After you finish spinning a skein of yarn, it's important to set the twist. This helps the energy in your yarn relax and it also helps the yarn bloom which shows you how a finished object made with your yarn will behave after it is washed. You don't want any surprises to show up.
I started out with these 3 skeins. As you can see they still full of twist energy. I always overply my yarns and this is the result I end up with. (My very first skein of handspun yarn which I spindle spun and plied on a wheel was very "balanced looking" when I was finished, but when I went to knit with it, it was very underplyed = lesson learned).
My samples are: Humbug Finnish, Merino/Silk and Finn wool.
**Its very important to tie your skeins in at least 3 places. This prevents tangles and tears
Fill your basin/sink with warm water and a bit of Soak wash. Place your skeins in the water and gently submerge them to release any air bubbles. Make sure the skeins are completely wet. Let the water & wool wash flow through your fibres for at least 15 - 20 minutes.
Now for the fun part - thwacking! I find this really helps my skeins relax and it releases a ton of built up energy. Take the damp skein out of the salad spinner and hold it with your arms outstretched. Bring your hands close together and then very quickly open your arms wide and your skein will make a slapping sound. I have demonstrated this step in this quick video:
You can also hit your skein along the side of your tub or another hard surface.
Hang your skeins in a warm place to dry. *This step goes really fast if its nice and hot and you can hang these outside. You can see how much they have relaxed compared to the first photo.
Now after all of this, I should also say, that your don't HAVE to do this. There are no spinning police. If you don't want to set the twist, that's fine, just keep in mind that your yarn will behave differently when working with it. If you want an energized yarn then perfect :)
Let me know if you have any questions and happy spinning!