Is one better than the other? It depends on what you like. Do you prefer soaps with lots of color, swirls and edible looking or do you prefer to keep is simple? I make both hot and cold process soaps and I am often asked, What's the difference? Does it matter if it is cold or hot? The only difference is the method of making the soap.
Here is the best way to explain the difference.
Chamomile Neroli Hot Process Soap
The hot process and cold process but lets start with the hot process. It begins by running your recipe through a lye calculator. It measures how much lye that will be needed in your recipe. The lye is measured and added to your measured water NOT THE OTHER WAY AROUND because adding water to lye is dangerous and can cause an eruption. Next, the lye and water mixture is added to heated vegetable or animal fats. Some soapers prefer to use a crockpot and some prefer to use a pot. I use a pot as my crock pot is never big enough and prefer a larger pot which gets put into the oven.
The lye/water and oil mixture gets blended together with a stick blender for a while before adding any desired extras, such as the oatmeal, orange peel, etc. The mixture is then stirred a little more to make sure that everything is evenly distributed. Next, the pot goes into the oven at about 180 degrees I usually go a little bit higher. It then gets cooked. The first 20-30 minutes the mixtures starts to go into a gel phase and you are stirring during this time. Then it goes back in for another 20-30 depending on how it looks because you have to go by how it looks. Once it has reached the gel/applesauce look, it then morphs into a kind of mashed potato look. Then the soap is almost done.
Ok so how do you tell if the soap is done? Good question. As I said before it will begin to look like mashed potatoes but to be really sure I take just a tiny bit of of the soap and do the tongue zap. If it stings a little then it needs to go back in. I try not to do that very often and just use my eye and test the soap under the water to see if it starts to lather.
The soap is very thick like mash potatoes and it will be hot so I let it cool down some before I start to add my fragrances. I then add the color. I tried adding color before I put it into the oven and it was not good so I know better to use coloring after the soap has come out of the oven.
True Lavender Soap
The cold process is very similar to the hot process, except that the lye/water and the oil fats area blended together, fragrance, color and other additives are added when the soap gets thick like a pudding and then poured directly into the mold. No heating in the oven. So you just bypass the heating the mixture in the oven. It just goes straight to the mold. A plastic wrap can be put over the mold to keep from ash forming on top of the soap and then a towel or blanket to cover it. I would say within an hour or two the soap will begin to heat up in the mold. This is where the heating process stage begins for cold process. This can last for a few hours depending on the size of the mold and the soap. Sometimes soapers will blend their colors in the pot before adding to the mold and some add color when it is in the mold to swirl and give it a little pizzaz. Many soapers have their own way of coloring their soaps so it is up to the individual. I usually like to add the color before adding to the mold as my swirling techniques really suck.
Both the cold and the hot process rely on lye, which is a very dangerous chemical that can burn skin on contact and is fatal if ingested. Therefore, people who use lye to make soap need to be very careful and follow detailed directions. Many people have tried to find a way to make soap without using lye, but this is impossible. Even the soap in the melt and pour soap kits was processed with lye, although people using these kits do not have to handle the lye themselves.
Traditional soapers might prefer the hot process, which is the oldest method that humans have used to make soap. Some prefer the cold process method as some claim to have more conditioning properties and the smooth texture vs the hot process which can have a more homemade rustic look. I don't think one is better than the other I just prefer the hot process as it is much quicker for me.
The curing time for hot process soap is hardly any. I like to let mine cure still for about a week so they are nice and firm before using where as cold process soap is cured for 4-6 weeks to expell any extra water from the soap and to hardened.
Which method do I prefer? I prefer the hot process soap as it is quicker but I do like the smooth look of the cold process method as well. Hot Process looks natural to me and don't have to deal with trying to make the soap look to pretty. I want people to use them not marvel over how pretty they look. And I don't like to make my soaps look edible (even though some turn out that way) So I try to keep them simple.
There you have it. My best way to explain the difference between the two methods.