How do laboratories determine the quality of wheat? - articles from the OLIS press center

How do laboratories determine the quality of wheat?

Grain quality is the most important indicator that affects production costs. Each grain elevator is equipped with a special laboratory where it is tested. Grain is subjected to comprehensive testing, after which its quality and purpose are determined. Grain cleaning equipment must be used. It helps to remove various debris and impurities that reduce its value.

How is sampling carried out?

First of all, samples are taken to be tested. The material is selected on sight and tested by a laboratory technician in strict compliance with GOST regulations. The number and volume of samples taken depends on the carrying capacity of the supplier’s truck. Many elevators take the first sample in automatic mode, although the regulations recommend that it be taken through a manual sampler.

“Each method has its advantages. For example, the manual one is time-tested and regulated by technical rules. But the use of automation increases the accuracy of tests, eliminating the human factor. Our organisation actively uses both methods,” says Yulia Sagaidak, laboratory technician at SME Nika-Tera.

The taken sample is transferred directly to the laboratory, where the average sample is extracted in automatic mode (according to the standards, its weight should be from 2 kg).

The next stage is organoleptic analysis. It determines the colour of the grain sample and its smell. It is necessary that the grain aroma fully complies with the established standards.

The next step is to measure the degree of contamination of the grain with pathogens. For this purpose, the middle sample is sieved through special sieves with a diameter of 1.50 and 2.50 mm. If traces of pests are found, the degree of damage is determined. The number of parasites per 1 kg of grain is used to calculate the index.

How is nature calculated?

This indicator corresponds to the mass of 1 litre of raw material and is displayed in grams (1 g/l). A specialised purge is used for the work.
“First, a large suspension is sifted out of the sample using a 6.00 mm sieve. The sample is weighed and, according to certain calculations, mixed into the total mass. The sample, which is free of debris, is used to determine the natural content. This parameter is detected along two parallels, after which the average value is displayed.

If the test result falls within the established limits, the delivery is accepted and the grain is considered suitable, otherwise the batch is rejected and returned,” explains Natalia Bukh, technical laboratory assistant. The analyser, which uses a rapid method, detects the mass fraction of protein compounds and moisture levels.

Once the grain is deemed suitable, it is subjected to the following analyses:

  • level of moisture resistance;
  • gluten parameters;
  • drop number;
  • volume of impurity;
  • indicator of vitreous;
  • degree of damage to raw materials (diseases and pests);
  • Calibrate the main grains.

The trash (grain) impurity is determined by sieving the sample on different sieves. Large crystals are classified as minerals. The result directly affects the grain category, which is determined after laboratory testing.

During the disassembly of the canopy, the presence of additional inclusions (organic matter, spoiled material, etc.), grain impurities (germinated, empty, broken) is determined. The next stage of the test reveals the mass of grains spoiled by the turtle bug.

“Grains damaged by the bug pest are not classified in the DSTU, but their presence affects such an important parameter as gluten quality,” explains Irina Korol, quality manager.

How is humidity determined?

To find out this parameter, a grain sample is ground using a special mill. Before the test, the device is completely cleaned and sanitised to ensure the most accurate result. It is better to use modern systems. For example, milling used to be carried out at LMZ mills. The grain was heated in the process, which reduced the quality and accuracy of the final result.

According to leading experts, the best products in the mill category are Swiss-made products that control the process and prevent the temperature of the sample from rising. The ground meal is sent to a special container, which is immediately sealed to prevent moisture evaporation.

Every 10 days, the grinding size is monitored. For this purpose, the meal is additionally sieved through a sieve with a diameter of 0.80 and 1.00. Permissible residue values are a maximum of 5% to 1.00% and 50% to 0.80%.

The milled grain is fed into all-metal boxes, where the weight of the weights is brought to 5 g. The containers are sent to a specialised drying cabinet, where they are kept for 35-40 minutes at +130°C. After that, the contents are weighed.

“The average is determined using Infratec express analysers and an Aquamatic moisture meter. All the equipment is calibrated before work. We use a standard methodology to determine the moisture content,” explains the laboratory technician.

How to determine the drop rate?

To determine this parameter, 300 g of a sample is taken from the middle sample. It is cleaned of impurities (debris and grain), then grinded through a sieve with a diameter of 0.80 mm. For this purpose, we use a mill from PERTEN. This equipment allows us to carry out high-quality grinding of the taken raw materials and send them to hermetic chambers.

Then, according to GOST standards, the moisture content is determined. Two canopies are separated from the sample. Their weight is determined according to the table (parameters are set at 6.40-7.30 g).

The resulting suspensions are placed in volumetric test tubes and filled with distillate in a volume of 25 cm3. The tubes are tightly closed and shaken vigorously. The stirring rod mixes all the particles into a single substance. After mixing, the tubes are placed in a container where they are kept in a water bath.

During the process, the contents of the tubes are subjected to intensive automatic stirring (the stirrers start rotating 5 hours after the procedure begins). After a minute, they stop working, freezing in the upper position. Free fall is performed in the volume determined by a special counter.

“The falling number is equal to the reading in seconds. The faster the process, the lower the quality. In the course of the analysis, we determine the class of the material according to GOST standards. This measure allows us to determine the mobility of a specialised enzyme involved in the breakdown of starch and glycogen,” says Iryna Korol.

We use this parameter to determine baking performance. The optimal falling number for wheat flour is 235±15 s. In case of a lower result (up to 150 s), it can be assumed that the starch gradually deteriorates, and the dough itself begins to spread, which will have a bad effect on the quality of the bread.

When the falling time is set between 150 and 180 seconds, the dough is too viscous. The bread is baked with a dark colour and an ugly crust. The best indicator is 230-330 seconds, which results in a fluffy and rich pastry. If the falling number is too high, the bread will become dry, pale and start to stale quickly.

How to identify gluten?

To do this, we take a canopy of 25 g so that the final weight of raw gluten is 4 g or more. We take the sample from the meal and pour 14 ml of distillate over it and knead it in a dough mixer. The finished sample is formed into a ball and placed in a special mortar, where it is kept for 20 minutes. After that, the gluten is washed.

At a temperature of +18⁰C, the hull is washed out with the release of starchy substances. This procedure is carried out automatically until the gluten is completely cleaned. The mass is squeezed by hand and weighed. The deformation index (DI) apparatus is used to determine its elasticity. This data is used to determine the baking properties of the wheat.

“If this parameter is too low, the bread will not rise well and the crust will crack. If the level is increased, the body will start to spread. For this reason, enterprises use grains of different quality to obtain high-quality raw materials for the batch to be baked. It is also necessary to use special equipment to produce flour, which allows us to get really high-quality material,” says Iryna Korol.

“Drunken bread”: what is it?

Grain samples are selected and further tested for parasitic and fungal pathogens. Samples infected with a fungus (fusarium) are detected. Products made from such flour are hazardous to human health and are not suitable for human consumption.
Bread baked with fusarium flour is called “drunken” bread. When it is consumed, poisoning occurs, the symptoms of which resemble those of alcohol consumption. The victim feels nauseous, weak, and vomits violently. Gradually, the symptoms disappear on their own and do not cause significant harm to health.

On average, it takes us about 1.5-2 hours to carry out the analysis. However, in the middle of the harvest, when the company has a heavy workload, the time for research and sampling of wheat is reduced.