Good wool and Bad wool

Not all wool is the same. There is the difference between breeds and the age of the sheep, in addition, the time of shearing and the environment that the flock is raised also changes the fleece. If you get raw fleece you will have a different process of turning this into yarn than if you buy tops, roving or batts.

A single animal will produce different qualities of fleece. The fleece near the head (collar) and along the lower ribs of the sheep (skirt) are probably the best parts. The top of the back is prone to matting due to the rubbing of the animal while the back end is usually decent quality wool but needs a lot of cleaning.

At the end of the selection process, you want fibres that are fine, long, clean, free of slubs and of consistent length. All of this even before you touch a wheel or even starting washing the fleece.