Gelling with Sodium Gluconate and other Salts

[Megan]

I am having issues getting my soaps to fully gel since switching over to Sodium Gluconate as a chelator. Actually, I was having similar problems when using Sodium Citrate as well. I usually soap at 90 Fahrenheit at the lowest, and more often around 100-110 F. Then I usually CPOP with the oven set to 170 F while babysitting the loaf, checking every 10-15 min to watch it go through gel phase.

In the past, when I wasn't using a chelating salt, this process would take about an hour, but usually it would go through gel by 30-45 min and at a relatively low temp (like 130-140 F). Now it's taking much longer and it seems to gel at a higher temperature. If it gets near 150-160 F, I usually take it out as I fear it's going to overheat (actually, I know it's overheating some, because I will sometimes get very small pinprick dots of zappy lye leakage when I cut the bars a day later). Sometimes by this point it still hasn't gelled or has only partially gelled and never finishes. I'm quite frustrated!

So I guess my question is...is gel more of a temperature thing, or is it more of a time thing? Any suggestions for promoting gel other than what I'm doing? Would a longer time keeping it at a lower (but still warm) temperature be better?

Or maybe I should just stop trying to gel altogether!?!

 

[DeeAnna]

Gel is a phase change from a solid to a type of liquid. It occurs based on temperature. It's roughly the equivalent of ice melting into liquid water. Ice will melt at the same temperature regardless of when the ice reaches that temp.

The temperature at which gel happens will vary depending on the fatty acids, water content, etc. in the soap. If you make multiple batches all with the same formulation, the gel temp should be reasonably consistent from one batch to the next.

But the gel temp for one particular formulation will not necessarily be the same as the gel temp for another, so if you change the fats or the water content or the other additives, it's likely you'll see changes in the gel temp.

As to whether you have to SEE evidence of gel every time, I'm increasingly convinced that's not strictly necessary. It's nice from a human point of view, but not required for the chemistry. I've had many batches of soap that don't show visible signs of gel on the surface of the soap, but the soap otherwise looks and feels the same as soap that did show visible signs on the soap's surface.

An analogy of why this might be the case -- Think about melting a stick of refrigerator-cold butter in a microwave. If you've ever tried it, you may have learned the stick can look perfectly solid, but when you touch it, the outside skin opens up and the hot,melted center pours out. IMO, soap can do much the same thing -- it can be warm enough to reach its gel temperature, even though the surface of the soap may still look solid.

When you heat a batch of soap for a long enough time at 170 F, you're risking the soap overheating, as you have already mentioned. The heat from saponification will take care of warming the center of the soap, however, so there's no real reason to bake it at 170 F.

In recent years, people have shifted their thinking about CPOP. It's now used mainly to keep the outside surfaces of the molded soap sufficiently warm. The oven temp does not have to be hot enough to force the soap into gel, because the heat generated in the center of the soap will take care of that.

That is why many people now preheat the oven to about 140 F, turn the oven off, put the molded soap in, and leave the soap for at least a few hours. Other ways to accomplish this goal are insulating the molded soap with blankets or in a cooler or using a heating pad.

 

[Megan]

So do you agree that the addition of a salt would change the phase change temp? Like we see when we add salt to water?

It makes sense in this regard... but in the case of adding salt to water, it decreases the freezing point...but what I'm seeing is the opposite. Not to mention, soap is already a salt.

Regardless, I will try a lower and slower approach to gel going forward to see if I get better results. If not, I guess moving to an ungelled soap isn't the end of the world.

 

[DeeAnna]

"...the addition of a salt would change the phase change temp? Like we see when we add salt to water? ...

I imagine this would be so, but I haven't done any practical experiments nor studied the chemistry to know for sure.

I remember the freezing point depression and boiling point elevation rule. But keep in mind this rule applies to simple ionic solutions. You can't assume basic rules of chemistry always apply when talking about soap. Some do, but you can't assume they all do.

Soap, while it is indeed a salt, will behave differently than sodium chloride. Soap molecules in a bar or loaf of soap are going to largely be in a molecular form, not a dissociated (ionic) form. Soap molecules won't dissociate unless the concentration of soap in water is sufficiently low. Table salt almost entirely dissociates when dissolved in water.

I also know the rules of solubility in water aren't the same as the rules for solubility in a highly alkaline solution. That's true for soap and even for table salt. I also know EDTA solubility changes dramatically in a lye solution compared with plain water.

edit: "...I guess moving to an ungelled soap isn't the end of the world...."

Well, I'm not sure you have to go to the other end of the spectrum. I don't like ungelled soap because it's usually too soft and clay like, so my strong preference is for soap that has gotten warm enough (aka gelled).

That said, I rarely do anything to deliberately force gel. I seldom even use the "preheat to 140 and turn it off" CPOP method. Usually I soap around 95-100 F and only lightly cover the molded soap with a cotton "tea towel" to keep the dust out and a bit of warmth in. In winter, I might use a thicker bath towel because my house is cooler.

Even though I'm rather laid-back about this, I seldom have a problem with the soap being ungelled, and when it does happen, I know how to fix it.

IMO, a person can ensure the soap stays sufficiently warm without using a "heat to 170 and hold until visible gel" method of CPOP and still get reliable, good results.

 

[Megan]

I'll agree that I do much prefer gelled soap, due to the hardness and ease of unmolding.

Thanks for the advice!

 

[Megan]

Update:
I've started turning my oven off at 140 F and putting the soaps in for the last two batches I've made.
I have noticed that my overheating problems are over for now, so I am pleased. I'm having a few issues with the outside of the soap gelling, but I think this is due to not leaving it long enough (I soap at night and have anxiety about leaving anything in the oven overnight when I go to sleep...lol, probably something I just need to get over)

 

[DeeAnna]

If you now turn your oven off to CPOP, that eliminates the safety risk of running the oven without you being nearby. So that should be a reassurance, right?

If you worry about forgetting the soap since it's hidden away in the oven, I can appreciate that one -- been there, done that. I've learned to put something over the controls so I can't turn the oven on absent-mindedly. I put a big refrigerator magnet on the control panel for my new oven, but a Post-It note or something like that would work too. That helps a lot.

 

[cmzaha]

I never put my soap in the oven but I do use a heating pad and hat blanket to cover my gelling crates. As DeeAnna mentioned I very seldom see physical changes on the outside to indicate my soap is gelling. In fact, if I do it usually means it is overheating and I remove the heat source, take the mold out of the crate, put it on a rack with a fan aimed towards the mold. I use my method because it works for me and I cannot cover my soap any way other than putting them in a crate, since I pour to the top. I do not take temps, I just know what it takes to gel my soaps.

I will mention I have never found any difference in gelling when using SG, EDTA or the SG/EDTA combo I use in every batch and I gel every batch.

 

[Peachy Clean Soap]

I never put my soap in the oven but I do use a heating pad and hat blanket to cover my gelling crates. As DeeAnna mentioned I very seldom see physical changes on the outside to indicate my soap is gelling. In fact, if I do it usually means it is overheating and I remove the heat source, take the mold out of the crate, put it on a rack with a fan aimed towards the mold. I use my method because it works for me and I cannot cover my soap any way other than putting them in a crate, since I pour to the top. I do not take temps, I just know what it takes to gel my soaps.

I will mention I have never found any difference in gelling when using SG, EDTA or the SG/EDTA combo I use in every batch and I gel every batch.

I too don't put my soap in the oven' my oven it doesn't retain the heat long enought for my soap to reach gel w/ out watching it constantly adjusting the heat by opening the oven door non-stop' personally i've found a heating pad & covered in a cupboard is perfect tor my soaping preference to reach the gel stage.