Tuesday, August 5, 2014

Rancidity in our products: The shelf life of our oils and anhydrous products

Why did I say yesterday that we don't encounter rancidity as much as we encounter other things like contamination? Because we really shouldn't be making batches so large that they outlive the shelf life of the product. So let's say you want to make this manicure balm, how long is the shelf life?

26% lanolin
12% lecithin
12% hazelnut or soy bean oil
37% mango or green tea butter
12% beeswax
1% fragrance or essential oil

The ingredient with the shortest shelf life is the soy bean oil or hazelnut oil, both of which have shelf lives of up to a year. So let's say you make 100 grams of this cuticle balm, will you have it longer than a year? Probably not. If you make 200 grams or 300 grams? Probably not, if you use it every day. The problem comes when we are selling our products or giving them away to friends. Quite often people will put these things away or cherish them as handmade, so they aren't used. By adding an anti-oxidant, we ensure that when they find this balm in six months or even a year, the horrible stench of rancidity doesn't come wafting from the container.

How do you figure out the shelf life of your products? It's the shelf life of the ingredient with the shortest shelf life. So if you were to use grapeseed oil in this product, it'd have a shelf life of about 3 months as that's the shelf life of that oil. If you were to use evening primrose oil, it'd have a shelf life of about 6 months.

Related posts:
Determining shelf lives of products (part 1)
Determining the shelf life of your lotion! 
How do anti-oxidants affect the shelf life of your product?

Now, remember that the shelf life of the oil starts when it's exposed to air. If we're using a reputable supplier for our oils, you can consider that the day the bottle arrives on your door step. Write the date you received it on the bottle and store in a cool dark place. Heck, store it in the fridge or freezer to stretch that date further. (In the freezer, consider the process stopped. Yes, you can freeze your oils!)

So if you bought olive oil on June 1st, 2014, it would have a shelf life until June 1st, 2015, if stored in the cool dark place. If you put it in the freezer, every day is June 1st, 2014, so you'd consider it as one year from the date you take it from the freezer. If you use that olive oil in a product, and it is the ingredient with the shortest shelf life, you could consider the shelf life of that product to be one year from the date of making.

This is one of the reasons I don't use grapeseed oil at all. It has one of the shortest shelf lives of all our ingredients - three months - and that time can fly by so quickly. All it takes is a weekend or two with a cold that prevents you from getting into the workshop, and you've got eight weeks of use out of that bottle! 

We should be using anti-oxidants in our products because rancidity is a process, and the longer we can stretch out the day of stenchiness, the better. Rancidity isn't the same as contamination, so using a preservative will not help with contamination, we need to use an anti-oxidant. (And using an anti-oxidant won't help with contamination...) As I mentioned yesterday in my summary about rancidity, I would recommend oil soluble anti-oxidants like Vitamin E over water soluble ones like citric acid because they are less likely to mess with the chemistry of our products.

Join me tomorrow for more fun formulating!


Clive said...

I wish vitamin E wasn't so expensive!

Diva Soap said...

And what about vitamine E shelf life? Can it go rancid?