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FOOD


only accept a certain degree of granulation. ‘If a mill doesn’t know the quality of its product it is lost,’ said Hahne. A rejected batch could be a loss of $10,000 in raw material, just because the mill didn’t meet the quality requirements. In terms of grits, which are particles of


endosperm used in snacks and breakfast cereals, a mill might have an output of 100 tonnes a day of flaking grits – the larger particles – and 500 tonnes a day of snack grits, a finer material sent to snacking companies. Snack grits, as well as being much finer than flaking grits, also might need different fat and moisture content. By using optical techniques during the


process of converting grain to grits, Bühler’s systems can optimise the yield of maize grits by 0.3 per cent. Tis, according to Hahne, can lead to additional earnings for the mill of $200,000 a year. ‘Tis is where we can really convince our customers why they need our technologies,’ Hahne said. In addition, since Bühler’s sensors work online during the process, the mill can save an extra $25,000 a year because it doesn’t have to run as many offline quality control tests on the product. Bühler’s online Particle Size Measurement


Unit is able to measure granulation optically. It uses a camera with a strobed LED to measure the shape and size of coarse


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particles, together with laser diffraction to detect fine particles. Te output of these two sensors gives a particle size distribution between 10µm and 5,000µm. Tis range covers most products in grain processing, Hahne said. Te company’s NIR Multi Online Analyser monitors the fat content of grits using near infrared spectroscopy. Turning to wheat, installing a Bühler


optical sorting platform can give around 0.8 per cent improvement in yield compared to using mechanical cleaning. When that is applied to 80,000 tonnes per year, it adds up to €125,000 of added saving for the customer. ‘A single grain of wheat has very little


value, but when you’re talking about millions of tonnes, even the smallest improvement has an enormous knock-on effect,’ said Dr Tim Kelf, head of sensor development at Bühler. ‘When we’re talking about the 1 to 2 per cent improvement level that we can squeeze out through these optical techniques, that’s enormous for our customers.’


All in the delivery A normal Bühler line will process 10, 20 or even 100 tonnes per hour, and that could be running 24 hours a day. ‘We’re talking about millions of objects per second, and all of them have to go through the imaging area,’


‘We’re talking about millions of objects per second, and all of them have to go through the imaging area’


said Kelf. Ideally, all these particles need to be separated to make life easier from an imaging perspective, although the algorithms are able to extract information from the images even if particles are touching. ‘In order to present grains to an optical


sensor it’s important to understand the physics of it all,’ said Kelf. ‘You need to make sure grains aren’t bouncing, while at the same time the flow of grain needs to be accelerated to 4m/s because otherwise you don’t get the capacity.’ Some products like chickpeas will bounce,


whereas almonds will bounce less. Some grains roll a lot, some products are sticky. ‘It’s understanding the properties of the grain and the material properties of the chute, along with the chute’s geometry, to create a stable feed,’ Kelf said. ‘Tere’s no one solution. For frozen foods you’d use a very different system than you would for rice or nuts.’


g JUNE/JULY 2020 IMAGING AND MACHINE VISION EUROPE 25


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