One of the common questions that inexperienced soapers often ask is how can the cure time be reduced? The common response from more experienced soapers is that there are no reliable shortcuts to curing soap.
Part of the curing process involves gradual chemical changes that reduce the pH, increase the mildness, and increase the lathering ability. Another part of the cure involves the physical process of drying which increases the soap's hardness and its useful life and stabilizes the soap's size for ease of packaging.
The drying process can be accelerated some with good ventilation, low humidity, and gentle warmth. The soap must still be allowed to dry slowly enough so internal moisture has enough time to migrate to the surface. If soap dries too fast, the soap can "case harden," which means it develops a hard outer rind that seals the surface and prevents internal moisture from evaporating. The bars may also warp and distort.
I did a simple experiment this May and June to measure the weight loss from two soap bars. I assumed the loss was from water evaporating from the bars.
One soap (all-veg) was made with high-oleic safflower, palm, and coconut oil with a dab of sunflower and castor (listed in order from the most to the least). The water phase was coconut milk and distilled water. I included the fat content in the milk as part of my oil phase and lye calculation. The rest of the coconut milk made up most of the water phase for my recipe. The vegan soap was made with a 30% lye solution concentration.
The other soap (beer-lard) was made from lard, HO safflower, coconut, again with a dab of sunflower and castor (again listed in order from most to least). The water phase was 100% beer, and I used a 33% lye concentration for this soap.
I used a CPOP method to saponify both soaps -- the molded soap was heated at 170 deg F for about 1 hour.
I stored the soaps out in the open on the counter in my bathroom. This bath gets steamy only once a day when DH and I shower; otherwise it gets good air circulation. It is a convenient place to do this experiment and safely out of the way of people and pets. The weather was cool and wet during much of this time. I weighed the soaps on a digital scale that reads to 0.1 gram.
Both soaps showed the same trend in weight loss. There was a big reduction in weight from day 1 (the day the soap was unmolded and cut) through day 14, a moderate loss from day 14 through day 34, and a much slower loss after that. For the math geeks, the data fit a logarithmic trend at R=0.99.
I suspect in the winter with low humidity in the house, the rate of moisture loss might be a little higher. Even so, I would say a good rule of thumb is to allow about a month for moisture levels to stabilize. That doesn't mean the soap is fully cured for the best lather and mildness (see my Post 11 below for more on that), but it does mean the soap won't change much in size and the moisture content will be reasonably stable.
Part of the curing process involves gradual chemical changes that reduce the pH, increase the mildness, and increase the lathering ability. Another part of the cure involves the physical process of drying which increases the soap's hardness and its useful life and stabilizes the soap's size for ease of packaging.
The drying process can be accelerated some with good ventilation, low humidity, and gentle warmth. The soap must still be allowed to dry slowly enough so internal moisture has enough time to migrate to the surface. If soap dries too fast, the soap can "case harden," which means it develops a hard outer rind that seals the surface and prevents internal moisture from evaporating. The bars may also warp and distort.
I did a simple experiment this May and June to measure the weight loss from two soap bars. I assumed the loss was from water evaporating from the bars.
One soap (all-veg) was made with high-oleic safflower, palm, and coconut oil with a dab of sunflower and castor (listed in order from the most to the least). The water phase was coconut milk and distilled water. I included the fat content in the milk as part of my oil phase and lye calculation. The rest of the coconut milk made up most of the water phase for my recipe. The vegan soap was made with a 30% lye solution concentration.
The other soap (beer-lard) was made from lard, HO safflower, coconut, again with a dab of sunflower and castor (again listed in order from most to least). The water phase was 100% beer, and I used a 33% lye concentration for this soap.
I used a CPOP method to saponify both soaps -- the molded soap was heated at 170 deg F for about 1 hour.
I stored the soaps out in the open on the counter in my bathroom. This bath gets steamy only once a day when DH and I shower; otherwise it gets good air circulation. It is a convenient place to do this experiment and safely out of the way of people and pets. The weather was cool and wet during much of this time. I weighed the soaps on a digital scale that reads to 0.1 gram.
Both soaps showed the same trend in weight loss. There was a big reduction in weight from day 1 (the day the soap was unmolded and cut) through day 14, a moderate loss from day 14 through day 34, and a much slower loss after that. For the math geeks, the data fit a logarithmic trend at R=0.99.
I suspect in the winter with low humidity in the house, the rate of moisture loss might be a little higher. Even so, I would say a good rule of thumb is to allow about a month for moisture levels to stabilize. That doesn't mean the soap is fully cured for the best lather and mildness (see my Post 11 below for more on that), but it does mean the soap won't change much in size and the moisture content will be reasonably stable.
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If you are using purchased coconut milk, I can help. Here's how I figured the amount of coconut oil that was added by my coconut milk:
