Can you reheat lye water?

If you’ve made soap more than a few times and are human, you’ve probably been interrupted or had your soap making delayed. That hot lye water you were patiently waiting on to cool down has gotten too cold. Your melted soaping oils have started getting cloudy.

You may have to warm your oils up before you start making soap, but can you reheat the lye water? Should you reheat your lye water and is it going to cause problems?

You can safely reheat lye water when making soap, but you need to be careful. Heating it on the stove top can be dangerous and even microwaving it can cause problems. They trick is to heat it in a safe place and slowly. The best way to reheat lye solution is to use a hot water bath.

Let’s take a closer look at reheating your lye water, so you can prevent any bodily injury and still have your soap turn out fabulous.

Do You Even Need to Reheat Your Lye Water When Making Soap?

Before I go through the best way to reheat your lye water when making soap, let’s bust a few myths. You might be reheating it for no reason. Let me explain.

Myths About Lye Water Temperature in Soap Making

#1 – Your lye water needs to be warm or close to 110 degrees Fahrenheit. This is not always the case. Many soap makers successfully make soap at room temperature, or between 68 and 90 degrees Fahrenheit. It really depends on the oils in your recipe and how you need your soap to behave.

#2 – Your oils and lye water need to be within 10 degrees of each other. This appears to be an old wives’ tale in soap making. When I first learned how to make soap many years ago from a book, this seemed to be the golden rule.

I believe this came about when instructing new soap makers. If the lye and oils are close in temperature, it’s less likely you will get unpredictable results. For those who know the chemistry of soap making well, they understand the principles at work and what they can get away with.

Some soap makers even use their newly mixed HOT lye solution to melt the oils in their pot, knowing that the temperatures will average out in the end.

Now that we’ve busted those myths, you probably don’t even need to reheat your lye water and can save yourself that extra step!

How to Safely Reheat Your Lye Water for Soap Making

The safest way to warm up your lye water solution when you are making soap is to use the hot water bath method in a well-ventilated area where it’s safe from accidental spills.

Reheating Lye Water Step 1:

Fill a plastic bin or pot with HOT water. You don’t want to get it too hot. I would start with 135 to 140 degrees Fahrenheit.

Your water bin or pot should be large enough to fit your lye water container with 2-3 inches extra on each side. Don’t overfill it. You want the water to be close to the same level as your lye solution level in the pitcher, or you lye may go all floaty-floaty on you, tip over and spill.

Reheating Lye Water Step 2:

Place your hot water bin in a safe area away from kids, pets, spouses, etc. You don’t want it to get bumped and spilled.

I suggest a sink. That way, if it does spill you’ll have a much easier time cleaning things up and are less likely to get any burns.

Reheating Lye Water Step 3:

Place your lye solution container in your hot water bath and stir it often. Maybe every minute or two. You’ll want to keep a close eye on the temperature, otherwise it may get hotter than you want it.

Also be aware that reheating lye can cause the fumes to start up again. Those fumes are not good to breathe, so treat this process as carefully as you do when you mix your lye in the beginning.

Reheating Lye Water Step 4:

Once your lye solution is up to the temperature you want, carefully remove it from the bath, and wipe the excess water from the bottom. You can then put in in a safe place until you are ready to pour it into your oils.

WARNING: It can be dangerous to heat lye water on your stove top or in your microwave. The stove heats it much faster and the microwave unevenly, giving you less control. This means you are more likely to overheat it, and have more fumes released.

When microwaving, you run the risk of getting a face full of fumes when you open the door. If microwaving is your only choice, do it very slowly (no more than 10 seconds at a time).

I really don’t recommend microwaving it, especially if your microwave is above your stove or higher up. It’s just more dangerous to be working with it above your head.

When to Reheat Your Lye Water an When You Shouldn’t

Again, the good news is you usually don’t need to reheat your lye water if it cools down more than you expected. You may even WANT IT COLDER than normal for your benefit! Let’s take a look at when you want cooler lye water vs. having warmer lye water and what it does in soap making.

When to Use a Cooler Lye Solution Mix in Soap Making

There are definitely times when working on a soap recipe that you actually want and need your lye solution to be cooler.

You want to slow down trace.

Your lye water and oils both need to be on the cooler side for this, since heat speeds up trace. This is where you “soap at room temperature” with your oils and lye solution sitting around 80 degrees Fahrenheit. When you slow down trace and the speed your soap batter thickens, you have more time for swirls and fancy-pants designs.

You’re adding milk to your soap.

Milks, like goat milk and milk kefir, tend to scorch easy with extra heat. If they scorch, they turn a darker brown. (It’s still fine to use, but may not be what you are aiming for.)

The cooler your soap is when you mix it means it won’t reach as high of temperatures as it turns into soap. Some soap makers even like to put their soap in the fridge for 24-48 hours while it saponifies to keep it from getting too hot.

Start cool, stay cool!

Directions on how to make scorch-free milk kefir soap are right here.

Beer or sugar are part of your soap recipe

Any type of sugar, including beer, honey, organic table sugar, etc. will create a chemical reaction in your soap that produces extra heat. The more sugar you are adding, the more heat you will get.

When adding sugar, it’s beneficial to use a room temperature lye solution. That way you can prevent a soap volcano in your soap mold, while still enjoying the humectant benefits of honey and the extra bubbles from sugar.

When to Use a Warmer Lye Solution Mix in Soap Making

Just like there are times you want your lye water on the cool side, there are instances where warm lye solution is a must!

You want to gel your soap.

Your soap has to get a little bit hotter to go through gel phase. You can do this by putting your freshly poured soap onto a heating pad, or putting it in a warm oven.

Either way, the warmer your soap batter from the beginning, the easier it is to get your soap to gel all the way through. Warmer lye water and oils make this easier. It also helps to prevent soda ash from forming.

If you’re looking for the secret to preventing soda ash on your soap, click here!

You’re making a castile or bastille soap.

Castile soap uses 100% olive oil and bastille uses mostly olive oil in the recipe. Olive oil is notoriously SLOW to achieve trace, so you can imagine how much stirring and/or stick blending you’ll be doing if that’s what you are making.

You may want to increase the temperature of both your oils and lye water when making castile and bastille soap. It’s simply to cut WAAAAY down on how much stirring and stick blending you will have to do. Save your arm and your stick blender the extra wear and tear by soaping warmer.

Helps to prevent a false trace.

False trace happens when the harder fats and butters in your recipe start to cool down enough to solidify. When mixing, this solidification can appear to be trace, especially to newer soap makers.

When your lye is cool, especially cooler than the melting point of your fats, it can firm them up making them look like they are in trace. If your soap is only at a false trace, you may pour it too soon and have it separate in the mold.

This usually isn’t a problem if your recipe has fats and butters that have lower melting points, or if your recipe has a small amount of the high melting point oils. The exception is beeswax. Even in small amounts you will want to be careful.

Here’s a handy chart with the MELTING TEMPERATURE of common solid fats & butters:

FAT/OIL/BUTTERAPPROX. MELTING POINT
(In degrees Fahrenheit)
Tallow108-113
Beeswax144-147
Cocoa Butter100
Shea Butter90
Stearic Acid131-158
Palm Oil105
Palm Butter119-135
Palm Kernel Flakes102
Coffee Butter104
Kokum Butter97-104
Approximate melting point for common fats, oils and butters in soap making.

Cooling Your Lye Water When It’s Too Hot

OK, so you’ve successfully heated up your lye water… too much! Now what? You do the same thing you did before, only you use a cold water bath in a bin in your sink. Or, you can simply let it cool down again naturally.

Pro Tip: If you have to put your soap making project on hold, AGAIN, then you can store your lye at room temperature for up to a week and it will still work to make soap. Just make sure to clearly label it, put on a tight-fitting lid and keep it locked out of the way. You don’t want a family member to accidentally spill it!

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