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Feed pellet quality: what drives PDI and fines, and what to specify
Pellet quality is decided by the formulation, mash particle size, steam conditioning, die specification and cooling — and then by handling all the way to the feeder. Measure it with a stated pellet durability index (PDI) method and sample point, agree targets with your nutritionist and equipment supplier on your own diets, and compare pellet lines on conditioning control, steam quality, die options, cooler design and fines return. The Kansas State University figures below come from corn and soybean meal diets and are planning references only.
- Updated and sources checked: 23 October 2026
- 3 dated sources
- Free, no account or RFQ needed
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Questions this guide answers
- What is the pellet durability index (PDI) and how is it measured?
- Which conditioning temperature, moisture and retention time do mills aim for?
- What causes fines at the feeder?
- How does the die L:D ratio affect pellets?
- What should a pellet mill or pellet line RFQ ask?
What determines pellet quality
Kansas State University's Quality Feed Manufacturing Guide (Dunmire, Stark and Paulk, 2021) lists ingredient characteristics, the conditioning process, pellet mill configuration, pellet cooling and transport as the factors that influence the percentage of fines at the feeder.
The guide also puts the extra cost of pelleting at about US$5–6 per ton in its swine-focused context and notes that the benefits depend on maintaining pellet quality. Treat that figure as a dated US reference from the source, not a quotation for your site.
Sources: [1]
Steam conditioning: published planning references
Conditioning softens particles and lubricates the die. The references below are from one university guide for typical corn and soybean meal diets; your diets, species and heat-sensitive additives may need different settings, confirmed in supplier trials.
| Parameter | Kansas State reference | Why it matters |
|---|---|---|
| Total moisture of mash at the die | About 17–18%; above about 18% can plug the mill, depending on configuration | Moisture lubricates the die and helps particles bind |
| Conditioning temperature | About 180–200 °F (82–93 °C); lower for complex nursery diets (about 145 °F / 63 °C for high-whey diets) | Ingredients and additives that are sensitive to heat limit the temperature |
| Conditioner retention time | About 30–45 seconds | Longer retention improves heat and moisture uptake but can reduce throughput |
| Moisture added by steam | Roughly 1% for every 25 °F (about 14 °C) of temperature rise | Cold winter mash needs more steam, and gains more moisture, to reach the same temperature |
| Steam quality | About 97% vapour is high quality; at about 80% vapour the temperature reached per 1% added moisture falls by about 5 °F | Condensate traps and insulated lines protect steam quality |
Sources: [1]
Dies, cooling and liquid coating
The die's effective length divided by its hole diameter (the L:D ratio) sets how much resistance and compression the feed meets; a higher L:D gives more resistance. Kansas State describes carburised alloy dies as resistant to breakage and suited to higher-mineral feeds, and carburised stainless dies as giving the best pellet quality over time with moderately abrasive material and the least corrosion. It recommends recording tons per die and hours of use with each run.
Cooling should bring pellet moisture back to, or below, the moisture of the original mash, and an even bed depth in the cooler is described as one of the most overlooked points. The guide also notes that fat in the mixer is generally kept to about 1% or less to protect pellet quality, with more applied after pelleting, and that when more than about 3% liquid is applied before cooling it can be drawn off the pellet surface.
Sources: [1]
Measuring pellet durability (PDI)
PDI is the share of pellets that survive a standard mechanical test. Kansas State's quality assurance resources include procedures for the tumble-box method (standard and modified) and for a Holmen-type tester. Results from different methods are not interchangeable, so a PDI target in a contract needs the method, the sample point and the sample handling written next to it.
- State the method and sample point with every PDI figure
- Sample after the cooler when comparing lines; sample at the feeder when judging delivered quality
- Track fines returned to the pellet mill, because they use throughput and energy
Sources: [2]
Upstream: grinding and mixing
Particle size and mixing uniformity affect both pellet quality and nutrient delivery. Kansas State's batching and mixing guide cites a feed industry standard of a mixer coefficient of variation (CV) below 10%, rates 10–15% as good and above 20% as poor (after Herrman and Behnke, 1994), and gives corrective actions such as longer mixing times and equipment inspection. Ask suppliers how mixer uniformity will be tested at commissioning.
Sources: [3]
Indicative cost drivers
- Pellet mill size and motor power for your diet and pellet diameter, rather than a nominal rating
- Steam boiler, steam-quality equipment and the conditioner type
- Die and roller wear life at your mineral and fibre levels
- Cooler, crumbler, screener and fines-return conveying
- Post-pellet liquid application for fat or heat-sensitive enzymes, and its metering
- Energy per tonne and maintenance labour
- Throughput lost to downtime and die changes
Cost drivers only — FeedMatch does not publish prices. Request scoped quotations on the same delivery basis.
Efficiency and sustainability considerations
- Kansas State notes that conditioning at too low a temperature increases frictional heat at the die, uses more energy, reduces throughput and increases die wear.
- Fewer fines means less feed recirculated through the pellet mill.
- Logging tons per die and pelleting data helps plan die changes instead of running worn dies.
Risks to manage
- PDI targets without a method or sample point
- Rated capacity quoted on an easy diet rather than yours
- Heat-sensitive additives added before conditioning without stability evidence from the supplier
- Uneven cooler bed depth leaving warm, moist pellets that can spoil in storage
- Tramp metal causing uneven die wear or damage when magnets are missing or not cleaned
Next steps, tools and related guides
- Pellet mill buyer guide
- Pellet coolers and dryers
- Example RFQ: pellet line and mixer
- Feed-mill energy calculator
- Feed-mill capacity calculator
- Plan an equipment project
Send one brief. FeedMatch reviews it, contacts suitable suppliers and presents organised responses — buyer use is free. The US$250,000 minimum applies only to plant and equipment projects, not to ingredient or recurring feed supply.
Sources
- Kansas State University — Quality Feed Manufacturing Guide: Pelleting (Dunmire, Stark & Paulk) · University guide · 2021
- Kansas State University — Feed manufacturing quality assurance guidelines and forms (incl. pellet durability and mycotoxin test procedures) · University guide · Resource page
- Kansas State University — Quality Feed Manufacturing Guide: Batching and Mixing · University guide · Quality Feed Manufacturing Guide series
Document dates are the publishers' own. Laws and guidance are amended — use the current official text. FeedMatch's guides are decision support, not legal, nutritional or engineering advice.
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- The buyer needs the request structured (capacity, animal category, feed form, location, timeline) before contacting suppliers.
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Common questions
What is a good pellet durability index?
Why do pellets break down between the mill and the feeder?
What should a pellet mill quotation include?
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