How to use Citric Acid in Soap Making

WHY USE CITRIC ACID IN HANDMADE SOAP RECIPES?

Citric acid is a useful ingredient in soap making. When dissolved into water and combined with sodium hydroxide (bar soap) or potassium hydroxide (liquid soap) to make a lye solution, citric acid becomes sodium citrate, which helps to reduce soap scum and reduces spoilage and DOS (dreaded orange spots) in finished soap products. (More weird soap making terms here).

Citric acid also helps to slow down the saponification reaction and results in a slower tracing soap batter, which is great for decorative designs and otherwise fast moving recipes.

Citric acid is especially useful:

• in hard water areas

• when making soap with old oils that might be going rancid or are beyond their expiry date

• when re-using salvaged cooking oil for soap recipes

• when making soap with intricate designs or where there is another reason to slow down trace

• when using oils that are high in linoleic and/or linolenic acid, which are more prone to rancidity and DOS (eg. sunflower oil, safflower oil, grapeseed oil, cottonseed oil, soybean oil, hemp seed oil, corn oil, sesame oil, wheat germ oil).
  
  *Check out this page and video about the different oils and fats (fatty acids) used for soap making

Below are the steps I use to calculate citric acid for my homemade soap recipes.

It is important to calculate your soap recipes carefully. Citric acid consumes a portion of the sodium hydroxide or potassium hydroxide amounts in a soap recipe, so compensatory adjustment is required.

*Please note that I am a hobby soap maker and am not formally trained in chemistry or skincare formulation. This method is my personal technique based on the results of personal research and learning from a range of other sources (see acknowledgements below).

HOW TO CALCULATE CITRIC ACID AMOUNT AND SODIUM/POTASSIUM HYDROXIDE ADJUSTMENTS

Step One

If you have identified that citric acid might be of benefit in your soap recipes, first calculate the amount you would like to use in your soap recipe.

I like to use 1-2% citric acid, by weight, of the total oil amount for my soap recipes (not including essential oils or fragrance, just the total of the main soaping oils). Using high amounts of citric acid is not recommended - it can leave small white crystals on the surface of the finished soap and can reduce cleaning performance.

Example calculation:

• My soap recipe uses 1000g of total base oils (not including essential oils or fragrance oil)

• I want to use 2% citric acid in my recipe

• My calculation is: 1000g x 2% (1000 x 0.02 in a calculator) = 20g citric acid

• Result: I need 20g of citric acid for my soap recipe

Step Two

The next step is to calculate the amount of extra sodium or potassium hydroxide needed for your recipe (remember that citric acid consumes a portion of these in the lye solution).

For sodium hydroxide soap (bar soap):

• Each 1 gram of citric acid consumes 0.624g of sodium hydroxide (NaOH)

• From recipe example above:

  • I want to use 20g citric acid (2% of soaping oils) in my bar soap recipe.

  • So, the calculation is: 20g x 0.624 = 12.48g of extra sodium hydroxide needed.

  • Add the extra sodium hydroxide amount needed to the previous amount given for the soap recipe. I round the new total amount down to the nearest whole gram of sodium hydroxide.

  • Record the adjusted sodium hydroxide amount in your soap recipe/notebook and note how much citric acid is being used.

For potassium hydroxide soap (liquid soap):

• Each 1 gram of citric acid consumes 0.842g of potassium hydroxide (KOH)

• An example for liquid soap:

  • Let’s say I want to use 1% citric acid for my liquid soap recipe, and I’m also using 1000g base oils.

  • The calculation for citric acid needed is: 1000g x 1% (1000 x 0.01 in a calculator) = 10g citric acid.

• Now to calculate the extra potassium hydroxide required…

  • So, I’m using 10g citric acid for my liquid soap recipe.

  • The calculation would then be: 10g x 0.842 = 8.42g of extra potassium hydroxide needed.

  • Add the extra potassium hydroxide amount needed to the previous amount given for the soap recipe. I round the new total amount down to the nearest whole gram of potassium hydroxide.

  • Record the adjusted potassium hydroxide amount in your soap recipe/notebook and note how much citric acid is being used.

HOW TO USE CITRIC ACID WHEN MAKING THE SOAP

The easiest way I have found to incorporate citric acid into my soap recipes is to dissolve the citric acid into the water reserved for the lye solution, before the sodium or potassium hydroxide are added.

For example, when preparing to mix a soap batch, I follow this procedure:

1. Put on gloves and protective eye goggles and ensure my soap making area is organised and well ventilated.

2. Weigh required citric acid into a small container or jar and place a lid on it (protect it from moisture in the atmosphere).

3. Weigh required sodium or potassium hydroxide into another container and close securely with a lid.

4. Weigh water amount for the soap recipe into a jug designated for making the lye solution.

5. When ready, remove cover and pour citric acid into the water, stir until dissolved.

6. When ready, carefully remove cover and gradually add sodium or potassium hydroxide to water-citric acid solution, stirring to dissolve.
   
   *NOTE: Citric acid in lye water solutions generate more heat and a more aggressive reaction when the sodium/potassium hydroxides are added. Be careful! Take your time, remove distractions before you start, protect your skin and eyes at all times and make soap in a well ventilated area.
   
   🛑 Please ensure you are aware of the full requirements for making soap safely > VIDEO HERE
   Soap making is fun and easy once you know what’s involved, but it’s still a serious craft! Never take yours or anyone else’s safety for granted, especially regarding the EYES! 👁👁

WHAT TYPE OF CITRIC ACID SHOULD I USE?

Food grade, anhydrous citric acid is the type required for soap making. This can be purchased from most supermarkets (in the baking aisle) or from soap making ingredients specialty suppliers. Here are some places you can purchase citric acid from in Australia.

WHICH Elly’s Everyday VIDEOS DEMONSTRATE OR DISCUSS THIS TECHNIQUE?

• Cold Process Soap Making ♡ Multi-batch session. Three interesting recipes to share.

• How to make soap using up bits of old oils! ♻ Recipe formulation and a fun surprise soap rebatch

• Pumice Stone Soap (smooth Solvol style)

SOURCES/FURTHER RESOURCES

• Classic Bells web page: ‘Citric acid and Citrus juice in soap’

• Kevin Dunn’s book ‘Scientific Soap Making’ (affiliate link)

• Jackie Thompson’s book ‘Liquid Soap Making’ (affiliate link)

  As an Amazon Associate I earn from qualifying purchases

OTHER USEFUL LINKS

• Calculate Soap Recipes to Fit Any Size Mould

• How to Calculate Your Own Soap Recipes

• Calculating Water in Soap Recipes and Clarifying 'Lye Concentration'

• Choosing Oils for Soap Making - Oil types and fatty acids, balancing recipes and Soapcalc explained 

• Superfat Explained - Understanding 'Superfat' and 'Lye Discounting' in Handmade Soap Making

• About Temperatures for Soap Making (cold and hot process methods)

• How to Calculate Simple Liquid Soap Recipes using the Zero-Low Superfat Method (with SoapCalc demo)

• How to make soap using up bits of old oils! ♻ Recipe formulation and a fun surprise soap rebatch

• About 'Gel-phase' in Cold Process Soap Making. What is it? Why consider it? How does it work?

• Handmade Soap Testing - How to test the pH of your handmade cold process or hot processed soap

• Soap Making Safety Essentials - Detailed Lye Safety Video - ESSENTIAL Viewing for ALL Soap Makers 

To comment:

1. Type your comment and click ‘post comment’

2. Enter your first name or an initial/symbol (any character will do the trick - it just needs to have something in the name field)

3. Click ‘comment as guest’ and your comment will be published.