The Suint Fermentation Method (SFM) – an experiment

The Suint Fermentation Method (SFM) – an experiment

After stumbling upon a blog discussing SFM, I was intrigued and dove into YouTube videos to learn more. Through my research, I discovered that SFM offers a remarkably simple, water-efficient, and chemical-free way to clean raw fleece at home, making it an attractive alternative to traditional methods that consume large amounts of water and chemicals. As someone interested in sustainable practices, I was eager to experiment with SFM and explore its potential benefits.

What actually is Suint Fermentation?

This method can be used to clean any fleece, regardless of how dirty the fleece is, in fact, the dirtier the fleece the better! Sheep’s wool naturally contains a substance called suint, which is a mixture of sweat, minerals, and potassium chloride (potash). When sheep graze, they absorb potash into their bodies, which combines with their sweat to form suint. This substance builds up on their wool and can make up a significant portion of the wool’s weight, especially in finer breeds like Merino sheep.

When using the SFM, you’re harnessing the suint which is a natural soap-like substance that will help clean the fleece by breaking down dirt and impurities. To further aid in cleaning, the fleece is left to soak for a period, allowing anaerobic bacteria (bacteria that thrive in low-oxygen environments) to break down tough dirt and debris, like chunks of manure. These bacteria feed on the impurities and help clean the wool. Once the fleece is removed from the water and exposed to oxygen, the anaerobic bacteria die, eliminating any unpleasant odours. SFM leverages the natural properties of suint and bacteria to efficiently clean the wool.

Giving SFM a go

I recently purchased raw Gotland locks from Tawhai Gotland for an upcoming felting project and was excited to try the SFM. Although it’s recommended to do SFM in warmer weather, as the bacteria that break down the suint and impurities thrive in temperatures above 20°C, I decided to give it a try in my greenhouse, where even in May, temperatures exceeded 40°C on fine days. The warmth would likely still support the bacteria growth and fermentation process, and I was curious to see if it would be effective even in autumn.

I scrubbed out a bucket with a lid – crucial for creating an anaerobic environment that fosters the growth of beneficial bacteria – added the locks, and covered them with rainwater. Rainwater is essential for SFM because it’s soft water, which allows the suint and lanolin to dissolve more easily. Hard water, on the other hand, contains mineral deposits that can interfere with the fermentation process and reduce its effectiveness. After placing the bucket in the greenhouse, I waited for a week, during which the anaerobic bacteria did their magic. When I lifted the lid, the murky water and film on top indicated that the process was working. Although I expected a strong sulphuric smell, it wasn’t as pungent as I’d anticipated.

During the second week, the greenhouse temperatures remained warm, providing ideal conditions for the bacteria to continue breaking down the suint and impurities. When I lifted the lid after week two, the smell had become more pronounced, although I suspect it would have been significantly stronger if I had started with a heavily soiled fleece. The water had become even murkier than before, and the film on top had thickened, indicating the ongoing fermentation process.

After tipping out the murky water, I rinsed the locks thoroughly, and it didn’t take long for the water to run clear, washing away the grimy film. If I had other fleeces to ferment, I would have saved the murky water as a “starter” culture, which would introduce the established bacteria to the new fleece and accelerate the fermentation process. This technique can reportedly reduce the processing time to just a few days, provided the conditions are optimal.

When rinsing the fleece, it’s crucial to handle the wet wool gently to avoid felting, as it can easily mat and tangle. I set up an old clothes horse in the greenhouse and carefully laid out the locks to drip dry. It’s worth noting that the SFM process doesn’t break down vegetable matter (VM), so any VM present will still need to be removed after the wool is dry. Fortunately, the locks I used had minimal VM.

Although the smell persists after rinsing, it completely disappears once the wool is dry, as the bacteria die off. The dry wool retains its quality even when rewetted, without the smell returning. I’m thrilled with the outcome – the locks are exceptionally soft, with a subtle, neutral sheep scent that’s barely noticeable. They’ve retained their structure, making them perfect for my felting project.

Final thoughts

There is no specific water-to-wool ratio required for SFM, just ensure the wool is fully submerged. The fermentation time will depend on the fleece’s condition, with longer periods resulting in cleaner wool. For my relatively clean locks, two weeks was sufficient, but heavily soiled fleeces may require a month or more. However, using a starter culture can significantly speed up the process. Notably, the fermentation time remains the same regardless of the fleece size.

Whether you have a greenhouse to facilitate year-round processing or prefer to wait for spring’s warmth, SFM is worth trying for its gentle and chemical-free approach to cleaning raw fleeces!

Written by Daniel Godfrey 2025