CPOP stands for cold process/oven process. When you are finished creating your cold process soap and have it safely in the mold, you can put it in a warm oven to force the gel stage. One of the main benefits of this is being able to unmold your soap faster. The oven’s heat will evaporate more liquid out of the soap. It may also speed up cure time slightly, but this is best measured by weighing the soap periodically until it no longer loses weight – not by a specific time frame.
The oven process method can be tricky only because the amount of time and heat have several factors that affect the result. Too much heat can cause blistering, “alien brain” soap. A smaller batch of soap will require less heat and time in the oven, while a larger batch will require more. When I am making a small six-bar batch, I typically turn on my oven to 170 F (77 C) which is the lowest it will go. As soon as it is fully heated, I place my soap in the oven (UNCOVERED) on the middle rack and immediately turn off the oven. I can leave it there overnight and it will be ready to cut the next morning – as long as no one opens the oven door or accidentally turns on the oven in the meantime! If I have a little bit larger batch – up to 12 bars, for example – I may turn the oven off immediately, but then turn the oven light on and leave it on overnight. It’s easier to take a peek at the soap this way to make sure it isn’t overheating. It’s amazing how much heat that little bulb can create though, so if you see evidence of overheating, be sure to turn it off!
Altitude is also a factor that can make your soap heat up faster than you intended! I asked Debi Olsen of Me Do it Meself how she does oven processing since she lives in the mountains of Colorado. Here are her methods: “My oven only goes as low as 170 degrees, so I preheat and immediately turn it off, then crack the oven door for about 10 minutes before I put my soap in. I let the oven cool down on its own and leave it in for at least 8 hours.”
What if you overheat your soap? I had blistering, alien brain soap in a large slab mold once. The soap underneath was actually fine, so all I had to do was plane off the blistered soap to reveal perfectly beautiful soap underneath. This may or may not work, depending on how deep the blisters go, but it would be worth trying! If you use a silicone liner, you might also end up with some interesting textures on the surfaces of the soap that touch the silicone. These are usually just cosmetic and you can plane them off also if you wish.