As part of the shift towards circular agriculture and to reduce competition for arable land between food and feed, an increase in the use of fibrous co-products in livestock feed is expected. However, the impact of these raw materials on the pellet manufacturing process is not well understood.
To address this knowledge gap, Wageningen University & Research (WUR) launched a public-private collaborative project four years ago. This project aimed to support the use of more fibrous co-products in feed and enhance the sustainability profile of the European feed and livestock sectors.
Process engineers and PhD candidates Richard Benders and Tom Bastiaansen have been key contributors to the project. Their research focuses on understanding and optimizing extrusion-like processes for pressing co-product materials into pellets using residual streams from the human food and bioenergy industries.
Pellet manufacturing involves conditioning ground and mixed feed ingredients (mash) with steam, compacting the mash by pressing it through a die, and then drying and cooling to remove excess moisture and heat. These processes alter the physicochemical properties of feed particles, forming the necessary inter-particle bonds to produce high-quality pellets that do not break or disintegrate during transport or storage. The goal is to produce these pellets with minimal energy input to limit economic and environmental costs.
The researchers conducted pilot-scale trials and consulted with feed manufacturers, feed processing technology providers, and other industry stakeholders.
"We also used state of the art imaging techniques like x-ray tomography (CT-scans) and electron microscopy, combined with physical modelling techniques in order to understand the pelleting process and bond formation at a fundamental mechanistic level," Benders told FeedNavigator.
Temperature and time responses
Their findings indicate that including fibrous co-products in feed instead of cereals required generation of further insights into the pellet binding properties and that different fibrous co-products, such as apple pulp, chicory pulp, citrus pulp, faba bean hulls, and others, each impact the pelleting process differently. “The key variables in the process are temperature and time, which vary depending on the specific ingredient,” said Benders.
For instance, ingredients with high oil content have low friction inside the die and may require more steam for binding, while very fibrous products with low oil content and high friction may benefit from reduced steam and added water, he explained.
“These adjustments help optimize the pelleting process for cost, sustainability, or quality, depending on the stakeholder's priorities—whether it's farmers seeking certain pellet quality, feed mills aiming for high throughput at low cost, or considerations of the carbon footprint and animal growth rates.”
The researchers used novel analytical methods to better characterize pellets, examining the temperature and time responses of individual ingredients. Understanding when ingredients transform from brittle to sticky states helps optimize the pelleting process, added Benders.
Future research will focus on the differences in inter-particle bond formation among co-products and the required conditions for successful pellet manufacturing.
Sharing the knowledge
The project's findings have been actively shared with feed professionals through workshops and e-learning modules organized by the Feed Design Lab and Aeres Training Centre International.
