Walk into any onion packing house and you'll see onions of all shapes and sizes. Some are round. Some are oval. Some are flat. But here's the thing: not all sorting machines handle every shape equally well. Choosing the wrong one means inconsistent grades and lost revenue.
The Shape Factor That Changes Everything
Onions come in two main shape categories. Yellow and white onions are round or oval. They roll smoothly and predictably between rollers, making them ideal for diameter-based sorting. Purple onions (also known as red onions) are flat and irregular. They don't roll the same way. They shift, tilt, and can get wedged into gaps that donât represent their true size.
This isn't a small detail. For packers processing tons of onions per day, matching the grader to the onion shape is the difference between accurate grades and costly mistakes.
Three Grading Technologies for Three Onion Types
Fstsort offers three onion sorting technologiesâeach designed for a specific onion shape and market need.
Drum Grader â Best for Flat Purple Onions
Flat purple onions have an irregular shape that doesn't roll predictably between rollers. The drum grader uses a rotating drum with round holes that measure diameter from every angle as the onion tumblesâensuring accurate sizing regardless of shape.
Feature | What It Means for Your Operation |
|---|---|
High capacity | Handles large volumes with simple, reliable operation |
Simple structure | Easy to maintain, low operating costs |
Customizable drum holes | Match your exact diameter requirements |
Best suited for: Flat purple/red onions, high-volume packing, simple grading needs.
Roller Grader â Best for Round Yellow & White Onions
Round yellow and white onions roll consistently between rollers. The roller grader uses a series of forward-moving rollers with gradually widening gapsâround onions fall through at the precise point that matches their diameter.
Feature | What It Means for Your Operation |
|---|---|
Gentle handling | Smooth rollers and food-grade materials prevent bruising |
Reduced damage | No crushing, no skin abrasionâonions stay intact |
Adjustable gaps | Fine-tune grade sizes as market requirements change |
Best suited for: Round/oval yellow and white onions, packers who prioritize gentle handling and product quality.
Screen Sizer â Best for High-Precision Round Onions
For packers who need the highest precision, the screen sizer uses customizable screen holes to sort round onions with exceptional accuracy.
Feature | What It Means for Your Operation |
|---|---|
High precision | Customizable screen holes for exact size specifications |
Large capacity | Handles commercial volumes with ease |
Easy maintenance | Screens are simple to replaceâreduces downtime |
Best suited for: Round/oval yellow and white onions requiring precise sizing, export markets with tight specifications.
Quick Comparison: Which One Fits Your Onions?
Onion Type | Recommended Grader | Why |
|---|---|---|
Flat purple onions | Drum Grader | Rotating drum measures diameter from every angleâshape doesnât affect accuracy |
Round/oval yellow & white onions | Roller Grader | Gentle handling, reduces bruising, perfect for standard packing |
Round/oval yellow & white onions (high precision) | Screen Sizer | Customizable screen holes for the highest precision sizing |
Explore the full specifications on our onion sorting grading machine page â
Built for Onion Packers
Onions come in different shapes. The right grader makes sure every onion reaches the right marketâat the right price. Choose the technology that fits your onions, your volume, and your quality standards.
All three graders are built with stainless steel contact surfaces for hygiene and durability, with compact structures and pulley devices for easy movement. Each machine can be customized with additional modulesâloose skin remover, automatic box filling, or bagging systemsâto build a complete packing line.
Fstsort has already delivered onion grading solutions to packers across multiple markets, including Senegal, Turkey, and the United States.