Fat washing is an old perfumer’s technique of infusing something oily (such as bacon grease or bacon) into alcohol, then freezing the liquid so that the fat separates and rises to the surface so it can be scraped off. The flavor of the fatty substance remains in the liquid.
People often use this technique to get meat flavors (or sometimes just oil flavors such as butter or olive oil) into alcohol but meat carries the threat of botulism/bacteria poisoning. The alcohol alone will not preserve the fat-washed beverage. For safer fat-washing:
- Only a very small amount of the fats need to be used to properly infuse a spirit. Use the minimum amount needed to decrease the chance of rancidity.
- Make sure any meat used is fully cooked
- Any spoilable substance must not be exposed to air when infusing (don’t have meat sticking above the surface of the liquid)
- All fat-washing should be done in cold conditions such as a refrigerator
- Refrigerate or freeze all post-fat-washed liquids
- If transferring fat-washed liquids to another container, keep in mind that the meat or other spoilable substance could get stuck in the lines/cap, causing botulism/bacterial infection of other vessels. For example, never put fat-washed liquids on tap lines, and always wash caps of pour spouts at the end of a shift.
- The higher the ABV of the infused alcohol, the better.
- Use fat washed spirits within a few days.
One thing to keep in mind: If you wouldn't store raw meat there (on the counter, in an open-topped bottle, etc.) then don't store your fat washed product there.
What about oil-washing?
Some people have asked about the safety of fat washing just an oil, flavored oil, butter, and similar fatty but non-meat oils into alcohol.
While these are probably significantly safer, it is probably best to keep these oil-washed spirits in the refrigerator if not using within a couple days so that they don't go rancid - which is more a flavor impact than a safety one.
Further reading: "Has your food gone rancid?"