Washing grease fleece is a task that every spinner will encounter at some point in their spinning career. There are probably as many methods of washing wool as there are spinners yet many of the methods I’ve seen mentioned will simply not do a good job of it.
The keys to washing wool are first, an understanding of grease fleece and second, an understanding of how grease wool reacts to water, heat, and soap.


SUINT:

Grease wool fibers contain both lanolin (wool fat) and suint, which is the secretion of the sheep’s sweat glands. It is a chemical compound containing at least 18 different amino acids, potassium salts, and soapy organic salts. The suint content of the fleece is what traps and holds dirt, which makes wool fibers difficult to process and draft and so it’s best to wash this out before processing.

Besides trapping dirt in the fleece, suint, adds weight to yarns spun in the grease. It’s much, much harder to wash this out of yarns spun in the grease than it is to wash it out of the fleece. All of the components of suint are soluble in cold water and, in fact, will form their own washing agent as they dissolve. Cold washing removes both the suint and the dirt it traps.

Recipe for Cold Washing:
Mesh laundry bags or nylon netting or screening to contain and support the fleece.
Grease fleece.
Large tub of cold water
Large tub of tepid water
It is best to work with smaller sections of fleece at a time. Too much fleece crowds the wash tub preventing the fleece from becoming totally saturated. Place the fleece into the
mesh bags or sew it up in the nylon netting or screening. Make small bundles. Fill the large tub with cold water and gently push the fleece packets down under the water. Do not add any soap or detergent – the salts in the grease wool will dissolve and form their own cleansing agent After soaking, remove the fleece bundles. Fill the tub with tepid water and soak the bundles for half an hour. This soak removes any residual stickiness from the potassium salts. This washing method removes NO lanolin. Use it for removing dirt and suint from fleeces you wish to spin in the grease or as a pre-wash for very dirty fleeces.


LANOLIN OR WOOL FAT:

Lanolin or wool fat is produced by the sebaceous glands in sheep. Each wool follicle has it’s own gland so each wool fiber is coated with lanolin as it grows. Some spinner like to wash all of the lanolin out of the wool before processing it, others prefer to leave some degree of lanolin in the fleece as an aid to spinning. If all of the wool fat is washed out prior to spinning, it may be necessary to add some oil back to the wool to prevent static electricity and enable the fibers to hold together during the drafting process. Note, however, that any lanolin left in the fleece will have to be washed out after it’s spun into yarn.

Heat softens and melts lanolin. At 70 degrees F., lanolin will be soft enough to start moving under the force of gravity. This fact explains why luster long wool fleeces sometimes seem to have more lanolin at the tips of the locks than at the butt ends.

At 110 degrees F, lanolin starts to melt. The hotter the temperature of the water is, the faster the melting, but only to a point. Too hot of temperatures and the scales of the wool will start showing signs of damage. This is especially apparent with Luster Long Wool fleeces, which will start showing signs of damage and loss of luster at 95 degrees F. Mabel Ross, writing in her book, The Essentials of Yarn Design for Hand Spinners comments on page 21: "Note that luster wools will have their luster impaired if washed at a higher temperature than 95 F."

Nikki Wyscaver has developed an easy experiment for seeing how water and temperature affect the lanolin in grease wool. Simply take small locks of grease fleece and dip them into small pots of water at different temperatures. No soap is needed, just watch how the lanolin moves at the different temperatures. Try dips at 90, 100, 110, 120, 140, and 160 degrees. This will give you a good idea of just how hot of water you want to use to leave a controlled amount of lanolin in your wool. Also try this with Luster Long Wool locks and compare them once they are dry. The difference in luster will be apparent.