the mass per hectolitre from the reduction tables or from the balance with software.

5. Automatic instrument

   Set it on a horizontal surface away from extreme temperatures, moisture, dust and vibrations; select the right cereal (calibration), use the recommended volume of grain, empty the collecting drawer between samples; read the result off the display.

6. Repetition

   Carry out a second determination, as far as possible on another portion of grain from the same sample.

7. Result and test report

   If the difference does not exceed r = 0.4 kg/hl, give the mean of two determinations to 0.1 kg/hl; otherwise carry out two additional measurements and give the mean of four, describing in the test report the conditions under which the result was obtained. The test report: the method with a reference to ISO 7971-3, the result, details not laid down in the standard, the identification of the sample.

Required equipment and apparatus

Health and safety (OHS)

• Grain dust — the measurement in a ventilated room, if necessary a dust mask
• The cutting knife with a hardened V-shaped blade — guide it by the handle, away from the fingers
• The weight of the instrument (about 6 kg) and of the balance — a stable table, avoid jolts also for the sake of the correctness of the measurement

Frequently asked questions