Pellet stove heating is so efficient because wood pellet fuel is uniform. However, there are natural and perfectly acceptable variances in both color (and sometimes length) within wood pellets.
Much like snowflakes – no two wood pellets can be exactly the same. Wood pellets can have a variety of colors, depending on the primary species of wood used. Common hardwoods used to make pellets include Maple, Oak, Birch, Cherry, and Beech. Typical softwood raw materials used to manufacture wood pellets are Hemlock, White Pine, Spruce, and Fir. The wood species for the raw materials used to produce either hardwood or softwood pellets is the principle reason for the variety of colors. Pellet colors can range from a pale blonde, to a warm reddish brown, to a dark walnut.
Don’t be alarmed if the ton of your favorite wood pellets delivered to your home has a slightly different hue than the same brand delivered last year. This just means the batch of wood material used to make the wood pellets had some color variation. This is completely normal when dealing with 100% natural raw materials.
While a spectrum of colors is perfectly natural, wood pellets should generally not be darker than a cup of black coffee. Aside from torrefied pellets – an excessively dark wood pellet color may indicate that bark was mixed into the manufacturing process. Those pellets will likely have a high ash content.
Torrefied wood pellets are made from wood material that has been roasted at high temperatures in an oxygen-deprived environment. The torrefaction process creates super durable, low ash wood pellets.
Regarding variations in pellet size – the length can vary from 0.25 to about 1.5 inches. Most pellet stoves will work just fine within this normal range.
Finally, all wood pellets will have a uniform diameter due to the pellet manufacturing process. The diameter typically ranges from 6mm to 8mm. (See: How are Wood Pellets Made?)