First, I added extra ties on the skeins to keep them neat and tidy during the dye process, then soaked them in a tub of tepid water and vinegar for 30 minutes.
While the skeins were soaking, I prepared my dye. I'd been collecting small quantities of coffee beans over the last several months; my husband works at a local coffee roaster, so we always have an overabundance of coffee beans in the house. Since they are no longer considered "brew-worthy" a few weeks after their roast date, I decided to use them for dyestuffs before sending them to their ultimate resting place, the compost heap.
I can't say I was terribly scientific with this part of the process - basically, I ground all of the beans I had available (I'd guess about a quarter-pound) and split them into two groups to be brewed in the French press for about ten minutes each. When they were finished brewing, I strained the coffee grounds out and poured the resulting mixture in to the crock pot to cool down.
Once the dye was cool and the yarn was soaked, I gently squeezed the excess water out of the skeins and transferred into the dye bath, adding a little extra water to make sure everything was submerged. I let the skeins slowly heat up in the crock pot and cooked them for two hours, being careful not to boil (aka felt) the wool.
I allowed the yarn to cool down overnight, rinsing the excess dye from them in the morning before hanging them to dry.
The resulting skeins are a warmer, reddish-brown color that is pretty, though I wish they were a tad darker. According to my most unscientific findings and calculations, that would probably require at least a half-pound of coffee to be used, maybe even a full pound!
All in all, I'd give coffee dyeing a second try; preparation and cleanup was quite easy, plus it made the house smell great!