Why does soap need to cure?

The majority of the soaps made for Homestead Soapery are cold process (CP) soaps, but we also do some work with pre-made bases, called melt and pour (MP), especially when testing scents and exfoliants. The reason we do this is to verify and understand the different ways that exfoliants and scents hold up in soap and whether or not we want to use them in bigger batches.

Cold process soap has a different consistency to melt and pour bases, so sometimes testing is not 100% accurate. This is because the viscosity of the batter in cold process is dependent on the soaper and the particular design requirement they are going for.

When using MP bases, often a soap is ready for use within 4-6 hours, long enough for the batter to resolidify after adding additives to it. It can still benefit from a cure time, which we have found has made a nicer bar overall in any MP soaps we have made during testing.

When creating a CP soap, the soap needs to cure for at least 4-6 weeks for most bases, and up to 4-6 months for pure castiles. Think of curing soap like curing firewood – the water in the item needs to evaporate to make it harder. Cured soap produces a harder bar that lasts longer between uses, has a milder touch on the skin, and is a more finished product. Recently, I finished using an olive oil soap made from about 50% olive oil. With regular showering, this soap lasted as a body soap for 6 weeks. Granted, the scent has long since left, which is standard in hand crafted soaps (and I purchased it this time last year), but the bar still performed its duty with a nice lather and lovely silkiness on the skin afterward.

One of the reasons soap needs to cure is to ensure that saponification has completely occurred. Saponification is the chemical reaction that occurs when oil reacts with a lye water solution to create an actual bar of soap. Generally, saponification will occur within 24-48 hours which means that the pH changes related to the process happen within the first 48 hours of pouring. What this means is that the soap is safe to use, and there is no lye floating around that could harm a user.

The more primary reason soap needs to cure is to harden the soap. Hardening the soap means that through the curing process, water slowly evaporates from the bar which causes the soap to harden. A harder bar of soap will last longer, produce more lather, and in general be a much better soap to use. It will wear over a longer period of time, meaning you will have more soap to use.

The exception to this rule is a castile soap which is a soap made using olive oil. It is presumed that any soap batter with more than 50% olive oil (though some say anything over 40%), and up to 100% is considered a castile bar. These bars can take 4-6 or even 8 months to harden to give you the absolute best bar possible. Even after pouring, these soaps take longer to unmold and are much softer. I only just cut Booch after waiting for 5 days and she was still a bit soft!

So you see, this is why we will be releasing soaps in batches. Not only do we need to let them cure, but we need to let them harden. We want you to have the best experience using our soaps, and we don’t want to prematurely impact that by selling you a soap too early.

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