Optical Sorting versus Precision Density Sorting

- Christian Burney

Optical color sorting is regarded by some in the seed industry as an exciting, newish technology that offers innumerable advantages over other forms of product separation. While it is true that modern optical color sorting technology is powerful, we fear that seedsmen risk losing quality product by relying solely on optical color sorting systems over additional processes.

Optical color sorters first entered the commercial market way back in the 30s, and naturally, their potential has surged since then. Optical color sorting is largely visually based. Optical sorters today utilize shape recognition and monochromatic, dichromatic or RGB (full color) camera technology to accept or reject seed based on color, length and surface integrity of a given product. In some instances, this sorting method can capture bad seeds that would skirt around other forms of sorting and separation. For example, some diseases will render a seed discolored or scarred, but won’t affect the weight or mass of the seed itself.

But in many circumstances, the opposite is true, too. Many diseases will cause a seed to rot from the inside out, affecting the mass and weight of a seed without causing visual damage or discoloration to the seed’s exterior. In addition, if the interior of a seed is not fully developed, the germination and vibrancy of the seed may be inferior. The best way to remove these bad seeds from a production line is, no contest, through density separation.

I’m not here to advocate for density separation over optical sorting, or vice-versa. More so, I want everyone to be aware that the two methods work best in tandem. Each method is a test of very specific, defined variables – if one were to plot a Venn diagram with Optical Color Sorting on the left and Precision Density Separation on the right, there would be little overlap in the metrics they operate by. But, those metrics exist in all sorts of seeds, and using just one sorting method while ignoring another will guarantee that quality control is ultimately flawed.

In my experience, some seed facilities will determine that a seed’s quality is acceptable based strictly on what it looks like to their own two eyes. They will loosely examine the seed as it travels across a conveyor and make the call to reroute the seeds passing by the gravity separators.

Talk about optical sorting. I can’t dissuade one from doing this enough. As I mentioned earlier, visual discrepancies in seeds aren’t the only variables to consider; weight and mass are something for which optical sorters, and human eyes, just can’t account for. What is your standard for quality using optical color sorters and precision density separators?

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