Almost two years have gone by since I originally set out to document our process of making soap from wood ash lye. I’m not always sure where the time goes and I often don’t have anything tangible to show for it. We burn wood as our only heating source in the living area of our house, so turning the buckets-full of ashes into something useful just makes sense. Previously I shared how we make wood ash lye water for soap making and stripping fur from animal hides and finally I have our soap making process picture documented. (that’s the hardest part, haha) Wood ash lye differs from store bought lye because it is Potassium Hydroxide. Store bought lye for soap making is almost always Sodium Hydroxide and the difference becomes apparent in the hardness of the bar it produces. That said, wood ash lye water that has been reduced enough and adulterated with a little salt can still produce a bar soap that is only mildly distinguishable from soap made with sodium hydroxide once it cures. We use tallow for our soap made with wood ash lye so that it starts off with as firm a base as possible, but there are drawbacks to that. Tallow does indeed make a harder bar of soap and ranks well on the conditioning scale, but it produces NO bubbles. To remedy this we add egg yolks so that it has at least a little bit of lather. I wish I could tell you to read on for a fail proof recipe where you follow steps A, B & C, like for most soap recipes but there are so many variables when making it with home produced ingredients that almost every batch has to be tweaked as I’m sure it also did back in the day. To make batches of soap like they did in old days really gives you an appreciation for the standardized versions of products that are available now. I’ll do my best to give you the tools you need to fine tune your soap, but even now sometimes we just wind up using whatever the soap turns out to be. Your soap has only two “active” ingredients so obviously those are the things that will impact your final product. Which type of wood your ashes are from and how concentrated/reduced you manage to get your lye water are really the basics of coercing potassium hydroxide to make a hard soap instead of a soft soap. Hardwoods such as oak and hickory make the best ashes for lye and tallow of any kind, beef, deer, bear, etc. will give you the firmest fat base. Adding salt and egg yolk then helps make up for the qualities the two main ingredients lack. Remember to think relative to the time period these were used and not expect a bar of current day type soap. In fact, what we buy in stores today doesn’t really resemble traditional soap at all. Most of it is made with petroleum based by-products and is technically a detergent… ie: chemically created. The same is loosely true with commercially produced lye. If you don’t really care if your soap is in bar form or “jar” form, you can skip the salt and have a wonderful soft soap that you can keep in a lidded pottery jar to be dipped out with your fingers.
As one of my “side hustles”, I make soap with sodium hydroxide, a variety of oils and milk from our dairy goats. I sell that “civilized” soap at the hardware store and at our local farmer’s market, so part of figuring out this recipe comes from that in depth understanding of how soap making works. When working with modern soap ingredients, measuring in grams as opposed to ounces is much more precise and once you have a small digital scale, I think it’s actually easier. There’s a lot of difference between ounce number one and how much it takes to tip the scale to the ounce number two. (I can’t believe I’m using the term precise in relation to wood ash lye soap…) But, precision is NOT as important when working with the ingredients we’ll be using for this soap. After all, no one had a gram oriented scale back in the day. Anyway, I still use a scale and have formatted the recipe in grams. I use an inexpensive scale like this one: Digital Scale. but any one will do, even one you can pick up at the post office for weighing packages. You can make the soap in either a crock pot or on the stove or outside over an open fire if you’re really dedicated to doing it the old way. The stove will give you a bigger range of heat adjustment than with the crock pot and will be quicker, but stove top cooking will make the soap darker.
Blah, blah, blah, lets get on with this. You will need wood ash lye and tallow.
If you don’t already have your wood ash lye prepared, you can find the directions for that here: Making Lye from Wood Ashes
If you have raw fat, you’ll need to render it and you can find directions for that here: Rendering Animal Fat
Wood Ash Lye “Bar” Soap
226 grams tallow
130 grams concentrated wood ash lye water
1 egg yolk (no white)
3 teaspoons regular table salt
Separate the egg yolk from the white and add the yolk to your measured tallow. Blend these two together while slowly melting the tallow over your chosen heat source. If you’re on the stove top, start low, somewhere around medium heat. High if you’re using a crockpot. A stick blender works well if you need to break up frozen tallow, but a spoon is all you need if you’re starting with it room temperature.
Next, slowly add the lye water, stirring constantly. Once the tallow, egg and lye are incorporated, add the salt. Stir continuously if you’re on the stove top and occasionally if you’re using the crockpot. Cooking will help the fats consume the lye (the process of saponification) and will cook off some of the water still being held in the lye. Depending on the water content in your lye and the amount of heat you use, this can take 20 to 40 minutes. That’s a big time span, but there are so very many variables. You can push the time if you’re on the stove top, but using the crockpot, you’re in it for more like an hour. If you’re not opposed to using a stick blender, the friction created by blender blades will cause saponification to happen quicker. Otherwise, the heat is the only thing spurring it along. The soap in the picture below needs to be stirred, but I wanted you to be able to see part of what happens while it cooks.
When your mixture is about the consistency of chilled pudding, place a dab on the corner of a plate so you can test it. Let it cool enough to touch then take a bit on your fingers and wash with it. You’ll be judging if you are left with a greasy feel or if it feels like suitable soap. If you find it greasy, slowly stir in a little more lye in 2-3 Tablespoon increments. (if you’re on the stove, completely remove the pot from the unit before adding more lye) Return to the heat and cook it down to chilled pudding stage again. Continue testing until it feels right. Keep track of how much you add in addition to the basic recipe above and next time you can start with that. If you’re consistently using the same type of wood ash for your lye, you’ll quickly have your measurements fine tuned to your type of ashes and lye strength. We want to have enough lye to make soap, but not so much lye that it become disproportionate to the fats. Is this making your head hurt, yet? 
Now consider the firmness of the dab you put on the plate. Does it cool to be firm enough? If not, add some more salt, or even baking soda. Soda will not have as pronounced an effect as salt, but mixes better after the soap reaches the chilled pudding stage. To throw another variable at you, whether your lye water was made with “soft” or “hard” water impacts how much salt you have to add at the end also. I wonder if the original homestead soap makers knew all these nuances or not. If you consider that what they might have learned living in one place may not have worked once they migrated to another place, it really gives an appreciation for what they were able to do.
Once you have the cleansing and firmness like you want, turn the soap out into a shallow mold and smooth down any clumpy spots. The mold can be anything from empty cardboard butter cartons cut in half lengthwise to one of the modern soap molds that are held together with screws. If you use something that cannot be torn off, like the butter carton, be sure to line your box with parchment paper so you’ll be able to get the soap out. Depending on the type of tallow you used, how browned it got as it was being rendered, and whether you’ve cooked on the stove or in the crock, your soap may be lighter or darker than the picture below. This also looks vastly prettier in the picture than it really is.
Let the soap cool overnight and then remove it from the mold. Even though this soap is technically ready to use because you’ve cooked it, if you let it “cure” a month or so, more of the moisture will evaporate and the bar will last longer. Equate this to how soap would’ve been made once a year at slaughter time (when they harvested the fat) and it makes sense that at least some of the soap would’ve sat around curing/hardening for up to a year. The longer it sits, the harder and better the bar. Also, the thinner you make the bar, the faster it will harden. I can attest to both of these facts.
Now. Soap like this does not smell good. I’ve tried adding essential oils and even the special soap fragrance but have not been satisfied with either one. Soap fragrance doesn’t behave well and makes the bar soft again. Essential oils do okay, but it takes too much and the smell never really masks the tallow and egg.
Also, if you’ve made regular soap before, be prepared that soap made with homemade lye is a much, much different process than what you’ll be used to. It goes through slightly similar stages as it saponifies, but still different. I’ve tried to cook it in a way to take it through all the stages typical to hot process soap from modern ingredients and it just doesn’t work that way.
One more note on this whole thing, when making soap this way, don’t be afraid to plug in your proportions to an online soap calculator or app. Most of them give you an option of either NaOH (sodium hydroxide) or KOH (potassium hydroxide). Choose KOH and 90% pure KOH if your calculator has that option. Our homemade KOH is unquestionably weaker than commercial KOH and using the 90% pure option is one way to help bridge the gap with calculated proportions. Let me know how your hard soap making goes, there are so many nuances that I’m sure I’ve forgotten something that could be added. If you have difficulties, chime in on the comments or send me a message and I’ll do my best to help you troubleshoot. 