A question arose on Knitterguy's blog about a fleece that had some white stuff in it, and how the wool should be managed.
One of the topics raised in the discussion was scurf, which that particular white stuff wasn't. (It was probably lanolin, suint, and the like that had been dissolved and then redeposited on the wool because of temperature changes during washing; this happens most often with fine wools.)
However, there doesn't appear to be much information wandering around on the topic of scurf, which in the context of fiber processing is like dandruff, although most scurf I've seen comes in bigger flakes than dandruff.
Scurf is a nasty business to try to clean out of fiber. Here's what it looks like, being demonstrated by a lock of gorgeous, shiny, long mohair:

I say "try to clean out of fiber," not "to clean out of the fiber." The flakes are incredibly stubborn and difficult to boss around. They often hide inside the locks so you're not quite sure at first that they're there. The situation involves trying in all senses of the word.
Here's another photo, with the upper fibers of the lock pulled aside so the crud is easier to see:

Scurf is such a nuisance that it's a reason to pass up a fleece. I sure don't want it to get twisted into my yarn (because I think it's yucky), and it makes for bumpy spinning, too.
It may be worth working to banish the scurf if
it's in only a few places or you only need a small amount of fiber AND the fiber is beautiful and checks out okay in all other regards. That was the case with this fiber.
Scurf has irregular edges and even after the fiber (and the bits of skin) has been washed it seems slightly oily or greasy, so it tends not to fall out of the locks if you tease or card the fiber, like some types of vegetable matter (that may look similar) do. Those bits of vegetable matter are dry, which makes a huge difference. Carding scurfy fiber makes the problem worse because it breaks the flakes into smaller bits and scatters them throughout the fiber mass. (The same thing can happen to vegetable matter, but is more likely to occur during mechanical, rather than hand, processing.)
Sometimes combing (with wool combs of any style, English or Viking or mini) can remove the scurf flakes. But combs are expensive, most of them are not very portable (I work a lot when I'm places other than home), combing sometimes doesn't remove this type of crud, and I'm always looking for new ways to process fiber. In this case, I was changing locations frequently during the day. I also thought I'd lose a lot of fiber if I combed, so I didn't even consider it seriously. The scurfy bits were right in the middles of the locks—the middle both lengthwise and girth-wise. It's easier if they're at one end—they're usually at the cut end, nearest the skin, which makes sense. The formation of the scurf may have been precipitated by an illness or parasite problem. There's a reason I looked for mohair when I wanted a scurf example: while the problem occurs in sheep, it's more common in goats, so much so that I'm not surprised when I find it. I suspect that scurf occurs in healthy goats; someone more familiar with goat husbandry is welcome to let me know whether my suspicion is correct! This fiber certainly appeared to come from a very healthy animal.
With types of vegetable matter that are willing to fall out of the fiber when encouraged to do so, a dog comb can be very useful. It's worth trying here, too, even though scurf usually doesn't just fall out.

And the dog comb did do a decent job on this fiber. However, after about 10 minutes of combing on this lock (while waiting for the car to get its oil change), you can still see a bunch of scurfy
bits about a third of the way from the butt end (right side). The combing took WAY too much time and wasn't fun, and didn't do as thorough a job as I'd have liked (I would have taken a photo of the stuff that I did get out, but a big wind came up and blew it off the porch just before I snapped the shutter). The teeth of the comb tended to snag in the lock, so if I'd really gone at it I'd have pulled out (and wasted) a lot of good fiber.
On the way home from getting the car tended, I stopped at Poudre Feed & Supply and they encouraged me to take the dog and cat grooming tools out of their packages and try them. Most of the tools had teeth that were too soft and a few were too harsh. The guy who was helping me suggested that this might work:

(By the way, I appreciate places like Poudre Feed and Ace Hardware where I can actually tell the staff what I'm trying to find tools to do . . . whatever it is . . . and they don't look at me funny.)
Here's how that brush made relatively quick work of this scurf problem.
Holding the tip of a lock firmly, I drew just a bit of its cut end across the brush.

I worked progressively more deeply into the lock, while also letting it spread out across the brush. The fiber is moving, not the brush. I'm holding the brush steady.
I sometimes use my thumb on top of the lock to guide it deeply into the teeth (unlike regular carding where you want the fiber to stay close to the surface of the carding cloth). Although the teeth of this slicker are flexible and not too stiff, it's good to keep my thumb away from the tips as much as possible. A whole bunch of holding the thumb against the slicker teeth results in a thumb that looks (and feels) like it's been sanded.
The flakes move (slowly) down the lock as I continue to draw the lock across the teeth of the brush. Once the fibers start opening up, the flakes and just a few tangled bits of fiber begin to get caught in the teeth and stay there.
This is what I want. Flakes OUT of fiber. I could probably do this job the same way with one of my stiffest wool carders, but I don't want to have to clean the crud out from between the teeth or have it get into the next fiber I want to process with the carders. I also think this slicker brush was gentler on the fiber than the carder would have been.

The lock becomes broader and the fibers are spread more widely and the scurf gets caught in the teeth. The thinner the layer of fiber, the bigger the scurfy flakes are in comparison to the fiber. They can't hide as well and are more inclined to move down and out with repeated strokes across the brush.
Not much fiber is being snagged in the teeth, and that's good. I have to be careful to work all the way to the middle of the lock (because there's stuff there; in truth, there's stuff everywhere but the very tip of the lock), but to do so gradually so the fibers don't tangle and so I'm not having to work too hard.

Compared to the 10 minutes with the dog comb, we're now about 20 seconds into this lock.
I turn it around, hold the cut end, and begin to work gradually into the tip end.

After I've worked to the middle again, here's a nifty thing about this tool . . . I push a spring-loaded button on the back and the base pushes up and releases the crud from the teeth:

The brush is now clean for my next lock of the mohair, or anything else I want to work with. Getting the flakes OUT and AWAY from the fiber is primary here. Into the trash with them! As soon as possible!
Here's a lock before brushing. There's scurf hiding throughout that middle section. You can see just a little here and there. It's sneaky.

Here's a lock after brushing, with the debris and scurf (and tangled or short fibers) in a pad removed from the brush:

I could still work the middle a little better to loosen the fibers more evenly, but nearly all of the problems are gone. It took somewhere between 40 and 60 seconds, and wasn't aggravating.
When you think about using a minute per lock to clean the scurf out, you can see that you wouldn't want to do a whole sweater's worth nor would you want to invest the time in a mediocre fiber.
And you would think twice about taking responsibility for a very large batch of scurfy fiber, even if it was free.
Here's the yarn, just a sample, that I spun from about half a dozen brush-prepared locks:

It's perfectly fine yarn, but not perfect yarn, in part because of the legacy of the scurf. Here's a single strand:

Over on the lefthand edge there's a small jumble of fiber. I wasn't spinning a classic worsted yarn, but I was spinning to emphasize worsted qualities. That squidgy bit is a little snarl that formed when I tried to pick off yet another flake of scurf while I was spinning . . . against my better judgment, but in total concordance with my instincts. The yarn would have been smoother and more even if I had let the bit of scurf become part of the yarn, but I just couldn't. So I've got a small number of scrambled fibers instead, because I had to pry the flake loose.
Scurf. PG-13. Sometimes R.