Studio Reference: Wool Scouring and Temperature

How hot does the water need to be to effectively scour wool?

Use water that can be heated and sustained between 140-160 degrees for the entire duration of the soak. No matter which soap you use, or how many times you soak your wool, lanolin will not dissolve or it will re-solidify under 140 degrees. 


Boiling Water

This is a common method for scouring outside which I observed with awe several years ago. The details vary from person to person, but during my observation, this method was done using 10 gallon stock pots over a propane camp stove. The water was brought to a rolling boil, 220 degrees, then taken off the stove, while a second pot (for the next fleece) began heating. 

After dissolving one full cup of powdered laundry soap into the pot, roughly five pounds of greasy wool (a durable breed probably Dorset) were stuffed inside the boiling soapy water. Wool has an amazing quality of absorption which makes it seem miraculous that the pot does not overflow.  

The pot full of wool was then insulated with old bath towels wrapped around top, bottom, and sides, then left to sit for twenty minutes. 

At the end of the soak, the water was poured out onto the ground like draining a can of beans, and the remaining wool was dumped into a spin dryer. This handy tool makes it possible to get a really good extraction while working outdoors. A washing machine offers the same, but obviously is less portable. 

That was it! This fleece was then spread out over a clean homemade skirting table to dry in the sunshine, which it did very quickly because it was still hot coming out of the spin dryer. Afterwards it felt clean, smelled great, and didn't feel greasy when hand picking. 

I have questions about the lack of rinsing of this method. Residual soap can deteriorate fiber over time. I also do not believe this method would work well for fine wools that are more delicate and reticent to release their grease. There is no doubt, however, that for medium to coarse fiber it was the most efficient for its effectiveness. I should also say it has been quite some time since I observed this method, and my insights into processing have changed quite a bit since then. I'd like to try this again sometime and see if my opinions still stand. 


Similar to the method above, but more commonly used indoors, this method starts with boiling a large pot of water on the stove. The boiling water is added to a prepared basin (sink, pot, bucket, tub, old washer, etc.) of hot tap, being careful to measure and maintain an adequate temperature closer to 160 degrees. There will be some cooling during the soak, so you don't want to start at 140, and loose effectiveness to cooling. 

The same elements of insulating, soaking, and extracting are applied in a range of diverse methods which we can explore in a future post.  I'd love to hear about your best practices. Please feel free to share in the comments below. 

Residential and Electric Hot Water Heaters

Sometimes you can manually change the temperature on your hot water heater at home to meet the needs of scouring. If you do this BE CAREFUL to put it back the way it was so that you or your loved ones don't end up washing their hands or showering in scalding water. 

Check your heater to see what range is safe to use with your particular model. Some residential water heaters are not made to go high enough to scour wool, so please do careful research on this one. 

If you intend on using this method with your washing machine as the basin, don't forget to consider the path of waste water especially if you are on a septic. We'll talk more about this in a post about waste water. Shoot me any specific questions you might have by email or in the comment section below. 

On-Demand and Propane Hot Water

Propane is more effective than electricity at heating water efficiently for scouring. Natural gas is not an option in my location, so I chose a propane, Takagi outdoor tankless water heater for the mill, and I have been very happy with it. It may not make sense to install a new water heater just for washing wool. However, if you pay for processing regularly, scour a significant amount of wool annually, or live near others who do, it might be rewarding in the long run to invest in an efficient or even cooperative scouring set-up. 


Fiber Types

Efficiency in scouring is most critical when working with fine wools. When a greasy fine fleece is immersed in hot water, the locks cling to each other more densely than a coarser fleece. When it comes to fine wool, the same amount of soaking will not produce an equally clean fleece. Fine fiber also tends to felt easier meaning it tolerates less handling. Fine fiber requires more work, but tolerates less handling. There is one brilliant tip that will help you scour fine wool effectively, and that is picking. 


A tip for ensuring the grease is released, especially when scouring fine wool is to add a picking in between two scours. 

Scour your fleece using your regular method. Let it dry completely. It may appear clean, but will likely still feel greasy to the touch. Take the time to pick the entire fleece either by hand (especially if it is super fine) or use a picker. Then, rewash the fleece for a second time (for fine wool use less soap to avoid the need for extra rinsing). Be extremely careful not to felt picked fiber by over-handling in the hot water. 

Evaluating Grease Content

The number one purpose for scouring wool that will be processed at a mill is to get the lanolin out. It is very difficult and maybe impossible to judge lanolin content in wet fiber. Knowing how to judge lanolin content could save you and your mill significant time later. Here are three ways to determine if your wash was effective. 

  1. Water Color - Before taking your wool out of the bath, try collecting a sample in a clear container. It is normal to have some color to the water, but any opaqueness is evidence of lanolin. Dissolved in water it has a milky white appearance. A good clean rinse water will be very much like a cup of white tea. 
  2. Smell - The smell of clean lanolin is pungent but not offensive. Many people find it a comforting, earthy smell which they attribute to the smell of wool. Familiarizing yourself with the distinct smell of lanolin is the only way to rely on it as a litmus. Once you can distinguish the smell separately from other wooly smells, the level of lanolin left in clean fiber should will be obvious with one big ol' sniff. 
  3. Touch - If the first two tests leave your ambiguous, try rubbing a few locks onto the palm of your hand. Does it feel greasy? Sticky? Or does it leave a shiny residue on your skin? If so, this is lanolin. The degree to which it is noticeable in any of these tests tells you what level of lanolin remains. Sometimes it is much more obvious than others. One last test you can do by touch is to hand spin a lock or two. Watch for that shiny appearance on your fingertips to build up over time. 


Scouring is by far the most expensive aspect of small batch processing because of how labor intensive it is. I have yet to meet a custom mill who isn't losing money on this step of the process. I'd LOVE to meet you if you're out there. At one point I even imagined what a portable scouring truck might look like? Could a traveling scour station add value to both small farms and mills? Elevating our collective, mutual understanding of effective scouring is certainly a good place to start. Please don't hesitate to share your questions and comments about this topic by email or in the comment section below. 


Think about your situation and choose methods that works best for you. Keep an open mind about learning something new each time you scour. Keeping a record of your questions and experiences with scouring will go a long way towards establishing an effective and efficient scouring routine.

Studio Reference is a category of posts containing technical insights and observations on working with fiber. The goal is to elevate our collective knowledge of textiles through an open dialogue about our questions, mistakes, lessons learned, and best practices with fiber. 

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