Homemaking · November 10 · 6 min read
What superfat means in soap
A little of the oil is never turned into soap, on purpose. You cannot see it as a layer.
Superfat is the portion of oil you leave unsaponified. You do it by using a little less lye than the oils could fully consume. That leftover oil stays in the bar as oil. It is why a well-made bar feels milder than a bar calculated to turn every drop of fat into soap. The tallow soap on this site is written at about 5 percent superfat. Five percent of those oils never become soap. The rest do.
What it is not
It is not a puddle you can see inside the bar. If oil is beading out of a cured bar and dripping, something went wrong, or the superfat was very high and the bar is soft. A normal 5 percent does not look like a spoon of oil sitting on a plate. The spoon in the photograph is only a way to show the idea. In the pot, that oil is mixed through the batter. In the cured bar, it is part of the bar.
It is also not the water. Using less water makes a harder bar that unmolds sooner. That is a water discount. The lye amount does not change. Superfat is a lye discount. People mix the two words up and then wonder why the bar is harsh or why it is soft.
How much is enough
Zero superfat can be a harsh bar, and it leaves no margin if the scale was a gram heavy on the lye. Five percent is the ordinary mild bar for a body. Push much past that, into the teens, and the bar stays soft, can sweat in a warm room, and can go off sooner because free oil is food for smell. A face bar and a laundry bar are not the same target. The laundry soap on this site is grated cured soap, not a high-superfat bar melted into the wash.
- About 5 percent: the usual body bar. This is what the tallow soap page uses.
- The number belongs to that oil list. Change an oil and the lye changes. The percentage is not a feeling.
- Oil rubbed on a finished bar is not superfat. Superfat was decided when the lye was weighed.
- A greasy, weeping bar is not a gentler bar. It is too much free oil, or it was not cured.
The lye essay explains why the finished bar can contain no free lye and still have been made with lye. Superfat is the other half of that sentence. A little oil was spared. The lye that was used was used up. Both can be true in the same bar.
