We age soap to give the water content in it a chance to evaporate off, giving us a harder bar that doesn’t immediately turn to soap slime when it gets wet in our shower or soap dish. The longer you age a bar, the more water will evaporate, and the harder a bar will be. In really long-aged bars you’ll often notice the surface is a bit concave as the soap visually contracts from water loss.
As soap ages you’ll reach a point of diminishing returns. You’ll notice substantial differences in hardness over the first couple days of aging, but after a bar is a couple months or years old, those differences will be extremely subtle.
The typically suggested period of time for aging a bar of soap is three weeks, and this is what all of my soap recipes are based around unless otherwise noted on an individual recipe. However, aging time can be influenced by a couple big factors:
- The recipe. If your recipe uses a lot of soft/liquid oils, your soap will need a longer aging time (I’ve read 5 years for 100% olive oil soap). If your recipe uses a lot of hard oils (tallow, palm, lard), you may be able to age those bars for less time.
- The environment. If you live somewhere very dry your bars will obvious age much faster than if you live somewhere very humid.
Something else to keep in mind is that as soap ages, other things can change as well. If you used essential oils to scent your soap, those will fade. If you used botanicals to colour your soap, those can oxidize and change colour, or fade. If you age soap for a very long time it will shrink, and decrease in weight. Things that do not change through aging are lather or how gentle or harsh the soap may be on the skin—those things are determined by the recipe, and once saponification is done, you won’t see any significant changes through aging.
Posted in: Soap