Scoured Wool

A scour line moves wool through a sequence of bowls, each washing and rinsing, with squeeze rollers between them and a dryer at the end. The wool grease and suint dissolve or emulsify away, and dirt and sand fall out. What emerges is loose clean fibre — visibly and functionally different material from what went in, dramatically lighter, and ready to be carded.

The fibre itself is not transformed. Scouring is a cleaning operation, not a modification: mean fibre diameter, staple length, and the intrinsic character of the wool arrive at the scour already fixed by the animal and cannot be improved by washing. This is the essential point about the product — scouring reveals the fibre that was always there, and what it cannot do is make poor wool good.

Yield is the proportion of a greasy lot recovered as clean fibre, and it is the number that connects the two commodities. Because it is measured on samples before the greasy wool is sold, the trade can price a bale of dirty fleece against the clean fibre it will actually deliver. Scouring then realises what the measurement predicted.

Yield varies substantially with the environment the sheep were run in — dusty, dry country produces heavier, lower-yielding wool than clean pasture — which means two bales of identical greasy weight can be worth quite different amounts. That is not a market imperfection; it is the market correctly pricing what is in the bale.

Scouring is aqueous, so it removes what water and detergent can take away. Vegetable matter is not one of those things. Burr, seed, and plant fragments largely survive the scour and must be dealt with afterwards — mechanically during carding and combing, or chemically by carbonising, which uses acid to char the plant material so it can be crushed out. Carbonising works but is aggressive, and it is a reason a high vegetable-matter lot is discounted at the point of sale rather than treated as a problem for later.

Foreign fibre is the other survivor, and a worse one. Polypropylene from twine or packaging, and dark fibre from other animals, pass through scouring untouched and stay in the wool through spinning, appearing as visible faults once the fabric is dyed. Because no downstream step reliably removes them, contamination prevention is a farm-and-shed discipline that the rest of the chain depends on entirely.

Clean wool is strongly hygroscopic and its mass changes with the humidity around it, so trading it on as-is weight would mean trading water. The industry resolves this by transacting on a defined moisture basis, with conditioned weights established by testing authorities — an arrangement that is unusual among agricultural products and reflects how precisely the wool trade quantifies its material.

Beyond that, scoured wool is a durable, storable product: baled, warehoused, and shipped without refrigeration or urgency, needing only to be kept dry and free of contamination. Scouring is also water- and energy-intensive and generates a heavily loaded effluent, from which wool grease is recovered and refined into lanolin — a genuine recovered stream, but one that belongs to the scouring process and is not modelled here as a pathway.