Thursday, March 3, 2011
Question: Heating and holding our ingredients
This is a good question because the last thing we want is to have rancid oils in our products (click here for more information on the mechanisms of rancidity)!
Given how many things we use call for inclusion in the cool down phase - extracts, panthenol, silicones, some cationic polymers, and so on - you'd think that we'd want to treat our oils more gently. Heating them up to 70˚C and holding can't be a good thing, right? But heat won't ruin our lovely oils because we aren't heating them up to a temperature where they will start smoking or burning or oxidizing. (For instance, coconut oil has a smoke point of 180˚C or 350˚F. Click here for a list of the smoke points of various oils.) As you can see, the more refined the oil, the higher the smoke point. Grapeseed oil isn't as fragile as one might think: It has a smoke point of 216˚C, which is right in the middle of the list!
Yes, heat will increase the rate of oxidation of our oils, but only by a bit, and we can compensate for that by including Vitamin E or another anti-oxidant. It's not going to speed up the rate of rancidity so much that a 1 year shelf life lotion becomes a three month shelf life lotion. It's more like making a 1 year shelf life lotion a 11.5 month shelf life lotion. And besides, if you don't heat and hold, you're not going to get a great emulsification anyway, which severely limits the shelf life of every product to "the moment it fails", which could be shortly after creation.
Someone else asked about including our lovely hydrosols, aloe vera, and other botanicals in the water phase, reasoning that the goodness will be boiled out of them. But we aren't boiling our lovely ingredients! 70˚C or 158˚F isn't as close to the boiling point as we think, and the molecules in our ingredients can stand up to the heat without falling apart easily.
This is why knowing the phase into which we put our ingredients is so important. We don't want to add a cool down phase ingredient into the heated phase as this could hurt the great properties for which we're using it!