How Does Paddy Drying Affect Broken Rice Rate and Milling Yield?

How Paddy Drying Affects Rice Milling

The condition of paddy entering the mill is as important as the settings of the milling machines. Two batches of the same variety can produce different results when their moisture history, storage condition and kernel strength are different.

Even with identical mill settings, the second batch may produce more broken rice. This is why a high broken rice rate should be investigated across the entire post-harvest process.

Where Does Broken Rice Come From?

Kernel breakage can occur during handling, husking, paddy separation, whitening, polishing and grading. Kernels already weakened by fissures are more likely to break when mechanical forces are applied.

Drying is an important upstream factor, but variety, harvesting, handling, storage, husker adjustment, whitening pressure and polishing settings also affect the final result.

Why Do Kernels Fissure During Drying?

Moisture moves from the center of the kernel toward its surface. If the outside dries much faster than the inside, a moisture gradient develops.

A fissured kernel may remain intact while it is still paddy, then break along the weakened area during husking, whitening or polishing.

Why Maximum Drying Speed Is Not Always Best

Higher drying intensity can shorten process time, but moisture inside each kernel needs time to migrate and redistribute. When surface moisture leaves too quickly, the difference between the outer and inner parts becomes larger.

Drying temperature should be selected according to paddy variety, initial moisture, target moisture, dryer design, airflow, residence time, grain circulation, drying stages and final use.

Average Moisture vs Moisture Uniformity

Average moisture alone does not describe the complete condition of a paddy batch.

The goal is therefore appropriate and uniform moisture, rather than the lowest possible average reading.

Problems Caused by Over-Drying or Under-Drying

Neither extreme is desirable. The target should match the intended storage period, climate, silo management, milling schedule and product requirements.

Tempering and Cooling

Tempering gives moisture inside the kernel time to redistribute after a drying stage. The concept is:

A separate tempering silo is not required for every plant. The need depends on dryer design, moisture reduction, variety, drying strategy and capacity.

Cooling is also part of the process. Warm paddy should be cooled according to final grain temperature, ambient conditions, storage requirements and dryer design before longer-term silo storage.

Paddy Drying and Rice Milling Process

Why Pre-Cleaning and Wet Buffering Matter

Field paddy may contain impurities that interfere with grain flow, air distribution, dryer loading and heat transfer.

Rice mills often receive paddy irregularly, while the dryer needs a controlled supply. A wet grain buffer separates irregular receiving from stable drying and helps the dryer maintain more consistent operating conditions.

Storage After Drying

Drying quality can be lost if paddy is poorly handled afterward. A complete system may connect:

The silos provide a production buffer between dryer operation and rice mill consumption. They should be managed to prevent uncontrolled moisture absorption, temperature changes and repeated drying cycles.

How to Reduce Broken Rice Through Better Drying

1. Measure the initial moisture of each incoming batch.
2. Define a target moisture for the intended storage and milling process.
3. Avoid excessive drying intensity used only to maximize throughput.
4. Maintain uniform airflow and stable grain flow.
5. Use tempering where the dryer and grain condition require it.
6. Control cooling instead of treating it as an unrelated final step.
7. Verify discharge moisture and moisture uniformity.
8. Store dried paddy properly to prevent rewetting and deterioration.

Example: Rice Mill with Dryer and Silos

A project with a 15 T/batch paddy dryer, two 100 T silos and a 60 T/D rice mill can use the following process:

The dryer should be operated according to actual moisture and grain-quality requirements rather than only maximizing batch turnover.

Key Takeaway

Co-Grain evaluates paddy drying as part of the complete rice-processing system, including receiving, pre-cleaning, wet buffering, drying, conditioning, cooling, storage and milling.