What is Paddy-to-Brown Rice Conversion Rate?
The paddy-to-brown rice conversion rate (also called brown rice rate) is the percentage of brown rice mass obtained after hulling clean paddy, relative to the sample mass. It is an important indicator for evaluating rice processing quality and is one of the mandatory inspection items in grain purchase, storage, and processing.
The conversion rate is closely related to rice variety, maturity, moisture content, and huller processing effectiveness. Generally, a conversion rate between 75%-82% is considered normal.
National Standard Testing Method (GB/T 5495)
According to the national standard "Inspection of Grain and Oils - Paddy-to-Brown Rice Conversion Rate" (GB/T 5495), the testing method is as follows:
1. Instruments and Tools
- Laboratory Rice Huller: Standard-compliant small huller with roll specifications typically Φ50-80mm
- Analytical Balance: Sensitivity 0.01g
- Grain Sieve: For cleaning impurities and separating paddy from brown rice
- Tweezers, petri dishes, and other auxiliary tools
2. Sample Preparation
1. Sampling
- Extract approximately 150g of clean paddy sample from submitted samples
- Use GB/T 5491 methods for sample division to ensure representativeness
2. Cleaning and Impurity Removal
- Remove impurities and inorganic matter using sieves
- Pick out foreign grains and obviously damaged grains
- Cleaned sample mass should be no less than 120g
3. Moisture Determination
- Determine sample moisture content per GB 5009.3
- Record moisture value for result calculation
3. Testing Steps
Step 1: Hulling
- Place cleaned sample (approximately 100g, precise to 0.01g) into laboratory huller
- Adjust roll gap to appropriate position (typically 0.5-0.8mm)
- Start huller and complete dehusking in a single pass
- Collect all discharged material (brown rice, husks, unhulled grains)
Step 2: Paddy-Brown Rice Separation
- Separate hulling mixture by air separation or manual sorting
- Separate brown rice, unhulled paddy, and husks
- Carefully pick out residual unhulled grains from brown rice with tweezers
Step 3: Weighing
- Weigh obtained brown rice mass (m₁), precise to 0.01g
- Weigh unhulled paddy mass (m₂), precise to 0.01g
- Weigh husk mass (m₃), precise to 0.01g
Step 4: Calculation
Calculate conversion rate using the following formula:
Conversion Rate(%) = (m₁ / m₀) × 100
Where:
- m₀ = Total sample mass (g)
- m₁ = Brown rice mass (g)
Duplicate Test Allowable Difference: The difference between two test results should not exceed 0.5%; otherwise, re-testing is required.
Rice Huller Operating Standards
To ensure accuracy and repeatability of conversion rate test results, laboratory huller operation must be standardized:
Pre-Startup Checks
Equipment Status Check
- Check roll surfaces for cleanliness and damage
- Check roll gap是否符合要求 (measure with feeler gauge)
- Check drive belt tension
- Check feed hopper and air passages for blockages
No-Load Test Run
- Connect power and run no-load for 1-2 minutes
- Listen for normal operation sounds
- Check motor rotation direction
- Confirm no abnormalities before load operation
Operating Points
Uniform Feeding
- Pour sample evenly into feed hopper
- Avoid pouring too much at once causing blockage
- Maintain certain material layer height in hopper
Parameter Adjustment
- Adjust roll gap according to rice variety
- Japonica rice gap can be slightly larger (0.6-0.8mm)
- Indica rice gap can be slightly smaller (0.5-0.7mm)
Single-Pass Principle
- Standard testing requires single-pass hulling
- Do not return discharged material for re-hulling
- Ensure results reflect true conversion rate
Shutdown and Cleaning
- Wait for all material in hopper to enter equipment before shutdown
- Clean residual bran powder and grains from equipment interior
- Clean roll surfaces with brush
- Record usage (date, sample number, roll condition, etc.)
Factors Affecting Conversion Rate Test Results
1. Paddy Factors
| Factor | Effect on Conversion Rate | |--------|---------------------------| | Variety | Japonica typically higher than Indica | | Maturity | Fully mature paddy has higher rate | | Moisture | 13%-15% moisture optimal for testing | | Impurity Rate | More impurities lower results | | Storage Time | Old crop slightly higher than new crop |
2. Operating Factors
| Factor | Effect | |--------|--------| | Roll Gap | Too large: incomplete hulling; Too small: more broken rice | | Feed Rate | Too fast affects hulling effectiveness | | Roll Condition | Worn rolls reduce hulling rate | | Separation Effect | Incomplete air separation affects brown rice weighing |
Common Problems and Solutions
Problem 1: Large Difference Between Duplicate Tests
- Cause: Non-uniform samples, unstable operation
- Solution: Re-divide samples, standardize operation procedures
Problem 2: Low Hulling Rate
- Cause: Excessive gap or worn rolls
- Solution: Reduce gap or replace rolls
Problem 3: Excessive Broken Rice
- Cause: Gap too small or paddy moisture too low
- Solution: Slightly increase gap, adjust paddy moisture
Conversion Rate and Huller Selection
Conversion rate data is not only a quality indicator but also an important reference for huller selection:
- For high conversion rate varieties (>80%), choose hullers with slightly lower hulling rates to reduce broken rice
- For low conversion rate varieties (<76%), choose high-efficiency hullers
- For grain depot purchases, conversion rate is an important basis for grading and pricing
Zhejiang Lianggong Laboratory Rice Huller
Zhejiang Lianggong Machinery produces laboratory rice hullers compliant with GB/T 5495:
- Precision Manufacturing: Roll gap adjustment precision reaches 0.05mm
- Easy Operation: Humanized adjustment handles and feeding devices
- Accurate Results: Verified by multiple inspection agencies with good repeatability
- Durable and Reliable: Core components use quality materials for long service life
For detailed information about laboratory rice hullers, please call 0575-87335525.
