Wood pellets are made by grinding wood waste into fine particles, drying it, and then forcing it through a press under high heat and pressure. The process transforms loose sawdust and wood scraps into dense, uniform cylinders that pack roughly 17.5 GJ of energy per tonne, making them far easier to store, transport, and burn than the raw material they came from.
What Goes Into a Wood Pellet
Most wood pellets start as byproducts from other industries. Sawdust, wood shavings, and small scrap blocks from sawmills and flooring manufacturers are the most common feedstocks. Hardwood flooring mills are particularly good sources because their waste is already clean (no bark or dirt) and relatively dry. More recently, producers have started using low-quality trees harvested from forest thinning and salvage operations, which are chipped and processed from scratch.
Both softwood and hardwood species work. Softwoods like pine are slightly more energy-dense, while hardwoods tend to produce denser pellets. The choice often depends on what’s locally available rather than any strict quality preference, since the manufacturing process standardizes the end product regardless of the starting species.
Grinding the Wood Down
Raw wood needs to be reduced to particles just a few millimeters across before it can be pressed into pellets. If the feedstock arrives as logs or large chips, it first goes through a chipper to break it into rough pieces. Those pieces then pass through a hammer mill, a machine that uses rapidly spinning metal hammers to shatter the wood against a screen. Only particles small enough to pass through the screen’s holes move on. The target size is typically in the low single-digit millimeters, fine enough that the particles will compress evenly and bond tightly in the press.
Grinding is one of the most energy-intensive steps in the process. Wetter wood requires significantly more energy to break down, which is one reason many producers prefer to work with waste that’s already partially dried from its previous industrial use.
Drying to the Right Moisture Level
Moisture control is critical. Finished pellets need to land between 8% and 10% moisture content, and the raw material has to be dried to roughly that range before pressing. Fresh wood can contain 50% or more moisture by weight, so drying often represents the biggest energy cost in the entire production chain.
Large rotary drum dryers are the most common equipment. Hot air passes over the wood particles as they tumble through a rotating cylinder, evaporating moisture over several minutes. Some facilities use waste heat from their own operations or burn bark and wood dust to fuel the dryers, keeping costs down. Getting the moisture level right matters for two reasons: too wet, and the pellets won’t hold together; too dry, and the natural binding agents in the wood won’t activate properly during pressing.
Pressing: Where Sawdust Becomes a Pellet
The heart of the operation is the pellet mill, a machine that forces dried wood particles through a flat or ring-shaped metal die perforated with small holes. Rollers compress the material against the die surface, and the pressure pushes it through the holes as continuous rods that are sliced to length by a blade on the other side.
What holds a pellet together isn’t glue. It’s lignin, a natural polymer that makes up roughly a quarter of wood’s dry weight and acts as the “cement” between wood fibers in a living tree. Under the heat and pressure inside the die, moisture in the wood helps lignin soften at around 100°C. Once soft, the lignin flows between particles and bonds them together. When the pellet exits the die and cools, the lignin resolidifies and locks everything in place. The exact softening point shifts depending on how much moisture is present and how much pressure the die applies, which is why operators fine-tune both variables throughout production.
Some raw materials, particularly certain softwood species or very dry feedstocks, don’t contain enough accessible lignin to form strong pellets on their own. In those cases, producers add small amounts of natural binders. Corn starch and wheat starch are common choices, typically mixed in at 1% to 5% of the total weight. Starch does double duty: it strengthens the bond between particles and lubricates the die, helping the compressed material flow through the holes more smoothly. Kraft lignin, a byproduct of the paper pulping industry, is another additive that boosts pellet hardness. A 4% addition of corn starch or kraft lignin has been shown to meaningfully improve density, hardness, and resistance to crumbling during handling.
Cooling and Hardening
Pellets leave the die hot, typically between 60°C and 95°C, and still carrying 12% to 17.5% moisture. At this stage they’re soft and fragile. A counterflow cooler handles the next step: ambient air is drawn up through a bed of falling pellets, pulling heat and moisture out simultaneously. The process takes about 4 to 15 minutes and brings the pellets down to within 5 to 8°C of room temperature and below 10% moisture.
Cooling isn’t just about making pellets safe to bag. If pellets are packed while still warm inside, the outer shell cools and contracts while the core stays expanded. That mismatch creates internal stress that leads to cracks and crumbling. Properly cooled pellets are hard, smooth, and resistant to breaking apart during transport and storage.
Screening and Packaging
After cooling, pellets pass over vibrating screens that separate out fine dust and broken fragments. These “fines” get recycled back into the production line. The intact pellets move on to storage silos or directly into packaging, which ranges from 15-kilogram bags for home stove owners to bulk truck loads for industrial power plants.
What Makes a Quality Pellet
Not all pellets are created equal, and grading systems help buyers know what they’re getting. The most widely recognized standard sorts pellets into grades based on lab-tested properties. Grade A1, the premium tier intended for home stoves and boilers, requires an ash content of 0.7% or less by weight. That means when the pellet burns, almost everything converts to heat rather than leftover ash you’d need to clean out. Durability, a measure of how well pellets survive handling without crumbling into dust, must hit at least 97.5% for the same grade.
Lower grades (A2 and B) allow progressively more ash and are typically used in larger commercial or industrial settings where higher ash production is less of an inconvenience. The raw material matters here: clean sawdust from indoor milling operations naturally produces lower-ash pellets than bark-heavy material from forest thinning, which is why feedstock selection and the initial screening of incoming wood are so important to the final product.
From Waste to Energy-Dense Fuel
The full process, from raw sawdust to bagged pellets, typically runs continuously in a single facility. What makes the whole thing work economically is the transformation in energy density. Loose, wet sawdust is bulky, hard to ship, and inconsistent. A tonne of finished wood pellets delivers about 17.5 GJ of energy in a compact, uniform form that flows through automated feeding systems like grain. For comparison, raw wood at natural moisture levels contains significantly less usable energy per tonne because so much of its weight is water. By driving off that water and compressing the remaining material, pellet producers turn a low-value waste stream into a standardized fuel that competes with fossil fuels in heating applications across North America and Europe.