What is superfat?

Explanation

The standard safety superfat is 3–10%, and most recipes in the book use 5–7%. Coconut oil is the exception. Because it's so saturated and stable, it can carry a 20% superfat for a skin bar without going rancid, while 0–3% makes a household or laundry bar. Oils high in unsaturated fats, such as olive or sweet almond, would go rancid at 20%.

What to do

• Set your superfat in the lye calculator; don't just add extra oil by eye.
• Use 5–7% for everyday bath bars, as the book does.