|Flour is not just flour. Different qualities of flour are distinguished by colour and the number of specks, among other things. The lightness or colour of the flour is influenced by three factors:
- Contamination of the endosperm through bran particles
- The natural pigment content that colours flour/semolina yellow
- The granulation.
Specks can be visible all the way through to the end product, for example as dark spots in pasta. For consumers, these dark spots create a feeling of ‘low quality goods’. Therefore, for certain applications the following rule applies: The ‘whiter’ the flour and the fewer specks it has, the higher its quality.
Colour: An eye and experience
The accurate determination of colour and the exact analysis of the number of specks is of central importance in fine-tuning mills and defining the quality of the flour. For hundreds of years, millers have depended on their eyes and experience for colour and speck control. However, with all due respect for the abilities of the miller, “eye-balling” is a subjective judgment and dependent on soft factors such as the type of lighting and the observer’s current condition. To compensate, millers have also recently been using hand measurement and laboratory devices with which the colour of a flour sample can be determined by its position in the so-called tristimulus colour spectrum (L*a*b*).
Brown specks are small bits of the grain hull while black specks come from impurities which end up in the milling product through suboptimal settings in the cleaning. The volume of brown and black specks contained in the flour allows inferences to be made about errors in various process steps.
Determining the number of specks, however, is painstaking work. One possibility is to count the number of specks on an exactly defined surface. The accuracy of this depends on the judgment and physical condition of the person counting on that day and the lighting. Counting can also be done by laboratory equipment.
Whether the colour analysis and number of specks is determined by visual inspection or using measurement devices – in both cases the results are a snapshot based on sampling. With the new online colour and speck analyser MYHB, Bühler has revolutionised colour and speck control. The system allows continuous monitoring of speck count and product colour in the on-going production of flour and semolina (soft wheat/durum). The core of it is a high-resolution special camera which is directly integrated into the gravity spouting. The camera delivers reproducible colour values in the CIE colour spectrum (L*a*b*) and continuous images of the product as it passes by. The constant analysis enables averaging the colour and speck values for a large measuring surface. Colour deviations from ΔE = 0.2 can be identified. In comparison, the human eye can only identify colour deviations of ΔE = 0.5. The analyser MYHB also recognises brown and black specks starting from a minimum of 80µm and can classify them according to their size.
The MYHB software reports unacceptable deviations according to individually defined alarm thresholds with no time lapse. The images and the speck reports enable the miller to more accurately limit the causes of the colour deviation and specks and to introduce corrective measures.
Combination with NIR
The MYHB system for colour and speck analysis is excellently suited for combination with the NIR multi online analyser MYRG. This system is based on the near infrared (NIR) generation with diode array technology and is used for continuous monitoring of ingredients such as protein, ash, moisture or starch damage in raw, intermediate and end products in the grain processing industry. Both systems can be used for multiple measuring spots in the most varied combinations, and are operated with a common software. The software provides a clearly structured user interface with current measurement values and trend charts. Finally, integrating it with the process management system, WinCos, ensures seamless documentation and traceability.