Why are there orange spots on your soap?

Oils to avoid or reduce to limit orange spots and rancidity

You have just made a gorgeous natural soap. You gently place it on its shelf to let it dry... and a few weeks or months later, small orange spots appear on your soap. At first, you think you messed something up. But you only need to get close to the soap and smell that slightly rancid scent that tickles the back of your nose to understand the obvious. Some oils have turned, but the mystery is a bit more subtle than a simple failure.

These spots, known on forums as Orange Spots, are simply a sign of fat oxidation. Of course, some oils are more sensitive to this than others. But rest assured, that doesn’t mean you need to banish them from your recipes. It just means learning to use them with a little extra caution.

Why can an oil go rancid?

Not all oils react the same way to oxygen. Some contain higher amounts of polyunsaturated fatty acids, which are more sensitive to oxidation. Heat, light, and exposure to air can accelerate this process. Therefore, a soap rich in sunflower oil kept in a closed, hot, tropical climate will tend to go rancid much faster.

And even though part of the oils turns into soap during saponification, the remaining fats and certain components of the formula can still be sensitive to oxidation. That is why two recipes that look very similar on paper can have different shelf lives.

Oils rich in polyunsaturated fatty acids

When you want to formulate a soap that keeps well, oils very rich in polyunsaturated fatty acids deserve special attention. This doesn’t mean they are bad for soapmaking. On the contrary, some are very interesting for their properties and can bring a huge amount of benefits to the formula. The problem mostly comes from their proportion and their freshness.

Hemp oil

Hemp oil is very interesting in formulation, but it is also relatively fragile. It can bring a nice variety to a recipe, but its fatty acid profile makes it more sensitive to oxidation than more stable oils. A small amount can therefore be easier to manage than a very large proportion. And as with all fragile oils, freshness and storage matter immensely.

Walnut oil

Walnut oil is also part of the oils rich in polyunsaturated fatty acids. It can be used in soapmaking, but it is best not to treat it as a particularly stable base oil. If you have had a bottle of it in your kitchen for several months and are wondering if it is still suitable for your recipe... check its odor before using it, because it might no longer be good for your formula.

A fragile oil is not necessarily a forbidden oil

When you start reading information about soap rancidity, you can quickly get the impression that there is a list of "forbidden" oils. It is not that simple. A fragile oil can have its place in a recipe. The idea is rather to think about the general balance of the formula.

A recipe composed mainly of relatively stable oils and containing a small amount of a more fragile oil does not have the exact same profile as a recipe where the majority of oils are very sensitive to oxidation. It is therefore often a question of proportion.

On the other hand, beware of your old oils

We talk a lot about the characteristics of different oils, but there is another element: the age of the oil. A fresh, properly stored oil is not the same thing as an oil that has spent months open near a window or next to a warm object.

Before using an oil in a soap, get into the habit of checking:

• its date

• how long it has been open

• its smell

• its appearance and color

• and how you stored it

If an oil already smells distinctly rancid in the bottle, it is better not to count on it.

What if orange spots appear anyway?

Don't panic. Orange spots do not mean that the whole recipe was bad. Instead, try to figure out what might have promoted the oxidation.

• What was the composition of the recipe?

• Were the oils fresh?

• How had they been stored?

• Was the soap exposed to a lot of heat or humidity?

• Did the recipe contain a significant proportion of fragile oils?

By writing down this information with every batch, you will gradually be able to spot trends. That is also why a formulation notebook is so useful in soapmaking.