Seeds and spices are cleaned by a sequence of machines, and each one removes impurities by a single property: size, weight, shape, colour or magnetism. A typical line runs from a pre-cleaner to an air-screen cleaner, destoner, gravity separator, length or shape grader, colour sorter and magnet.
Gujarat makers build all of these. The Unjha seed spice trade in cumin, fennel and coriander has kept them busy for decades.
Machines in a typical line
- A pre-cleaner or scalper removes large trash such as sticks, stones and lumps, and protects the machines after it.
- An air-screen cleaner uses vibrating sieves to remove oversize and undersize material, and an air stream to lift off dust and light chaff.
- A destoner uses an inclined vibrating deck and air to separate heavy stones and mud balls of the same size as the seed.
- A gravity separator sorts by density, removing shrivelled, hollow or insect-damaged seed.
- An indented cylinder grader or spiral separator sorts by length or shape, removing broken seed and foreign seeds.
- A colour sorter rejects discoloured seed and foreign matter, as explained in colour sorters.
- Magnets catch iron fragments, and many lines add a metal detector before packing.
Why the sequence matters
Each machine works best when the earlier ones have removed what it cannot handle. A gravity separator struggles if dust and stones are still present. A colour sorter loses accuracy if it receives a heavy load of broken seed.
Capacity also depends on the crop and how dirty it arrives. A cleaner rated for wheat will not give the same output on light seeds such as fennel or coriander. Ask makers for capacity on your crop, at the purity you need.
Your purity target usually comes from your buyer's contract. Some buyers refer to industry cleanliness specifications, such as those of the American Spice Trade Association, while others set their own limits. Confirm results with a lab test, as explained in reading a lab certificate.
Dust, aspiration and hygiene
Cleaning lines produce a lot of dust. A good design includes aspiration hoods, cyclones and a filter so the building stays clean. Closed elevators and conveyors reduce spillage and contamination between lots.
Look for machines that open easily for cleaning between crops. Residue from one spice in the corners of a sieve box can end up in the next lot.
Sieve cloths and screens wear and tear, and a torn screen lets oversize through without warning. Keep spare screens for each size you run, and check them at every crop change. Ask the maker which screen sizes come with the machine, because buyers often need several sets for different crops and grades.
Next step
We find makers with working lines on your crop, arrange trials with your raw material and check purity results before you buy. If you also need grinding, see spice grinding plants. To start, book a free sourcing review.