“Clinker” is the byproduct of burning wood pellets in a controlled chamber pot in your pellet grill. Because the pellets are in the confined area of the burn pot, the ash can build up forming a crust that would normally be mixed in the ash pile and not seen. Because your pellet grill has a fan that blows air into the burn pot the lighter ash is blown out and what is left behind is melted together by the high heat and fire forming a cluster that is called “Clinker”. 
 
Pellets that use more bark to wood ratio have a bit more of this byproduct which is mainly derived from the bark. But why is Clinker actually GOOD to see? Clinker demonstrates the quality of a pellet as having more bark to wood ratio. Bark has much more flavor and also burns much hotter than the heart wood. And that is why Knotty Wood BBQ pellets are SPECIFICALLY made from the WHOLE tree to include the bark! You’ll know when its PURE orchard wood that is being burned if Clinker is what is left behind.