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Discounted water cold process method (DWCP)
This method assumes a good understanding of the basics of soap making, and is therefore best suited to soapers with several batches behind them!
For further and general background information about soap and soapmaking, please refer to my soap methods overview and my versions of hot process soap and traditional cold process method.
If you prefer to avoid altogether working with strong lye solutions, you can choose the easy road and purchase a natural soap base for hand milling, also known as rebatching or, less appropriately, as remilling.
My preferred method for determining how much water to use is based on the amount of sodium hydroxide needed for the recipe. So while most soapers refer to "discounted water" as a way of calculating the water based on the total weight of the *oils*, I prefer to use the concentration of my lye solution (water + sodium hydroxide) as a reference.
The idea of discounting water comes from observing how all soaps, no matter which process has been used to make them, will shrink and lose weight over time - and typically, this shrinking and weight loss are more noticeable when a larger amount of water has been used to make the caustic solution.
Now, water in the soap mixture has the function of diluting the alkali (sodium or potassium hydroxide) and dispersing its molecules, which can then move around and react more easily with the fatty acid molecules. In some particular cases (for instance, when sugars or alcohols are introduced in the mixture, where they act as catalysts or otherwise accelerate the "thickening" process), water is also an aid to avoid seizing - and in these cases, reducing water is a risky and usually *not* recommended practice.
Also, it is usually best not to reduce water until a certain familiarity with the soapmaking process in its whole has been acquired. Making soap with "full water amounts" (for instance, as suggested by popular soapmaking calculators such as Therese Lott's or Majestic Mountain Sage's) allows for a wider error margin. More water usually means that the chemical reaction in the soap mixture will take a bit longer to start, thus giving the soaper better chances to stop mixing at the right moment. And even before this, more water also means a weaker reaction (i.e., less problems) when diluting the alkali (sodium or potassium hydroxide). This is because, as soapmaker and chemist Susan Lewis explains,
When a strong base comes in contact with water, it dissociates (splits into its constituent ions Na+ and OH-) and is then in solution. This is a highly exothermic reaction (basically it gives out lots of heat!). The less water you use, the harder it is for this heat to dissapate. There is less liquid to absorb the heat of the dissociation so your solution is not only stronger (more concentrated), but hotter too. Which is why iced water helps, since it needs more energy to raise the temperature than room temperature water, so compensating for the lower volume of water.
On the other hand, there are types of soap and situations where excess water can be a real problem - for instance, when using large percentages of soft oils (such as olive, macadamia or avocado), or when storage space and weather conditions are not ideal, or also when soap needs to be packaged within a relatively short curing time.
When a recipe is correctly formulated and the soap mixture is properly mixed, insulated and able to completely saponify within the first 24-48 hours, discounting water speeds up the curing time. Fully saponified soap only needs curing in order to dry out, and using less water from the start allows for soaps that are ready to wrap or use within a relatively short time - sometimes as little as one or two weeks only.
In these cases, some soapers opt for an HP method. Being an incurable CP addict, I have been using a discounted water method since I started making soap (or very soon after). This subject has been discussed extensively on several mailing list, but it's been only after comparing notes with MaryElaine Chambers (Chambers' Comforts & Soaps) and other experienced soapmakers on Soap Naturally, that I decided to research, experiment and lay out the cold process method, which I call DWCP (Discounted Water Cold Process soap) and is described next.
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