If you’re seeing a whitish or brownish coating on your leather and thinking, “Uh-oh, is that mold?”, take a breath! What you’re likely looking at is fatty spew – also known as spew or fat bloom. This is a natural occurrence where fatliquors used during the tanning process from within the leather migrate up to the surface, solidify upon contact with air, and create a waxy coating. And while it might look concerning, it’s easy to handle with the right steps!

What Causes Fatty Spew?

Fatty spew can arise from fats in the leather or oils used during tanning and rehydration. This sneaky wax can show up weeks after production and often occurs when items are packed in plastic in humid areas, “sweating” out these oils on long trips.

Quick Check Tip: Unsure if it’s fatty spew or mold? Just run a hair dryer over the area. If it melts and vanishes, it’s fatty spew. Mold, however, stays put.

How to Handle Light Fatty Spew

For light cases, take a hair dryer, apply gentle heat, and watch the fatty spew disappear as it melts. If it reappears, just repeat the process for a quick refresh.

Dealing with Moderate Fatty Spew on Water-Resistant Leather

For more noticeable spew that’s not easily handled by quick warming, here’s your go-to method:

1. Clean: Start with Geist Rapid Leather & Vinyl Cleaner. Spray a bit on a cloth, wipe down the surface, and let the cleaner get rid of any dirt and oils on top.

2. Degrease: Follow up with Geist Degreaser D1. This tackles the deep-set fats that make their way to the surface as fatty spew. Let it air dry, or use a hair dryer to speed things up.

3. Protect: Seal it all in with Geist Leather Preserver. While this won’t eliminate fatty spew forever, it gives the surface a protective shield and slows down future spew.

This quick routine is way more efficient than the constant blow-drying and wiping game – though keep in mind, humidity and temperature changes can encourage fatty spew to reappear over time.

When to Bring in the Pros

If the fatty spew keeps coming back, especially on porous or sensitive leathers, consider professional cleaning for a full solvent-based degreasing. And if you’re working with lots of leather goods (like bulk shipments), a professional approach can save you a lot of time and ensure your pieces stay spew-free.

The Science Behind Testing for Fatty Spew

Leather expert Gerber Andreas Ollert created a test for fatty spew:

1. Pour 50-100 ml of water into a 500 ml lab beaker.
2. Secure a piece of leather over the beaker’s opening, with the grain side up, using a rubber band.
3. Heat the water for 2+ minutes to let steam rise through the leather.
4. Remove the leather, dry the beaker, then re-wrap the leather airtight for 3-5 days at room temperature. No spew by the end? No long-term issue expected!