Is too little water possible?

[Dani993]

So, after a half dozen batches of CP soap, I decided that I was ready for (true) Castile .

I used SoapCalc.net to figure out how much lye to use, with a 40% lye solution and a 3% superfat (I was already feeling impatient with the 4 -6 month cure period, so I thought, less water/superfat, less cure time). All the warnings about too strong a lye solution almost scared me off, but then I calculated the recipe I've been using (out of a book) which is 35%.

So, fine. I went ahead and did it, and it looks beautiful . I tested it after 24 hours and it was pH of 7.5-8.0 (WIN!!). When I cut it, it was quite hard and crumbly. Which I was NOT expecting - this is the hardest (i.e. firmest, not most difficult) soap I've made, even though I've used 60-70% solid fats previously.

That got me to thinking: Can you use too little water? Because I could have used less water than I did. And I'm not really looking safety-wise, I know it's more caustic; I'm looking soap-quality-wise.

If I could make a lye solution of, say, 55-60%, would that make the same quality soap with a faster cure time? Or would it mess up the soap, or just degrade the quality? (This is, of course, considering that I'm using a proper NOT-lye-heavy recipe).

 

[Obsidian]

The amount of water really doesn't have much to do with cure. While less water will help the bars harden/dry faster, there is more to curing then just drying. Nothing you do will replace a proper cure for any soap. Castile can be used after 4 weeks like any other soap but it does get better with age, increased bubbles, less slime etc..

Yes, you can use too little water but I'm not sure what the limit is.

 

[DeeAnna]

"... And I'm not really looking safety-wise, I know it's more caustic..."

NaOH dissociates (splits apart into Na+ and OH-) almost completely whether you make a 28% solution or a 50% solution. The safety issues are the same regardless of concentration. If a soap maker spills a less concentrated lye solution on her skin, she'll be in just as much trouble just as fast as if she spills a more concentrated one.

"... Can you use too little water?... ...If I could make a lye solution of, say, 55-60%..."

Yes. It is not physically possible to make a 55-60% NaOH solution -- you literally cannot dissolve that much NaOH in water under normal conditions. The absolute max at room temperature is about 52% NaOH, and I would never push it that far. A 50% solution is the practical upper limit for soap making purposes, but it will take additional time to dissolve the lye completely when it's that concentrated. Many people back it down to 40% as a more reasonable limit.

"...a faster cure time?..."

The rate of water loss from a soap bar, which determines the cure time, is about the same whether you use a less concentrated lye solution or a more concentrated one. The main difference is the total amount of water in the soap to begin with -- less water tends to mean the soap is somewhat harder, all other things being equal. See: http://www.soapmakingforum.com/showthread.php?t=38161 and http://www.soapmakingforum.com/showthread.php?t=40599 for more info. The bottom line is ... cure time is not shortened much, if at all, by using less water in your recipe.

"...I tested it after 24 hours and it was pH of 7.5-8.0 (WIN!!)...."

A home pH test done on bar soap with test strips or whatever is notoriously unreliable. Done correctly in a chemistry lab with a standardized testing procedure, the pH of a solution with properly made castile soap (olive oil, water, and lye only) will be in the 10 to 11 range. You can use a home pH test to look for trends, but you can't rely on the actual numbers to tell you if your soap is safe or lye heavy. The "zap test" is a much more reliable method of finding that out, short of setting up a chem lab in your basement.

 

[shunt2011]

Deanna, you are my scientific hero here. I thought the posters PH was wrong. I've always been told and understood soap to generally run between 9-11 ph wise.

 

[new12soap]

Yes, you can use too little water. The water not only holds the lye in solution, it acts as a vehicle to help the lye interact with all the fat to make soap. A 50% solution is possible, but not a good idea. 40% is the absolute minimum I would recommend.

Cure time is not determined by water content, I don't find that a castile made w 40% is any better any faster than one made w 33% solution.

 

[ilovesoap2]

I plan to cure a minimum of 3 months, but I can't help but wonder how a soap this bone dry and at 6 months old just falls apart. I read in another thread:-o

 

[Dani993]

Thanks for all the info!! I definitely have a better appreciation for curing.

My solution is to just make soap more often, so I have batches coming off the cure more often

I think I will run my own experiment on using them before the cure is up, so I have personal reality of how the soaps feel then.