Stones in rice are one of the main reasons some consumers still hesitate to buy locally milled rice. A single small stone can crack a tooth and ruin a brand's reputation. Good rice destoner and paddy cleaning equipment removes stones, sand, straw and dust so that rice mills in Kebbi, Kano, Niger, Ebonyi, Benue, Nasarawa and beyond can sell clean rice that competes with imported brands.
This guide explains where cleaning and destoning fit in the milling process, how the machines work, and how to plan cleaning and weighing in a small or medium rice mill.
Why paddy needs cleaning
Paddy often reaches the mill with:
- Stones and pebbles picked up on threshing floors and roadside drying
- Sand and soil
- Straw, chaff and empty grains
- Dust, metal pieces and other foreign matter
These impurities cause real problems:
- Lower quality and price for the finished rice
- Damage to machines: stones wear rubber rolls in huskers and damage whitening machines
- Lower milling yield, because you pay for and process material that is not rice
- Food safety risks for consumers
Where cleaning fits in the rice milling process
A typical small or medium rice mill follows this sequence:
- Reception and weighing of paddy
- Pre-cleaning to remove straw, chaff, dust and large impurities
- Destoning to remove stones of similar size to the grain
- Parboiling and drying (common in Nigeria for parboiled rice)
- Husking to remove the husk
- Paddy separation to return unhusked grains
- Whitening and polishing
- Grading to separate broken grains
- Final destoning or colour sorting (in larger mills)
- Weighing and bagging
Cleaning and destoning are done before parboiling, and many mills add a second destoning step before packing for extra protection.
How paddy cleaners work
A paddy cleaner, or grain cleaner, uses vibrating sieves and air:
- A top sieve catches straw, panicles and large impurities.
- A bottom sieve lets sand and small seeds fall through.
- Air aspiration blows off dust, chaff and light, empty grains.
The grain and seed cleaner machine (around 1 t/h) combines sieves and air aspiration in one unit. It is also useful for cleaning maize, sorghum, soybean and seed grain.
How a rice destoner works
Sieves cannot remove stones that are the same size as rice grains. A destoner separates them by density instead.
The rice destoner machine (1 tonne/hour) uses an inclined, vibrating deck with air blowing up through it. The lighter grain floats on the air cushion and flows down the slope, while heavier stones stay in contact with the deck and are pushed up to a separate outlet.
Rice destoner and paddy cleaning: getting good results
- Clean before you destone. Removing straw and dust first lets the destoner work properly.
- Feed evenly. An uneven feed overloads the deck and lets stones pass.
- Adjust air flow and deck angle. Too much air carries stones with grain; too little lets grain fall into the stone outlet.
- Check the stone outlet. A little grain in the stone outlet is normal; a lot means settings need adjusting.
- Keep screens and decks clean. Blocked holes reduce performance.
- Destone again after parboiling if drying on open floors picks up new stones.
Better still, reduce stones at source. Encourage farmers and aggregators to dry paddy on tarpaulins or concrete floors rather than bare ground or roadsides.
Choosing the right capacity
Match cleaning and destoning capacity to the rest of your mill. If your husker and whitener process about a tonne of paddy per hour, your cleaner and destoner should handle at least that, with some margin, so they never hold back production. Consider:
- How many tonnes of paddy you mill per day, and for how many hours
- Whether you parboil, which adds steps where paddy can pick up dirt
- Whether you clean only paddy, or also grade and destone milled rice before packing
- Power supply: motors and fans must suit your grid or generator
Mills that also buy and resell maize, sorghum or soybean often choose a cleaner that can be adjusted for several grains, so the same machine earns its keep all year.
Weighing paddy and rice
Weighing tells you what you paid for, what you produced and where you lost it.
- Paddy intake: weigh bags on a 5 tonne platform scale or a heavy-duty floor scale. Mills receiving lorries need a weighbridge.
- Moisture: check paddy moisture with a digital grain moisture meter so you do not pay for water.
- Finished rice: weigh every bag before closing so customers receive the full weight printed on the bag.
Comparing paddy intake with finished rice gives your milling yield. Cleaning reduces the amount of rubbish counted as paddy, so your yield figures become more meaningful. Keep scales accurate with regular calibration.
What drives the cost of cleaning and destoning machines?
We do not publish prices in this guide. The main factors are:
- Capacity in tonnes per hour
- Single cleaner, destoner or combined unit
- Motor power and fan size
- Material quality and build
- Delivery to your state and installation
See each product page for current pricing or request a quote.
Clean rice, better prices
Investing in rice destoner and paddy cleaning equipment protects your machines and your brand. Kira Scales has supplied weighing equipment to agro-processing plants across Nigeria, and also supplies grain cleaning and destoning machines alongside scales and weighbridges. We serve all 36 states and the FCT.
Contact us or call or WhatsApp +234 803 435 4829 with your daily paddy volume and location to request a quote.
Frequently Asked Questions
How do I remove stones from rice?
Use a destoner, which separates stones from grain by density using a vibrating deck and air flow. Clean the paddy first and destone again before packing for best results.
What is the difference between a paddy cleaner and a destoner?
A paddy cleaner uses sieves and air to remove straw, sand, dust and chaff. A destoner removes stones the same size as rice grains, which sieves cannot separate.
Can a destoner be used for other grains?
Yes. Destoners and grain cleaners can be adjusted for maize, sorghum, beans and other grains, with settings changed for each.
Why does local rice still have stones after destoning?
Common causes are uneven feeding, wrong air or deck settings, or new stones picked up when parboiled paddy is dried on open ground. Adjusting settings and adding a final destoning step usually solves it.
Where should the destoner go in a rice mill?
Place it after the pre-cleaner and before parboiling or husking. Many mills add a second destoning step before bagging.
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