Thursday, November 19, 2009

Hot and Cold Process Soaping Methods

If you know anything about handmade soap, you may have run across this terminology before: cold process, hot process, melt and pour, hand milled...

You may not know what any of that means.

In case you ever wondered, this is the blog read for you.

Well, here is my attempt at briefly explaining what those things are and how they differ from one another.


Let's start with just your basic melt and pour. This is a method of soap making where you purchasing a pre-made soap product. You melt it down, add some color and frgrance to it and mold it to your preference. Sound easy? It is, although there are a few things that you need to know in order for your soap to be successful. Melt and pour method does not require you adding any ingredients that may be dangerous around kids and animals, or to yourself. It really is a fun, clean craft. Easy wash up since it IS soap.

I started off making melt and pour soaps. I still make them on occasion, although that method is not the bulk of my soap making.


Next is the cold process soap method. This requires that your make your own soap formula from various oils, liquid and sodium hydroxide (lye).  There are tons and bunches of soap recipes online and in books. Each oil adds its own distinctiveness to the soap recipe. If your are a star trek fan, you may remember how "The Borg" assimilate other cultures to add to their own? Well, different oils are like that in soap. Palm oil helps to harden the soap, coconut oil gives the soap a nice lather, castor oil gives the soap a sudsy quality, olive oil is amazing on your skin but low on suds, and so on.

Just the right amount of liquid and lye mixed with the oils, and mixed together until the soap begins to thicken just a bit, called "trace". Then you add any other colors, fragrances or exfoliants to the soap. In cold process, the lye mixed liquid and oils are mixed together at a cooler temperature. They are poured into molds and covered and insulated to allow the oils and lye mixture to heat up and "cook". The curing process takes a while before the soap is safe to use. I typically wait about four to six weeks before I will allow it to be sold.

If done right with a good recipe, you will get a great, smooth bar of soap at the end of that time.  A few drawbacks in cold process is that some colors you may use, may look different when the soap is done, and some fragrance oils fail miserably during the curing process and you end up with a nice bar of soap that doesn't smell anything like you intended.


Hot process soap uses essentially the same ingredients as cold process, although you may want to add 2.5-5% additional liquid to your recipe to prevent the soap from hardening a bit too quickly. Sometimes you can add just a bit of sugar to prevent hardening too quickly also.  Each hot process soaper develops their own style.

This time you take your lye/liquid mixture and add it to your oils. Then, you begin to heat up your soap mixture. There are a variety of different ways to do that. Some soapers use their oven, some used a large crockpot, and some are double boiler experts. I'm a crockpot fan myself and own several crockpots so that I can make more than one batch at a time.

The soap mixture is heated up slowly and on low heat since you don't want to burn the stuff. It is important to check on it while "cooking" to avoid boiling over and spillage. The soap will turn from a batter-like substance to a slightly lumpy gel (kind of like thickened wall paper paste or thickened fiber laxative like metamucil...really! :)  Once the soap is this gel substance, you can give it a taste test. Yes, I said a taste test. Before taste testing, I test it between my fingers first, then if it feels OK, I touch it to my tongue. If there is no stinging "zap" to the taste of the soap, that means it is finished cooking and you can take it out and allow it to cool. I usually add my color, fragrances and any other additional oils or ingredients once it has cooled just a bit. This allows the fragrance to not overheat in the soap dissipate. Once I'm done with that, off it goes to my mold. No need to cover it up to insulate and cook; you've already cooked it. Once the soap hardens, it is ready to use.

The benefits of hot process is that you have soap that is ready to use right away because cooking it has allowed the chemical reaction between the lye and oils to occur more rapidly.  Another benefit is that you don't have worry near as much about your fragrance oils changing during the cook, since you add them AFTER the chemical interactions have occurred. The drawback to hot process is that you can't get that gorgeous, color swirl effect in it like you can with cold process, although you can mix a few colors together if you like.


Hand millled soap is a fun little process where you use soap that has already been made and you shred it down, add a bit of water, and melt it down. You then take your colors, fragrances and other additives and add it to your soap, re-mold it and allow it to dry and harden again. Some folks make hand milled soap balls, or bars out of soap that maybe didn't look too nice the first time around for some reason. Hand milling gives a bar of soap a second chance. I love using hand milled soap for decorating and for adding ingredients and fragrances to my fragrance free soap. I can take a small batch and re-color or fragrance it according the season. So, it is great fun.

So there you have it. In a nutshell, some different handmade soap processing methods. This blog write was not intended as a tutorial for how exactly to make each type, but simply an overview. Hope you enjoyed.

Of course for a full list of soaps that I currently have available in many of these methods, visit one of my online shops.


Celine Blacow said...

Interesting thread.. not sure you covered glycerine soaps so effectively as the other types .. there are many variations that can be achieved from the basic formula and there is a whole art in creating soaps from glycerine bases. The melt and pour and that's it is simple yes, but most dedicated glycerine soapers put in far more work than that and add more ingredients to individualise their end products.

Good article though, apart from that.

Trish's Soapy Blessings said...

I agree, Celine, I did not give melt and pour soaping its due honor in this article. It IS quite an art to develop some of those beautiful soaps with so many added ingredients, colors and fragrances that make them unique and as an expression by the artist making them. I've spent many an hour at melt and pour and appreciate the hard work that is put into them.
My apologies for not reflecting the beauty and hard work that is put into the melt and pour soap making method.

Celine Blacow said...

I'm sorry if I came across a bit ... I don't know, tough maybe? It's just that, as a glycerine soap handcrafter, it can be that some soap makers think that it's far too simple a craft. As with other soap making, it takes time and energy (and money!) to learn how to do it right, and how to find your own groove and rythm in how to do it. Unforunately there are some out there who really think that it's the easiest thing in the world and think they can sell anything they make - thereby bringing disrepute on others who try to achieve a far higher level of crafting and luxury with their glycerine soaps. I like to think my soaps are little pieces of art and I will only sell those that I am happy to use myself and I am satisfied with - my site is available here I love your examples of other soap making and the pics are amazing. Sorry if I came across as too tough.

Trish's Soapy Blessings said...

No apology needed! Your soaps are absolutely beautiful and have such artistry! :)
I began soaping by melt and pour, but I had a very specific idea in mind when I began. I was researching how to make soap for a novel I was writing, so got myself into other methods of soap making. Melt and pour was my diving board into it though and I still make lots of different MP soaps regularly.