I have been dyeing coffee yarn over the last few days. It is a multi-day process and I will do my best to give you an overview of the steps of how it is done.
You need to start with yarn in a skein with several (I think at least four is best) ties to keep the yarn from getting tangled, but not so tight the dye can't penetrate. Yep, forgot a picture of that part. WOG stands for Weight Of Goods, which is the dry weight of the yarn you want to dye. After weighing your yarn it needs to be soaked in cool water to get it completely wet. It is best to then squeeze it out to help make sure the air is all out so the water can get in. Then the yarn needs to have a mordant applied. Since I was dyeing wool with a "natural dye" I used 10% WOG alum and 5% cream of tarter. I have also dyed wool with what is known as "acid dyes" in which case the mordant is citric acid. Kool-aid is an acid dye and already has the citric acid mixed into it, so you don't need to add extra. I have also dyed cotton and rayon, but that is a totally different process and needs a different kind of mordant.
So to apply the mordant you need to place your pre-wetted yarn (or loose fiber if you want to do fleece) into a dyeing dedicated pan (I have a water-bath canner just for this purpose.) Then you need to add enough cool water to cover the yarn and also have free movement for gentle stirring. Then measure out your mordants, mix them with a small amount of hot water to dissolve and add that to your yarn in the pan. Stir gently so as to not tangle up your yarn. Slowly bring to a simmer, cover, and then lower the heat to just below simmer and keep it there for an hour. Gently stir it occasionally with out tangling up your yarn. Turn off the heat and let cool overnight. If you can let it sit for twenty-four hours it is best, but twelve is ok.
Next comes the dye bath solution preparation. This also takes awhile, so you can do it at the same time as your mordant bath, just in a different pan. Since I was using just coffee, I went a head and used a pan I also use for cooking. I DO NOT do this for any other dye bath I make. Not even onion skins. Had I been able to locate the box with the rest of my dye pots in it, I probably would have used a non-cooking pot. So I took ground coffee at 100% WOG and put it into the pan, added water to make a soupy looking mess. You need enough water to make coffee, though it is concentrated. How ark your yarn turns out is based on the dye to fiber ratio, not the amount of water involved. So you need to bring this to a boil, and then reduce to a simmer for about thirty minutes. If you want to make it an hour it is ok. Then you turn off the heat and let it sit overnight to steep. After about twelve hours or so, I strain the coffee grounds. I put the liquid in one container and put the grounds back into the pan, add more water, and bring to a boil again. This time I only simmer for ten minutes or so and then let it steep and cool down. (All of this can be going on while the yarn is in the mordant bath.) Strain again and add this coffee to the original coffee. I usually do one more extraction from the grounds at this point, but that will depend partly on how dark the liquid is looking from the last extraction (and how impatient I am getting). The straining is messy, but important. No matter how well you strain your coffee, you will have some end up in your dye bath, but you want to keep out as much as possible. Take my word for it, coffee grounds stick to yarn a lot more than you would ever guess. I use a sieve and then a coffee filter.
Next comes the actual dyeing process. After letting your yarn sit in the mordant bath for twelve to twenty four hours, you need to drain it and gently squeeze out the excess water. (If you use just alum and cream of tarter it is safe to pour this down your drain, regardless of having public sewer or a septic system.) You can now dye it right away, or you can hang it up to dry (As in if you want to mordant several skeins to dye, but only want to dye some with coffee and want to do some with onion skins or something else.)
After draining and squeezing out your yarn, you may put it right back into your empty dye exclusive pan. DO NOT USE A COOKING PAN FOR THIS STEP. Add your coffee solution, which should be at room temperature. Add enough cool water to cover the yarn and make it easily float about. Gently bring to a simmer, reduce heat to just below a simmer, and cover. Keep it just below a simmer for an hour, gently stirring occasionally. Turn off heat and let cool and steep overnight. Again, twenty-four hours is great, but twelve is ok.
For informational purposes, if you do this, your house will smell like hot wet sheep, and then like hot wet sheep and burnt coffee. Not really the greatest smell, but I did tell Hubband at least it smelled like clean sheep, not like the ones he worked with on the ranch when he was younger.
Tomorrow you get to see what it looks like when it is all dried out and ready to go.
Oh, and in case you are wondering where I learned about all this? It was in college as part of my B.S. in Anthropology.