Hairline cracking issue in curing soaps

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New Member
Feb 12, 2014
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Hi everyone! :wave: I am new here and hoping one of you brilliant soapmakers could lend your insights into a hairline cracking problem I am experiencing with my soaps.

I have a recipe that is similar to the 'Breaking the Rules'/75% CO, 25% CB-SB soap, superfatted at 15% and using coconut milk for half the water. I use frozen milk/water and my batter never gets above 90F degrees. To avoid gel phase, I put it in the freezer for a few hours then transfer it to the fridge for a few more (maybe 8-9 total between the two), then out to the counter where I keep it overnight. After about 24 hours it's still easy to cut. (I use pastry cutter currently and do get a bit of crumbling at the bottom edges of the bars, but am switching to a wire cutter.)

In the Autumn, I made this soap successfully in a 2# mold and recently wanted to try a 5# mold. I've made it four times now in the 5# and each time the bars develop cracks in about 1-3 days after cutting.

This last batch I did a water discount of 10% but still got cracking on day 2 of curing. I got a crack on the side of the bar along the top and another crack from the bottom up the middle. It all happens during curing.

Yesterday I went back to making a 2# batch and this morning there is a hairline crack developing a couple of the bars.

So vexing! :mad: Any thoughts as to why this is happening?

Thanks so much!!
Its possible your bars are drying too fast. Is your curing rack in a low humidity area?
Thanks for your reply, Obsidian. Yes, it's pretty dry where I live right now: 25% humidity. The soaps aren't near any heat source where they could dry unevenly but we have pretty dry Winters here.

Do you think a water discount is going to affect this issue in any way?

Please, does anyone have any other thoughts? I'd be so grateful for them!
I've had soaps crack after being in the fridge because the outside cools and the inside is still heating up. I've had cracking from low humidity too, when the outside dries faster. It could be many factors.
I make a 100% CO soap for laundry and it gets those cracks after it cools down from gel. I just assumed it was because CO gets so hot as it saponifies. I mean, uncovered and room temp, it went from pudding to full gel in less than 15 minutes (in a wooden 4lb mold.). I too live in a low humidity, cold climate but somehow I don't think it's the humidity. I think it's that hot gel phase. Maybe because it forms a skin that cracks as it cools? CO doesn't have as much elasticity as some of the other oils it seems.
I had the shampoo bar recipe crack in the middles as they cured. Not the tops, not the bottoms, but side-ways cracks in the middles. And they were HP. I think they dried too fast -- I have low humidity in my house.