Kempink Methodology
The standard for reproducible PDI measurement
trusted by the pellet production sector.
PDI: The number that determines whether your pellets hold.
Pellet Durability Index (PDI) is the standard measurement for the mechanical durability of pellets under controlled test conditions. It expresses the percentage of a pellet sample that remains intact after a standardised tumbling and mechanical stress test. A PDI of 98.0% means that 98 out of every 100 grams of pellet sample survived the test as intact pellets.
A PDI value is only meaningful if the method that produced it is reproducible. That is the core problem the Kempink methodology was designed to solve.
PDI is the central quality parameter in pellet production because mechanical durability determines what happens between the press and the end user. Low-durability pellets generate excess fines during handling and transport. Those fines cause dust at the customer, reduce combustion efficiency, compromise feed intake in animals, and trigger non-compliance with the quality standards your buyers and certifying bodies require.
One pellet, one reliable value. The problem with PDI measurement.
“PDI is known across the sector — but a PDI value is not a fixed fact. The result varies by measurement method, by sample, and by operator. It is precisely that variability that costs you certainty.”
Source of variability
How it occurs
Consequence
Measurement method
Different tumbling geometries, rotor speeds, and sample volumes produce different results. A PDI from one instrument is not directly comparable to a PDI from another unless the methods are correlated.
Results cannot be reliably compared across sites, suppliers, or audit cycles.
Sample preparation
If production fines are present in the sample, they inflate the apparent fragility. A poorly prepared sample shows lower PDI than the actual product warrants.
The measured PDI reflects sample quality, not product quality.
Operator dependency
Manual sieving, timing of test start, and sample loading all introduce human variability. Different operators produce different results from the same product.
Results are shift-dependent and cannot be used as a reliable baseline for quality decisions.
How the Kempink test eliminates variability.
The Kempink test removes variability by making the measurement consistent and repeatable: an automatic start, a control system that keeps every test cycle exactly identical, and the automatic sieving of fines so that every test starts with a clean sample. The result is a traceable, reproducible PDI value that you can compare batch to batch — and that provides the substantiation your quality system requires.
Design element
Mechanism
Effect on variability
Automatic start
The test cycle starts automatically the moment the sample is loaded. There is no manual trigger, no operator timing, no start sequence that varies by user.
The test cycle starts automatically the moment the sample is loaded. There is no manual trigger, no operator timing, no start sequence that varies by user.
PLC with frequency controller
A programmable logic controller combined with a frequency controller maintains exact drum speed throughout the test cycle, regardless of load or power fluctuation.
Test-to-test variation in drum speed: eliminated
Automatic fines sieving
Production fines are automatically removed before the test begins. Every test starts with a clean batch of intact pellets only — not with a sample contaminated by the fines the measurement is supposed to detect.
Sample preparation variability: eliminated
Correlated to the standards your sector certifies to
Animal Feed
The recognised standard for pellet durability testing in the animal feed industry. GMP+ B1 and GAFTA quality management requirements for pellet quality documentation are assessed against this standard. Kempink results are directly correlated to ASAE/ASABE S269.5, making them usable as the measurement basis for GMP+- and GAFTA-compliant quality documentation.
ASAE/ASABE S269.5
Wood Pellets & Biomass
The recognised international standard for mechanical durability testing of wood pellets (current edition, published March 2025; supersedes ISO 17831-1:2015). ENplus A1 (≥98.0% DU) and ENplus A2 (≥97.5% DU) certification requirements are referenced to this standard. Kempink results are correlated to ISO 17831-1:2025, making them directly applicable to ENplus compliance documentation.
ISO 17831-1:2025
A Kempink PDI result is not a proprietary measurement. It is a result that speaks the language of the standards your buyers, certifying bodies, and auditors already rely on.
Built for the standards your sector requires
Rooted in the Industry WEMO-techniek has been developing automated sampling and testing solutions for bulk solids since the late 1990s. We do not just supply equipment. We understand grinding, mixing, pelleting, cooling, and storage from the inside.
From a single tester
to a sector standard.
The Kempink test methodology was developed by Sjaak Kempink in response to a fundamental frustration with existing PDI measurement practice: results were unreliable, operator-dependent, and not reproducible across sites. The goal was a method that would produce the same result regardless of who ran the test.
In 2012, the first Laboratory Kempink Tester was introduced — a commercially available instrument that implemented the Kempink methodology in a laboratory setting. Its design — automatic start, PLC-controlled test cycle, and automatic fines sieving — made it the first PDI tester that could produce consistent, operator-independent results.
The Kempink PDI tester has since become the reference instrument trusted by feed manufacturers and wood pellet producers across Europe and beyond. The same methodology that made the Lab Tester the sector standard is the foundation of every WEMO inline measurement system.
The Kempink test is recognised across the sector as the reference the industry relies on.
Kempink methodology in
every WEMO system.
All four WEMO products are built on the same Kempink test methodology. The measurement principle, standards correlation, and result reproducibility are identical across the portfolio.
Laboratory Kempink Tester
PDI measurement in the laboratory — batch validation and calibration reference
The original implementation of the Kempink methodology. Operator-independent, correlated to ASAE/ASABE S269.5 and ISO 17831-1:2025. Direct purchase.
Certified PDI measurement
Correlated to ASAE S269.5 & ISO 17831-1
Batch validation & traceability
Inline Kempink Tester
Continuous PDI measurement on the production line, per batch
The same Kempink methodology, running automatically on your pressing line. Results to MES in real time. Delivered as Quality-as-a-Service.
Continuous inline measurement
Real-time process data
No production interruption
Inline Kempink Tester Ctrl+
Predictive PDI management: measurement, prediction, and adjustment recommendations
The Kempink methodology extended with a predictive intelligence layer. Up to every five minutes per pressing line. Delivered as Quality-as-a-Service.
Predictive durability insights
Recipe-based adjustment recommendations
QaaS — no capital investment
Inline Packing & Coding System
Automated retention sampling alongside PDI measurement
Automated sample collection, packaging, and direct batch coding. Closes the quality loop with physical, audit-ready documentation. Delivered as Quality-as-a-Service.