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What is a Seize in Soap Making?


Lady screaming about soap

What to do?!? My soap is a mess!

John Richardson/ Getty Images
Everything is going along fine.

You've carefully poured your lye solution into your oils and have begun to stick blend it.

You've reached a light trace and poured your fragrance oil in.

(Cue the ominous music.) Bam! Suddenly your lovely smooth lightly traced soap becomes a thick mass of mashed potatoes or cookie dough-like glop. You can hardly stir it, let alone blend it smoothly. What happened???

You've experienced seize. The chemical reaction (saponification) between the lye and the oils has fast forwarded/overreacted itself into a big, thick mess. There are light seizes, where things just get thick quickly and you have to work fast...and there are super seizes where it goes from liquid to glob in a matter of seconds.

If this has happened to you (and it's happened to most all of us at one time or another), you probably have two questions:

  1. What caused this?
  2. What can I do now?
What causes seize in soap making?
There are a few alleged causes of seize. The most common suspects are fragrance oils. Some fragrance oils, because of one of the constituents/compounds will speed up the trace and/or cause seize. Floral fragrance oils are the most commonly reported to cause seize - fragrances like lilac or lily or gardenia. Some essential oils, especially spice-type essential oils like clove or cinnamon, can cause seize, too. Other culprits include alcohol - for example when using wine or beer as your soap making liquid, or again, just in the fragrance oil. I have heard people say that a high percentage of castor oil, jojoba oil or beeswax in the recipe can contribute to seize, but I've not ever encountered this.

What can you do now?
First and foremost, try to prevent it. Buy your fragrance oils from reputable vendors. Many will tell you on their websites if a fragrance is "prone to cause acceleration." (That's the nice way of saying "watch out for seizing.") If you have a fragrance oil that is prone to seizing, there are some things you can do to minimize it:

  • Be sure to keep your temperatures on the low side. Keep your lye and oils in the 90 degree range, rather than the 100 degree range. This helps slow the saponification down.
  • Dilute the fragrance oil in some warmed oils. Take several ounces (about 4X the amount of the fragrance oil) of warmed oils out of your soap pot before you put the lye in. Mix the fragrance oil into the warmed oils. Then, when it's time to add the fragrance at very light trace, add the oil-fragrance mixture. The warming and the diluting seems to help minimize the shock factor when the fragrance is added to the pot.
  • Don't discount your water very much, if at all. I usually recommend 2X the lye amount as the water amount. (If your recipe calls for 4 oz. of lye, use 8 oz. of water.) With seize-prone fragrances, up that to 2.5X or even 3X. The extra water helps slow things down considerably.
  • Be prepared. If you know this recipe/fragrance is going to get to trace quickly, don't plan elaborate swirls or colors or additives. Just have everything ready to go - and go quickly and efficiently.
When all else fails
Let's say this is your first major seize, or you've done everything above, and your soap still turns out as a glob of dough in your pot. Don't panic. There are a few things you can do to save the batch:
  • Just scoop it out and mash it into the mold(s). If you're fairly sure that you've blended everything into the soap relatively well before it seized, just scoop it out of the pot and mash it into the mold. It's not going to be smooth, pretty soap; you're not going to get details on single-cavity molds, but it will be fine otherwise.
  • Wait for it to gel. (Only use this technique if you're very comfortable with your understanding of the soap making process and know exactly what "gel" stage looks like.) The saponification process has started in the pot, and if it's sped up this quickly, you're likely to get a nice hot gel stage. When the soap is in gel stage, it will be much softer and more pliable, so you'll be able to scoop and mold it easier. Insulate your pot well with towels on the top and sides and wait about 20-30 minutes. After that, peek in on the soap. If it's in a good gel stage from side to side of the pot, open it up and scoop. But beware! While it will be much more easy to scoop, the gel-stage soap can be upwards of 200 degrees! And it's still quite caustic from the lye. Be very very very careful!!
  • Let it sit in the pot, and rebatch it tomorrow. You may not even have to add any extra fragrance in...just chop it/grate it and add a little water. This is the best choice if you haven't even been able to get the fragrance mixed in well, or if you have any sort of separation in the batch. Rebatching the recipe will make sure that everything is blended well, and that you get even saponification throughout the batch.
At one time or another, we're all going to experience a batch of soap seizing up on us. It just happens. But doing a little homework before hand (knowing if a fragrance is going to be prone to seizing) and being prepared for it, can certainly help save your batch of soap.
Related Video
How to Get 'Trace' in Soap Making
Homemade Soap From Scratch

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