What is dual superfatting?
Short answer
It's the book's signature technique: a standard superfat built into the lye calculation, plus a small amount of a precious oil added after trace.
Explanation
The primary superfat, around 6–7%, keeps the whole batch safe and mild. The secondary superfat, about 1–2.5% of the oils, is a special oil such as black seed, avocado, or a rosemary or rose macerate stirred in at trace. Oil added after trace is more likely to stay unsaponified, so more of its heat-sensitive botanical compounds survive in the finished bar.
What to do
- Add the post-trace oil first, then fragrance, then colorants.
- If you increase a post-trace oil significantly, recalculate the lye.
Source: The Big Book of Homemade Soap — Black Seed Luxury Soap: Harnessing Ancient Botanicals