Wednesday, January 25, 2012
Heating, holding, freezing, and thawing our ingredients!
If we heat carrier oils, will they go rancid quicker? Are we destroying the goodness in them?
I answered this question last year in this post, but let's summarize it here. (Quick answers are no and no.)
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.
Can we heat delicate oils - like evening primrose, borage, squalane, and so on - in the heat and hold phase of our products or should we leave them for the cool down phase?
There is no chemical difference between what we call exotic oils and carrier oils. They both contain fatty acids, phytosterols, polyphenols, and all kinds of vitamins and minerals. The concept of one oil being a carrier oil and another being an exotic oil has no basis in chemistry - it's a designation we've given the oils based on availability and cost. Wheat germ oil might or might not be an exotic oil depending upon the section of the store your supplier puts it in and how common it might be in your part of the world. Don't get me wrong...there are differences between something like borage oil and sunflower oil (for instance) - borage feels drier, it contains GLA, it has a different fatty acid make up - but they aren't so different that we have to treat borage with great delicacy and sunflower oil with reckless abandon!
I've only seen one oil listed as needing to be in the cool down phase and that's kukui nut oil. And to be honest, I'm not seeing anything scientific showing that kukui nut oil can't be used in the heated oil phase of the product or anything about its sensitivity to temperature. I got this information from a supplier's website, and I can't promise you that it's accurate.
Every carrier or exotic oil we use should go into the heated oil phase to ensure it emulsifies into the product. If you put them in the cool down phase, you are risking an epic lotion failure, which is doubleplusungood and to be avoided! There is no need to put our exotic oils into the cool down phase because we aren't heating them up to the point of smoking, which is really the only way we can damage them.
70˚C or 158˚F is not that high a temperature in the grand scheme of things. Vitamins can handle high temperatures - click here for information on Vitamin C, for instance - as can our fatty acids, polyphenols, phytosterols. In this study, phytosterols were heated for either 50˚C for several weeks or 100˚C for an hour, and the oils "did not show any significant variation in the phytosterol content."
Tara asked in this post: Is there some validity in the point that it is the CHANGES in temperatures that help to destroy our oils? I like to freeze most of my oils, but they need to be brought to room temperature before I can use them. I then refreeze them and thaw them again the next time I use them. Is this more destructive than if I just leave them at room temperature (or slightly below, as my work area is in the basement)?
It's a good question, and yes, there can be some changes in ingredients when they go from being frozen to heated, but there doesn't seem to be so big a difference when it comes to oils, butters, and exotic oils. The changes of concern are when we have to worry about ice crystals ruining something - say veggies or meat - or when we have a lotion that goes from being in my freezing car after a week of snow days into my too warm office. I regularly freeze and thaw my oils without problem.
So can you freeze and thaw then re-freeze your oils? Yes. It's fine. Can you leave your oils at room temperature? Sure. There's no problem there either!
I know the plural of anecdote is not data and I can't just ask you to take my word for the idea that you can freeze and thaw oils without problem, but I can't find any good studies showing that it's okay to do this. You can see what the North Dakota State University has to say about freezing oils (very brief, scroll down a bit). The key problem with freezing anything is the creation of ice crystals by the water in the product. Oils and butters don't contain water, so there's no problem there!
If we can freeze our oils and butters, can we freeze our anhydrous products? In theory, yes. It would depend what product you're freezing. If you want to freeze a bath oil - sure, go ahead. Bath melts? Why not? Your sugar scrub base (without sugar)? Sure! A balm or lotion bar? Why not? And so on. And don't worry about the bottles - when oil freezes it contracts, unlike water, which expands! (Click here for more on water and freezing!)
You cannot freeze products that contain water! Emulsified products are especially fragile when it comes to freezing as are products that might contain water soluble ingredients (like conditioner bars that might have hydrolyzed proteins and panthenol, for instance).
Learn more about oils, butters, exotic oils, and esters in the emollients section of the blog!