The lives of sheep are such that all wool contains some amount of vegetable matter, or VM. Much of the VM in wool is removed when the wool is washed and carded. If the wool is also combed, even more VM can be removed. But probably not all.
In order to get out the VM that remains, most commercially-processed wool undergoes a process called *carbonizing* to remove vegetable matter. Carbonizing involves a number of steps. First, the wool is soaked in a solution of sulfuric acid to weaken the structure of the VM. It is then dried in a 100-104 C oven, during which the sulfuric acid solution becomes more concentrated, transforming the VM to carbon. The fibers are then passed through rollers to crush the carbonized VM, and then through mechanical agitators to remove the residual dust. Then the fiber is rinsed in water, soaked in a sodium carbonate solution to neutralize the acid, and washed again.
If it the process is not carefully monitored, excess acid during carbonization may weaken or damage the wool fibers. The process requires large amounts of water; it may expose mill workers to harmful sulfuric acid fumes; and sulfuric acid may be released in the mill’s effluent. Some people are allergic to the chemical residues of the process that may remain on the wool.
Most small mills do not carbonize, so our Clun Forest, Rambouillet and Suffolk yarns are spun from wool that has not been carbonized. The fact that they’ve been more gently processed than most yarns contributes to their particular character and handle, but it also means that you may find some VM in them. I do my best to pick out anything I notice while dyeing and reskeining the yarn; anything that remains can be removed as you knit.
Our Sustainable Merino yarns are carbonized, so they are good choices if you're put off by VM.
I would love to hear from you about how you feel about carbonizing, VM, and Sheepspot's non-carbonized yarns. Let me know in the comments.