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Defeating the Soap Gremlins

Large Batch Of Soap In Mold

Are Soap Gremlins wreaking havoc on your large soap batch?

Large batch soapmaking can present some different issues; read on to find out what they are and how to address them.

Ever had a batch of soap do odd things and were at a loss as to why? We at SoapEquipment thought we would share some the issues we have run across over the years as well as some of the solutions for large batch Soapmaking.

1) Volcanoing

For those fortunate Soapers who don’t know what this is, it is your soap rising up from heat buildup in a large production mold. It means you are getting maximum saponification and conversion of oils to soap and glycerin. Temperatures can reach up to 160° F to 170° F (71° C to 77° C) in a mold. Your soap will get hot, but some formulas get hotter than others.

The following items are known to create more heat:

  • Honey
  • beeswax
  • fragrances oils
  • some essential oils

If there is a dip or sag, after the volcano erupts, drag soap into the middle from the sides. Usually a ¼” (7mm) lower at the sides tapering into the middle will compensate for the sag. The same putty knife you use to line the mold works great. This can be controlled somewhat by covering the top of your mold. An inexpensive cover can be made by wrapping a piece of plastic bag around a piece of cardboard then placing it on top of the soap.

If your soap cracked a little due to heat, just before cutting a block of wood or the palm of your hand can be used to press and level out the soap as well as to close up those the cracks.

2) Soap pulling away from the sides or divider in large production molds

Sometimes soap will pull away from the sides or divider of the mold, which is typically caused by not covering the mold. The hot soap will draw away from the colder plastic and as it cools, will rise up away from the plastic, leaving a pocket. If all of the mold (sides, top and bottom) are not covered to help hold in the heat and keep the temperature even; the soap can cool prematurely next to the plastic, preventing the entire batch from rising evenly.

We recommended that you cover your mold well with a heavy moving pad, quilt, or put some Polystyrene Foam Board Insulation around the sides, top and bottom.

3) Separation

Separation can be caused when using fragrance oils or essential oils, like clove, cinnamon, rose geranium as well as other ingredients like honey and Caster Oil. Pockets of oil or veins (rivers) in your soap are typically caused by fragrance oils with too much alcohol. Heat can accentuate this. Try bringing your mixing temperature down to below 100° F (38° C). Many times this will take careof it. Test batching is always good before trying new ideas on a big production batch.

Goat Milk can cause many of the above issues listed. Though when using it in soap many of these issues can be controlled by staying below 85° F. (29.4° C) when mixing and finding just the right combination of mold covering.

The main thing to remember: All soap will heat up, but larger block pours can really heat up.

4) Edges and corners of your soap are whitish or light colored

This is caused by slowed or arrested saponification. Generally, it is due to not being insulated well enough but can also occur from the room temperature being too cold. In either case, the cold is first penetrating the mold at those points (generally the lower corners) and stops the saponification process. One mistake that is made most often when covering and insulating a mold, is forgetting toinsulate the bottom of it. Heat rises; so the bottom of the mold will cool off the quickest. Do not set it directly on a floor unless it is insulated. The cooler floor will suck the heat right out. Putting a piece of Polystyrene Foam Board Insulation or some sort of insulating material like fiberglass or even a blanket, under the mold will help to hold in the heat.

If your mold is on a dolly and the room is 70° F (21° C) or above, you might give it a try. If you experience problems then insulate it. We found in the summer that this worked just fine but in the winter we had to insulate it. Even in the tropics, this can be a problem. This happened to one of our customers in Fiji.

5) Leaking at the Corners

There are primarily two reasons your mold might leak.

First is not pouring at a medium-to-thick trace. Soapers new to pouring large batches sometimes can get a false trace. This is where the mixture seems to thicken and then once in the mold, slacks up, and goes thin. Sometimes when using Fragrance Oils or EOs that seize, we get anxious and pour sooner than we should. By testing the reaction in a small quantity of soap, you are not risking problems with a big batch. Whatever you do, pour at a medium-to-thick trace to start, then if you want to pour at thinner traces, gradually work up to it.

Second, is tightening the Wing Nuts too tight. If you have tightened the wing nuts tighter than necessary, they can bow the corners and create a leak right at the corners. I know… your first instinct is to tighten the nuts up more to stop that leak. Over tightening will eventually stress the plastic and crack it along the groove. Do not over tighten. They should be snug, just past a rattle. .

Finally, a few less likely reasons for leaks are the following:

  • Not supporting the bottom of an Air Cutter mold. This allows it to cup and draw away from the groove in the sides and ends because they are grooved to match your Loaf Cutting Grid.
  • Not putting your molds right back together after de-molding or storing in such a way that allows them to warp. It does not take much to cause even that thick plastic to warp.

Basic Information and Tips:

Here are a few more tips to help you defeat those soap gremlins should they come visiting:

  • When unmolding your soap, use a rubber mallet to lightly tap the mold sides loose from the liner paper. There will usually be a little suction holding them tight to the block of soap. After the sides are removed, tap off the end pieces.
  • Molds do not really need to be washed. They can be scraped off with a putty knife. Remember they heat up to 160-170 degrees (71 to 77 C) during saponification. Of course, you are using sodium hydroxide, which will kill anything else that might be on there.
  • If on the first try you get a slight leak, use a little soft soap to push into the outside corners, 2”, or 3” (5cm to 7cm) out each way. Pouring at a heavier trace will solve the problem.

In Conclusion

Large Batch Of Soap In Mold With Sections

As a SoapMaker, you hope to never have to deal with any of the above issues but should any of these arise, we hope you will find this information very helpful.


This article provided by, suppliers of soap and body care equipment for the handcrafted industry since 1996.

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