How to Make Homemade Lye Soap the Cold-Process Way

Learning to make lye soap the cold-process way is a rewarding experience. Not simply because you can brag to your friends that you have made homemade soap, but because you know that you’ve learned a practical skill; a skill that will benefit you even if you never make another bar of soap. It’s a basic skill that builds confidence and one that earns you a bit more freedom from “the powers that be”. It’s a step towards self-sufficiency and you know you’ll be better off if the $#!+ ever hits the fan.

As a friend and follower recently commented on our facebook page, “If things go ‘south’ in this country as some folks believe we are headed, you all will be the true survivors.”

Survival, independence, forging a connection with the past, or just plain fun – whatever the reason – making lye soap the cold-process way is a worthwhile endeavor. It’s an education in itself; a history lesson of an earlier time; a craft that should not be forgotten.



A pot of rendered deer tallow sat under the snack bar in our kitchen for at least a week or so as we gathered recipes and information on how to cold-process lye soap.


“Rendering is a process that converts waste animal tissue into stable, value-added materials. Rendering can refer to any processing of animal products into more useful materials, or more narrowly to the rendering of whole animal fatty tissue into purified fats like lard or tallow. …” source:


3 Important Things to Know Before You Start


  • weighing tallow is essential
  • a good soap-making recipe is important
  • and calculating how much lye should be used for the amount of tallow you have is necessary for success.


BrambleBerry has an excellent lye calculator that we recommend you use before starting your soap project.

After completing our research we purchased soap making supplies. We wanted completely separate soap making utensils so as not to worry about residual lye on any of our kitchen tools. To be thrifty, we purchased most of our supplies second-hand. You may have containers and utensils around the house that can easily be recycled for soap making. Lye (100% sodium hydroxide) was a bit more difficult to come by as grocery stores don’t always carry it in the drain cleaner isle, as in the past. We bought a container of lye at Ace Hardware.


A list of supplies for making lye soap:

  • 1 container of lye
  •  3 plastic containers – one for stirring the lye and water mixture, another for combining the tallow and lye mixture, and a third for a soap mold.
  •  2 wooden spoons (I’ve since heard that wooden spoons do not have longevity in cold-process soap making as wood deteriorates after continual contact with lye).
  •  a stainless steel pot (aluminum must not be used as the lye is caustic and will destroy an aluminum pan)
  •  a glass measuring cup for measuring the lye and water
  •  a thermometer for testing the temperature of the mixtures – both lye mixture and oil mixture should both be at 100 to 110 degrees before combining
  •  Latex gloves to protect the hands from the caustic lye which can cause serious burns –  we used Playtex Living Gloves
  •  an office scale that we had around the house to weigh the tallow
  •  safety glasses to protect eyes from accidental splashes from harsh chemicals


After weighing the tallow and calculating the lye requirements we were ready to begin the cold-process of making lye soap.



Work Outdoors if Possible

Soap making day was cold and sunny with temperatures around 23. We set up our soap making work-space outdoors so as not to worry about kitchen clean-up in case of lye spillage or other messes.


Lye Soap Supplies

Outdoor soap making work space. The white pieces are our rendered deer tallow.


After gathering our supplies, we took the following steps in making our lye soap:


  •  Measured the required amount of water for our recipe in the glass measuring cup. Poured the water into one of the plastic containers.


  • Measured the required amount of lye for our recipe in the glass measuring cup. Poured the lye into the container with the water . DO NOT pour the water into the lye as it will cause a quick chemical reaction that could be dangerous and splash.


Measuring lye for soap



  • Stirred the water and lye mixture to dissolve. The lye steamed less than expected and did not smell unpleasant as presumed.
  • Heated the deer tallow (it was stinky) on the stove in the stainless pot to bring outside for further processing. I think we should have started the melting process before mixing the lye and water as the tallow took a little longer to liquefy than anticipated.


Deer tallow in pot on stove ready for melting

Deer tallow in pot on stove ready for melting


  • Waited for both the lye mixture and tallow to each reach 110 degrees.


Testing temperature of tallow for soap



  • When the temperature was right, we took the pot outside and poured the oil into the empty plastic container. We then poured the lye mixture into the oil.


Pouring lye mixture into melted tallow for soap



  • We began stirring, and reached trace rather quickly, perhaps a false trace because of the cold temperatures (I had read it would be a lengthy process, up to 1/2 an hour if stirring by hand). Small globs of fat began forming. We stopped there and returned the mixture to the stainless pot and went back to the stove to melt the fat.

                       -Once melted, we returned outdoors where we stirred until trace.


“Emulsification is most easily identified visually when the soap exhibits some level of “trace”, which is the thickening of the mixture. (Modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how additives will affect trace, they may be added at light trace, medium trace, or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding. “Trace” corresponds roughly to viscosity.” source – Wikipedia


Stirring lye soap


  • Poured the liquid soap into the rectangular plastic container which was then covered with a towel and set aside to cure.



Pouring Lye Soap

(The mixture set-up rather quickly, reminiscent of making pralines. I wish the mixture would have settled a little smoother than it did.)

Lye Soap in Plastic Container


  • It was exciting to see that our soap had hardened and after 48 hours we were anxious to cut the soap which was pure white, but still had a slight tallow odor. We had left our soap making supplies a mess. In retrospect, I would have immediately cleaned them up with paper towels.


messy lye soap containers


Deciding to test the soap, I washed my hands with a small piece. It felt creamy, but shortly thereafter, I began to feel a burning sensation in my hands. I later read that by washing with homemade lye soap before it had fully cured, I was washing with raw soap. The lye and oils were still wrestling with one another, and had not fully homogenized. What that means is that that the burning I felt was due to lye.  Not as potent as before cold-process, but still too caustic for skin. I cannot over-emphasize how important the curing process is. Be patient. It’s okay to cut your soap after 48 hours, but wait for your soap to cure. It’s preferable to wait 4 to 6 weeks before using it.



In Conclusion

It’s been a week since we’ve made the soap and again I washed my hands with it. The tallow smell is gone and it didn’t irritate my skin. As a fine wine, the soap is improving with age, so I intend to wait for full cure before using it any further.


cold-process lye soap

Soap can now be shaped into nice bars.



Making lye soap the cold-process way was very gratifying. It gave additional purpose for harvesting Buck. I like that none of him is going to waste. Our next project will be to do something with his hide. We’ll see how that goes.

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