Why Your Sortex Is Rejecting Good Rice — And How to Fix It

By Bajrang Khaitan · Published 26 October 2026

The problem as you see it

You open the reject outlet of the sortex and find more good rice than you expect. Whole, white, well-polished grains are going out with the discoloured ones. The operator says the machine is working, and in a sense it is. But every good grain in the reject bin is rice you have already paid for, dehusked and polished, now heading to the cheaper stream.

The opposite also happens. The reject looks clean, but the buyer finds yellow, chalky or black-tipped grains in the final rice. Both problems usually come from the same few causes.

Why it happens

A colour sorter looks at each grain with cameras as it falls down the chute. When a grain looks different from the setting, a jet of compressed air from an ejector blows it into the reject. Everything depends on three things: the grain must pass the camera in a single, even layer; the camera must see it clearly; and the ejector must fire at exactly the right moment with the right force.

• Uneven feeding. If the vibrator feeds too much rice or feeds unevenly, grains overlap or bunch up on the chute. When the ejector fires at one bad grain, it blows the good grains next to it as well.
• Dirty cameras and glass. Bran dust and fine powder settle on the viewing glass and the lights. The camera then sees grains as darker than they are and rejects good rice. This builds up slowly over a shift, so the rejection rises without anyone noticing.
• Wrong sensitivity settings. Settings that are too tight treat small, harmless colour variation as a defect. Settings copied from another variety, or left unchanged after a change of paddy, give poor results.
• Air supply problems. Low or fluctuating air pressure makes ejectors weak or slow. Water or oil in the compressed air can make ejector valves sticky. Pressure set too high blows neighbouring grains along with the defect.
• Problems from upstream. If the rice reaching the sortex still has bran on its surface, has too many brokens, or carries dust from poor aspiration, the sorter is being asked to fix problems created earlier in the line.

What to check, step by step

1. Study the reject sample. Spread a handful of the reject on a dark tray and count roughly how many grains are good. This tells you whether the problem is feeding, settings or ejection.
2. Feed rate and chute flow. Watch the chute. The rice should flow as a thin, even curtain across the full width. Reduce the feed rate and see whether the good-grain rejection drops.
3. Clean the optics. Clean the viewing glass, camera windows and lights as per the manufacturer's procedure, at fixed intervals in every shift, not only when the rejection is visibly high.
4. Air quality and pressure. Check that pressure at the sorter is stable. Drain water from the receiver and filters, and service the air dryer. Ask whether your compressor is sized for the sorter and all other air users.
5. Program for the variety. Use a separate saved program for each variety or quality you run. When you change paddy, change the program, then check the reject again.
6. Sensitivity, one step at a time. Change sensitivity in small steps and check both the accept and reject samples after each change. Large jumps make it impossible to know what helped.
7. Ejector condition. Run the ejector test if the machine has one. A few failed or sticking ejectors on one channel can send defects into the good rice.
8. Re-sort settings. If the machine has a second-pass or re-sort stage, check its settings separately. A well-set re-sort recovers good grain from the first reject.
9. Upstream quality. Check polish, aspiration and broken content before the sortex. Better bran removal and dust control often improve sorting more than any change to the sorter itself.
10. Keep a log. Note settings, feed rate, air pressure and cleaning times for each shift. When rejection rises, the log shows what changed.

Settings are only half the job

Many mills treat the sortex as a machine that is set once by the supplier's engineer and then left alone. In practice it needs the same daily attention as the whitener or the husker. The operator should know how to read a reject sample, when to clean, and which program to load for each variety. Training one or two people properly on these basics usually does more for recovery than calling the engineer every time something looks wrong.

When to call a consultant

If you have worked through this list and the rejection of good rice is still high, the cause is often a combination of machine settings and process upstream. That needs someone to watch the line running. I can look at the sortex together with the hulling, whitening and polishing sections during a mill visit. If you want the sortex and the rest of the line checked at regular intervals, my annual maintenance support covers that kind of review through the year.