Low-Cost Survival Hygiene: Making Lye Soap From Fat and Wood Ashes


We’ve previously taken a look at wood ashes, and as promised in this article we’re going to delve into one of their most prominent uses as a soap-making ingredient. Lye soap is actually quite old, having been used by many different cultures and societies around the world as a way of profitably reusing meat drippings and the remains of old campfires. For the preparedness minded, lye soap is a convenient cleanser for the body and many other surfaces in addition to being an easily transportable barter item.

Disclaimer and Important Safety Info. I put disclaimers on most of my posts, but in this case you should really take a moment to read this. Lye in its distilled form is extremely caustic, and it can easily eat through your skin, muscles, fat, and even the nerves without you noticing until it is much too late. Always cover exposed skin, wear eye goggles, and wear thick rubber gloves when making lye or handling it when making soap. Always use lye in a well-ventilated area. Be extremely cautious with it and you should be fine.

Furthermore, despite what you may have heard, vinegar is an absolutely terrible idea when you are burned with lye, as the reaction between small amounts of vinegar and burning lye will actually cause extreme heat, which will add a thermal burn on top of the chemical one. Rather than trying to neutralize the lye with vinegar, simply dilute the lye with as much water as you can by vigorously rinsing it and rinsing it as much as possible. I would recommend that you have someone else (such as a helper!) call 911 so you can focus on washing the lye until they tell you different. This website goes into the nitty-gritty of why this is, so please check it out if you aren’t fully convinced.

With that little disclaimer out of the way, let’s delve into the soap-making!

First step, getting the lye

The first thing you need to make lye soap is, naturally, the lye. This is typically derived from wood ashes, specifically ashes from hardwood trees as they tend to be less resinous and give better product over all. The method for taking ashes from your fire and turning them into lye is as follows:

Lovely brown lye water. Make sure you don't use a metal container!

Lovely brown lye water. Make sure you don’t use a metal container!

  1. Gather the fine white ashes (not wood chips if any remain) and place them in a container that can resist the alkalinity of the lye. Metal and glass are not suitable for this task: use plastic or wood. This container should be large enough to hold several gallons of water, and ideally should have a tightly closable lid to avoid accidental spills or splashings.
  2. Gather several gallons of soft water, usually rainwater works best. Water from wells and rivers tends to be filled with additives that interfere with soap-making, and you may need to add a few scoops of baking soda to the water if you don’t have sufficient rainwater handy.
  3. Slowly and gently pour the soft water over the ashes, taking care to avoid splashing. Stop when you start seeing ashes floating around in the water instead of dissolving.
  4. Allow the mixture to sit for at least 24 hours, though it may be even longer. The water needs time to leach the lye out of the ashes, and you’ll know there’s lye in the water once it starts turning brown.
  5. Test the water periodically by adding an egg or potato and seeing if it floats in the liquid. If it floats with about half of the egg or potato showing, your have the proper ratio of lye to water. If it sinks too much, you have too much water and you need more ashes. If it floats higher, add more soft water since the lye concentration is too high. Alternatively, place a single bird feather in the mixture and see if it dissolves the feather to determine proper concentration. Immediately dispose of any foodstuffs that touch the lye water, and do not put it in a compost heap.
  6. Carefully scoop out the lye from the surface of the water into another resistant container for final boiling. You’ll want to use avoid getting actual ashes on your skimming tool of choice, but otherwise just avoid splashing.
  7. Test the lye again for proper balance.

Preparing the fat

Fat is the other primary ingredient in lye soap, whether it be leftover fat from butchering or just the drippings of grease from cooked meat. Fortunately this is a lot easier and safer to deal with than the lye, though you should watch for grease fires.

Once the fat has been cleaned and hardened, scrape off the muddy looking junk and use the pure white fat.

Once the fat has been cleaned and hardened, scrape off the muddy looking junk and use the pure white fat.

  1. To clean the fat, pour the liquid drippings through multiple layers of cheesecloth in order to strain out gristle and meat bits from the fat.
  2. Bring equal parts grease and water to a boil, then remove the mixture from the heat source and add another 1/4 of water.
  3. Once the fat has solidified, remove anything that looks “dirty”, leaving the clean fat behind. Continue this cycle until the fat is pure.
  4. On your final cleansing add about a spoonful of salt to the mixture. If using drippings of fat from cooking, also boil this last load in a mixture of 1/2 cup of water mixed with a few spoonfuls of vinegar per cup of fat you’ve collected.

Bringing it all together to make soap

Now you need to mix the fat and lye together to make your soap. The goal is to use the fat to solidify the mixture while the lye works to keep the greasiness of the fat to a minimum, making a nice liquid mixture that can harden into a bar of soap. Generally speaking the mixture should be 12 parts lye to one part fat. Take care to properly dilute the lye during this process or the soap will remain caustic and dangerous to the skin!

  1. Mix lye in about 10 quarts of water and begin boiling it. This gets the lye ready to be mixed in with the fat and dilutes it a little more.
  2. Mix in your fat, maintaining the boil. You don’t need to stir just yet, but you do want the fat to desolidify if you let it harden back up between the first cleaning and when you decide to make soap.
  3. Add 4 more quarts of water and begin stirring the mixture together as it boils down. Continue mixing until it is about the consistency of corn syrup, dripping but solid.
  4. Place a little bit of the mixure in a mold and let it dry into a bar of soap, then test it for proper feel and lye concentration. If it burns, add more fat to the rest of the mixture with water to dilute the lye. If the mixture is very greasy and the mixture has lots of scum on top of it during stirring, add more lye to break it down. Err on the side of too fatty rather than too caustic, since fat isn’t likely to hurt you!
  5. Once you have tested and found the proper balance, make as many bars as you wish and enjoy scrubbing. The soap is great for people as well as general household use. Flakes can even be shaved off and added to laundry washwater for homemade dish soap.
Lye soap can be quite soft, and is a great homemade item for preparedness.

Lye soap can be quite soft, and is a great homemade item for preparedness.


And that’s all you need to make your own lye soap at home. Be careful with the lye and balance the concentration correctly and you should avoid any burns and have a safe, fun time making this stuff.

Your thoughts?

Do you have anything you would add to the soap? Have you made your own before? Give us any advice you may have in the comments below!


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  1. Have you actually used this method? 12 to 1 ratio of lye to fat? That isn’t much fat. And there is no need to “clean” the fat, just render it; a slow cooker works great for this. Also with water in the rendering step, water in the lye step, and more water added in the soap making step, it sounds like a lot of water in the recipe. can’t imagine it would ever harden up. And you don’t let the soap age before use?

  2. mercy huss says:

    I have made goats milk soap for years, and have to say that at least for small splashes of lye which I feel as sudden burning on my skin, I have always applied white vinegar and it has worked very well to immediately stop the burning sensation and prevent any burns. Maybe what they are warning about are large amounts of lye…

  3. TheSurvivalGuy says:

    Great article as always. We use a wood stove to heat our home I am going to try this out. Question?? We use newspapers to start our fires, will this cause any problems in gathering the lye or its’ quality?

  4. Renee Williams says:

    As a professional (small business) soap maker, I’m curious as to where you get your ratios of Water to Lye, Lye Solution to Fats, Drying/Cutting Times (which I didn’t see mentioned at all) Curing Times (primarily intended to allow excess water to evaporate from bars so that they harden up better and therefore last longer) and Whether you’ve ever worked with a standardized recipe that actually uses known SAP values for the specific fats you’re using (beef vs chicken vs deer vs pork vs nut oils vs plant waxes or beeswax) and what proportions you’re mixing those in.

    I’m also curious as to your reasoning in leaving your fats in their solid state and boiling the mixture after it’s introduced to the lye solution – essentially forcing a Hot Process – rather than melting your fats, monitoring the temps, and mixing them OFF the heat in a Cold Process. While Hot Process does frequently speed things up a bit, it can also be tricky for those who are unfamiliar with soap making, and requires considerably more “babysitting” than cold process soaping does. Hot Process is Also more generally used as an industry standard when formulating Liquid soaps that are never Intended to be solid/bar soaps, using KOH (potassium hydroxide) rather than NaOH (sodium hydroxide.)

    Keep in mind, Soap in and of itself IS the end product. There IS an actual KNOWN science involved in the saponification process. The fats and lye react together chemically to break down and form a salt precipitate byproduct – that product being your soap. The fats do not “solidify the mixture.” The chemical salt precipitate of the Acid/Base solution (fats are acids, and it is the specific varied acids IN the fats which react with the lye to give your soap it’s various qualities) Is a solid in nature, and falls out of solution with the water, which then slowly evaporates off. Your ratios of Fat to Lye should be specific enough that all Lye is consumed in the saponification process, and there is approximately a 1% (for clothes/dishes/etc) to 6% (for body/hair use) Superfatting component. There is even Science involved in what makes a good Bar soap vs what makes a good Liquid soap. It’s a matter of Long Chain vs Short Chain precipitate formed when the acids and alkali mix – the long chain formation of using NaOH tends to snap when placed in solution with Water, where the much shorter chain formation caused by KOH doesn’t, and therefore retains it’s “slippery” feel even while held in solution.

    That’s why there are a Plethora of Good Sites out there on the web these days with SAP tables, and even free to use SAP calculators, and a few of them even have the specific Math Formulas listed so that if you know the SAP value of a given fat, you can do the math yourself via longhand or calculator rather than using an online computer calculator program. I’ve used a program for several Years now that is free to download one version of – which includes known SAP values for a LOT of different commonly used fats, allows customization of recipes, tells you what your Lye to Fat ratios should be based either on your Weights or on the Percentages you wish to use of specific fats, allows you to include Additives like Honey or Glycerin (another Natural byproduct of the Soaping Process) or coloring agents (I use a Lot of super finely ground herbs, and there are even websites that will tell you which herbs will produce which colors and how to obtain those colors!) or scent.

    I applaud your safety/disclaimer – Lye CAN be dangerous to work with if you’re sloppy or careless, and it IS best to wear safety goggles and Thick non-reactive rubber gloves. I question your comment about not using Glass containers to mix your Lye solution though. I’ve used both Glass and Plastic containers for mixing Lye up to a 40% solution (though I generally don’t use higher than about a 30%) – neither will react, and well constructed glass containers are often much more Heat Resistant than plastics or woods. Lye (NaOH) as it reacts with Water (H2O) is Exothermic and produces it’s own heat source. This is part of why Cold Process soap making doesn’t Require an outside heat source when mixing lye solution or the lye to your rendered, melted fats. The only heating necessary is TO melt your solid fats into a liquid form for mixing with the lye solution.

    • Wikipedia says use the wooden barrel or glass. I’ve seen youtuber’s using. Stainless, castiron, plastics and wood barrels. All Ma Ingal’s had to use was a cast iron pot! Could you please email me that software link..Thanks. Check out the YouTube: by Mist Prepper making soap at Martha’s.

  5. I have seen this done with drippings and woodashes but it was much more simple. take ur drippings, render it, scoop of the top. Then slowly pour water through hard wood ashes using a handkercheif as a strainer to make lye and then do 2 parts glycerin to 1 part lye. Way easier. Instead of flaking for laundry soap just add it to your wash tub before it solidifies.

  6. I also had wondered about putting it in when liquid thanks for your input Jake.

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