Do you love making cold processed (CP) soap but hate the wait of weeks
before you can use your creation? Hot processed, or HP, soap is a
wonderful way to use all the same ingredients you use in your CP to produce
a soap that, like Melt and Pour soap, is ready to use as soon as it cools.
There are several different methods for hot processing soap. The oldest
is direct-heat HP, which is what most people think of -- it means putting a
pot of soap on the stove to boil, stirring it constantly until it gels and all
the water is evaporated. This method is relatively easy as long as you can
endure stirring for an hour and a half while wearing elbow-length rubber
gloves, eye goggles, long sleeves and pants, and an apron. :) If you're like
me, however, and aren't so fond of constant stirring, you might like using the
closed-system method, abbreviated CSDBHP (closed-system double boiler hot
The CSDBHP method is relatively young. Its origins as I know them stem
from one soaper adapting Catherine Failor's double-boiler gel acceleration
instructions in her book Transparent Soapmaking to straight hot-process
soap. If you can make CP, you can make HP using the closed-system method.
- How many orders have you had to turn down because you couldn't turn
around the soap order in less than six weeks? Hot processed soap is ready
for sale in a week or less.
- The time involved to make the soap varies little, from a tiny batch
to a huge one.
- Save money on fragrances! You use as little as half as much scent for
HP soap as for CP. Also, volatile essential oils are less likely to be
changed by the high alkalinity of raw CP -- you can be reasonably assured
your tea tree oil is as effective in the finished soap as it was before
you added it.
- You can put your soap on to cook and still do other activities while
- It's easy and fun!
Safety equipment: goggles, gloves, apron, vinegar.
You should have one pot large enough to accommodate a doubled-in-size
version of your regular soap batch, as the soap expands during heating.
This pot must be stainless steel, glass, or undamaged enamel ware as it
will be coming into contact with the lye. You should also have a larger
outer pot that can comfortably fit your soap pot inside it with a
firmly-fitting lid. There should be an object that the inner pot sits
on to keep it from touching the bottom of the outer pan -- glass marbles,
forks, small rocks, or tuna cans work well for that. It is important
that your pots do not touch on the bottom, because if your inner pot
comes into contact with the bottom of the outer pot it can scorch or
burn your soap. I use a 20-quart stock pot for the outer pot and an
8-quart stainless steel pot for the inner, both with glass lids to help
me resist peeking. :)
I prefer using a gas stove, but electric stoves and hot-plates work just as well.
Heat-resistant spoon or wire whisk.
Thermometer with glass or stainless-steel probe.
Soap ingredients: oils, water, lye, colorants, fragrance, and additives as desired.
- First, add several inches of water to your outer pot. Bring the water level
up to the point where the soap level in your inner pot will be once immersed in
the water. Put this water on to heat to a boil.
- Make soap as you usually would for cold process: dissolve your lye in the
distilled water carefully. Melt your oils. You do not need to worry about
temperatures with hot process, so you can combine the oils and lye solution in
your inner pot as soon as both are ready.
- Mix the soap to trace, using a stick blender if you prefer.
- Once the soap is traced, and the water in the outer pot is gently boiling,
immerse the inner pot into the outer pot. Cover both pans tightly with lids.
Set your timer for 30 minutes, and go do something else until the buzzer goes
- At the buzzer, check the water level in the outer pot to make sure it is
still higher than the soap level in the inner pot. Do nothing to the soap in
the inner pot (not even peeking!). Recover the pot and set the timer for
another 30 minutes.
- In 30 minutes, check the water level again. At this point, your soap is
most likely fully saponified. You may check the soap by dunking a plastic spoon
or toothpick or something small and disposable into the soap gel and trying a
tongue-test on the small sample.
- We will continue cooking to evaporate most of the rest of the water. Set
the timer for another 30 minutes.
- When the buzzer goes off, come back and take the temperature of your soap
by setting the thermometer into the middle of the soap gel -- make sure not to
touch the bulb or tip of the thermometer to the pan. It will probably be
somewhere around 170*F at this point. It should look like a thick,
- If you want to do so, this is the point to add colorants. Dissolve your
dye or pigment in a small amount of oil or liquid and blend this into the soap.
(Note: If you use a dye which typically changes color due to the high alkaline
pH of cold process soap, such as FD&C Blue #5 which turns purple, this
will not occur. Once the soap is fully saponified, the pH level
stabilizes.) Colorants may be added at trace, but some of them may mutate due
to the high processing temperatures the soap experiences.
- Let the soap cool until its temperature is closer to 140°F. At this
point, it is fairly safe to add your fragrance without worrying that the heat will
burn it off. Since fragrancing HP at the end of the cook avoids exposing
fragrance to the high alkaline pH of CP, you will find yourself able to use much
less fragrance than you normally might -- start with half the amount of fragrance
you normally use, and adjust it as necessary for future batches.
- In order to make the soap slightly more pourable, you may choose to add a
very small amount of extra oil or water. Keep this to as small an amount as
possible, as any added water will increase your cure time or any added oil will
make your bar of soap slightly softer. Extra water can also lead to "shrunken-head
- Finally, your soap is finished and ready to be molded! Since your soap is
much thicker than CP, it is prone to getting air trapped in it as you mold it,
leaving little holes in your finished soap. To prevent this, add your soap to your
mold in thin layers and bang it down on a hard surface (such as the counter or a
tabletop) between layers to flatten it and release air bubbles. Think of it as
stress-relief therapy. :)
- Let your soap cool. It will harden as it cools. After it is fully cooled,
you can release it from the mold and slice it into bars. It is good to leave the
bars out in the air to finish curing for a few days. During this time, they
will continue hardening and become less tacky to the touch.
- Again, If you use a dye which changes color due to the high alkaline pH
of cold process soap, such as FD&C Blue #5 which turns purple, this
will not occur because the pH level has stabilized by the end of the
- Colorants may be added at trace, before cooking, but some of them may
mutate due to the high processing temperatures the soap experiences. It is
best to try this in relatively small batches so you don't face too much of
a loss if your colorant does mutate.
- DO NOT short your water! Even if you typically shorten the water amount
required for cold process, do not do so in your HP. A good amount of water
to use is 6 ounces to each pound of oils. Water facilitates the saponification
process, and if there is not enough water, some of the lye is likely to be
left unsaponified, which means you end up with a harsh soap. Adding extra
water before the cook is fine, and is perhaps advisable with batches smaller
than 3# because in such small batches the water can boil off before the lye
has a chance to fully saponify. If, after 60 minutes of cooking, your soap
seems dry-looking or you get tingles when doing the tongue-test, it is okay
to add a few ounces of water and continue cooking.
- Be very careful that your inner pot can accomodate your size batch of
soap. The soap expands during the cook and overflows can be a real mess to
clean up. If you're in doubt, take the full amount of oils and water and
fill the pot with twice that amount of water.
- Most molds that you use for CP or M&P can be safely used with CSDBHP.
Since the temperature of CSDBHP is relatively low compared to direct-heat HP,
you can use your pretty cavity molds like Milky Way molds. Be careful to fill
them slowly and thump them on the counter to release air bubbles and help
cool the soap to avoid warping the mold. Keep in mind that hot-processed
soap does not have the same shrinkage margin built in to it (because the water
is already all evaporated out), so recipes with hard oils such as palm oil,
stearic acid, tallow, coconut oil, or palm kernel oil work best. I once made
a 100% olive batch and molded it in cavity molds - and three months later I
scraped the soap out with a spoon because it wouldn't come out! :)
- Yes, you can make hot-processed milk soaps! If you don't mind a taupe
color or are using a fragrance oil that discolors (such as Vanilla), you can
add your milk as a liquid before the cook. If you want a creamy-colored soap,
add small amounts of milk before pouring, or try adding a combination of
powdered milk and a small amount of liquid or oil. Keep in mind that adding
too much liquid to the finished soap can lead to "shrunken-head syndrome."
- Just about any recipe that you use for CP can be used for HP. Just
ensure that you have enough water, and you have a good mix of hard and soft
- Certain ingredients will cause your HP to darken in color. These
ingredients are usually ones that are high in sugar -- sugars carmelize (turn
brown) -- such as milks or honey. These ingredients might be added after the
cook to preserve the coloration of the soap.
If you are comfortable with making CSDBHP, it's a very small step from
there to making transparent soap from scratch. I highly recommend Catherine
Failor's book Transparent Soapmaking if you are getting ready to
branch into this fun variety of soapmaking, because she shares a great deal
of information and tips, as well as offers many different recipes, in this
book. You can purchase it from www.borders.com or many other booksellers.
To make transparent soap, you add solvents, such as sugar water, glycerin,
and ethyl (grain) alcohol, to your soap at the end of the cook. You continue
gently heating it until the soap is completely dissolved, and then your pour
and mold it as usual. It's easy!
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