Citric Acid in Cold Process Soap

Citric Acid is a great additive you can use in your soap. This article is about when and why you should use it and how to add it in cold process soap. If you prefer to watch this article instead of reading it, you can find the video here.

If you have very hard water you might know the problem of always having this white film in the sink. This is called soap scum. The main reason you might want to use citric acid is to get rid of this soap scum in your sink. Using Citric Acid in cold process soap is a great way to prevent that. If your water is very soft you might not have soap scum and therefore there is no need to use citric acid.

But how does citric acid in soap work?

When you make soap the citric acid reacts with the Sodium Hydroxide to Sodium Citrate.

Water, and especially hard water, contains minerals like calcium and magnesium. The harder the water the more minerals it has. Normal soap without citric acid will make soap scum from calcium and magnesium. When using soap which was made with Citric Acid, the Sodium Citrate in the soap then binds these minerals so they flush away and don’t sit in your sink. The Citric Acid so prevents soap scum.

But before you use Citric Acid for soap making you should have made some soap before and know about lye safety. This is nothing you should use as a beginner. If you need some help with Lye Safety, I wrote a guide to help you. You can find it here. So take your time, do some research on lye safety and first make some batches without citric acid. Using Sodium Hydroxide is an intense reaction, using additional Citric Acid is an even more intense reaction. So always be careful and know what you do.

Citric Acid is a white powder, looking like sugar, which you need to dissolve in water to use it. For this, you use some of the total water weight you would use for soap making. You don’t need extra water for this.

The normal usage rate of Citric Acid is 1 to 3% of the oil weight. When you make hair soap you can go up to 5%. Using more than that would not help.

You add the citric acid to some of the total water weight and let it dissolve completely. When using citric acid in your lye solution it gets hotter than normal. The citric acid will react with the Sodium Hydroxide and create Sodium Citrate. This reaction is very intense. Immediately there is a lot of heat and it looks as if it’s boiling. You will also notice a lot of fumes. And please, don’t breath in these fumes! So always be careful when adding the Sodium Hydroxide to the Citric Acid, take your time, add only small amounts at once and use ice cubes to keep it cool.

Because Citric Acid reacts with Sodium Hydroxide you end up having less Sodium Hydroxide left for the saponification and the super fat will increase. That means you will need to add some extra Sodium Hydroxide.

To calculate how much extra you need, you have to know that 10g of Citric Acid consume 5,71g of Sodium Hydroxide. Here is an example recipe:

To summarize everything:

• You only need to use citric acid when you have hard water
• Citric Acid consumes Sodium Hydroxide, so you need to add some extra Sodium Hydroxide
• The reaction between the citric acid and sodium hydroxide is very intense, so always take your time, add the sodium hydroxide slowly and use ice cubes to keep it as cool as possible