Wood pellets are made primarily from compressed sawdust and wood shavings, the byproducts of sawmills and wood processing facilities. Most of the world’s wood pellets come from these waste streams rather than from whole trees. The raw wood is ground into fine particles, dried, and then forced through a die under high pressure, which heats the material enough to activate its natural binding compounds. The result is a dense, uniform fuel with about 6% moisture content, roughly 7,750 BTU per pound.
The Raw Wood Inside a Pellet
Sawdust is the single most common ingredient. Sawmills generate enormous quantities of it, and pellet manufacturers buy it in bulk. Wood shavings, planer dust, and chipped logging residues also go into the mix. The wood particles are ground to a size between 0.2 and 1.5 millimeters before they enter the pellet press.
Pellets can be made from hardwoods like oak and maple, softwoods like pine and spruce, or blends of both. Softwood species actually carry slightly more energy per pound (about 9,050 BTU) than hardwoods (about 8,600 BTU) because of the natural resins they contain. In practice, the difference narrows once the wood is compressed into pellet form, but softwood pellets do tend to burn a bit hotter.
Bark content matters. Bark contains roughly five times more mineral ash than the inner wood, and the more bark in the mix, the more ash you’ll need to clean out of your stove or boiler. Small amounts (5 to 10 percent) don’t cause problems, but pellets made entirely from bark can leave behind fused, glass-like ash deposits called clinkers that clog stoves. Premium pellets keep bark to a minimum.
How Lignin Acts as Natural Glue
Wood pellets hold their shape without requiring much, if any, added glue. The secret is lignin, a tough polymer that makes up about 25 to 30 percent of wood by weight. In a living tree, lignin is what gives the cell walls their rigidity. During pelletization, the friction of wood being forced through narrow die holes generates enough heat and pressure to soften lignin and cause it to flow between particles. When the pellet exits the die and cools, the lignin hardens again, forming solid bridges that lock the particles together.
Water plays a supporting role. A small amount of moisture (the raw material typically sits at 10 to 12 percent moisture) acts as a plasticizer, helping lignin and another wood compound called hemicellulose soften more easily under pressure. Too little moisture and the lignin won’t activate properly; too much and the pellets fall apart. The target is a narrow window, and manufacturers monitor it closely. A well-made pellet ends up with a density of about 1,050 to 1,100 kilograms per cubic meter, roughly twice as dense as natural wood.
Additives Some Manufacturers Use
Most residential wood pellets contain nothing but wood. However, some manufacturers add small amounts of binding agents to improve durability, especially when the raw material is dry or has low lignin content. Common additives include corn starch, wheat starch, and other plant-based starches. These are natural, renewable, and burn cleanly. Lignosulfonate, a byproduct of paper manufacturing, is another binder used in some pellet production.
What you won’t find in certified residential pellets is recycled construction wood, painted lumber, or furniture scraps containing chemical adhesives. Several countries ban the use of chemically treated wood waste in pellet production, and quality certification programs enforce strict limits on contaminants. While some research has explored making pellets from glued wood waste (and found that small amounts of adhesive don’t ruin the fuel properties), these products generally fall outside the standards for home heating pellets.
Grilling Pellets vs. Heating Pellets
Not all wood pellets are interchangeable. Heating pellets are designed purely for energy output and can contain 100% softwood or hardwood-softwood blends. Pine is common because it burns hot and is inexpensive. These pellets may also include bark, leaves, and other impurities that don’t affect heating performance but would be a problem if you were cooking with them.
Food-grade grilling pellets are made exclusively from hardwoods like hickory, cherry, mesquite, or apple, chosen for the flavor they impart to food. They’re manufactured under tighter controls to exclude softwood resins (which leave a bitter taste) and contaminants that could pose a health risk when ingested through food. Using heating pellets in a pellet smoker is not recommended, even if they look identical.
What Quality Grades Mean
In the United States, the Pellet Fuels Institute (PFI) certifies pellets into two main grades based on ash content, which is the best single indicator of purity. PFI Premium pellets must contain no more than 1.0% inorganic ash by weight. PFI Standard pellets allow up to 2.0%. In Europe, the ENplus system uses a similar tiered approach with A1 being the cleanest grade (0.7% ash limit) and A2 allowing up to 1.2%.
Lower ash content means less bark, less dirt, and fewer minerals in the raw material. For homeowners, premium-grade pellets mean less frequent ash cleanout, fewer clinker problems, and generally smoother stove operation. Standard-grade pellets cost less and work fine in larger commercial boilers that are designed to handle higher ash loads, but they can be more trouble than they’re worth in a small pellet stove.
Why Pellets Outperform Firewood
The manufacturing process is what sets pellets apart from the trees they came from. Air-dried firewood typically contains about 20% moisture, while finished pellets sit at around 6%. That difference is significant: water in wood absorbs heat as it evaporates, so wetter fuel wastes more energy. Combined with their higher density, pellets deliver roughly 7,750 BTU per pound compared to the lower effective output of cord wood. They also burn more consistently because every pellet has nearly the same size, moisture content, and density, which allows automated stoves to regulate their fuel feed precisely.