How to Prevent Orange Spots on Homemade Soap
Discovering small orange or brownish spots on bars that looked perfect at cutting is disheartening. Soapmakers often call them dreaded orange spots, or DOS. They are caused by oils oxidising and going rancid, and they are usually accompanied by a stale, crayon-like smell. While affected soap may still clean, spots spread and the smell worsens. Most cases can be prevented with fresh oils, careful formulation and good curing conditions.
What causes orange spots
Unsaturated oils, such as sunflower, grapeseed, canola and rice bran oil, are prone to oxidation when exposed to air, light, heat and moisture. When the unsaponified oils left in the bar oxidise, they create rancid spots and odours.
High superfat levels increase the amount of free oils in the soap, providing more material that can go rancid over time. Oils that were already old or improperly stored before soapmaking are a major contributor.
Use fresh oils and store them well
Buy oils from reliable suppliers, check best-before dates and smell oils before use. Rancid oils often smell sharp, fishy or like old crayons.
Store oils in cool, dark places in tightly sealed containers. Refrigerate highly unsaturated oils if you do not use them quickly, and avoid buying large quantities that will sit for months.
Formulate for stability
Limit oils high in linoleic and linolenic acids to modest percentages in your recipe. Stable oils like olive, coconut, palm alternatives, cocoa butter and shea butter create longer-lasting bars.
Keep superfat moderate, commonly around 5%. Very high superfat levels create softer, oilier bars more prone to rancidity.
Add antioxidants
Some soapmakers add rosemary oleoresin extract (ROE) or vitamin E to oils as an antioxidant to slow oxidation. Antioxidants work best when added to fresh oils rather than oils already beginning to oxidise.
Chelating agents such as sodium citrate or EDTA can help reduce oxidation caused by minerals in tap water. Distilled water is also recommended for soapmaking.
Cure and store soap properly
Cure soap in a cool, dry, well-ventilated area away from direct sunlight. Place bars on breathable racks, with space between them so air circulates.
Once cured, store bars in breathable packaging such as paper or cardboard boxes, away from heat and humidity. Avoid sealing uncured soap in plastic.
What to do with affected bars
Small spots can sometimes be planed or trimmed off, but if the smell is strong or spots cover much of the bar, the oils have deteriorated throughout. Many soapmakers keep such bars for personal use or discard them rather than selling or gifting them.
Record the recipe, oils, suppliers and storage conditions for batches that develop spots. Patterns often reveal a specific oil or storage issue.