Sunday, June 3, 2012
Question: How do you figure shelf life?
I did address this concept this time last year, but this is one of those topics that it can't hurt to revisit regularly! The links below can be found in the FAQ, which is now located in the "links to lists" section on the right hand side of this page.
In this post, joesoap asks: Hi, love your blog and recipes, thank you! I'm lookng to make a room spray, but am unsure of how to work out the shelf life - can you help - if we took your recipe as an example?
The quickest and easiest way to figure out the life span of a product is to consider the life span of the product with the shortest shelf life. If you have something like grapeseed oil in your lotion, that'll be the shortest life spanned product and you can consider the product to be good for three months or so. (If you opened the bottle three months ago, then the life span of that product might only be a couple of weeks, which is why I never recommend using something like grapeseed oil.) If you use something like mango butter as your primary oil, you could have a shelf life of up to two years. The oils in your product will tend to be the ones that determine the shelf life of a product.
An aside...The shelf life of your oil is determined by the number of double bonds in the fatty acids. Something like stearic acid that has no double bonds will take much longer to go rancid than something like olive oil that contains a lot of oleic acid with one double bond. And something with linoleic acid, which has two double bonds, will go rancid faster than something like olive oil. This is why coconut oil - filled with the unsaturated fatty acids lauric, myristic, and palmitic - can last for up to two years, and why grapeseed oil, which is almost all oleic and linoleic acids with not a lot of Vitamin E, lasts only three months. If you want to learn more, click here and start at the beginning of the series on the chemistry of oils.
How do you find out the life span of an ingredient? Ask your supplier! If we use polysorbate 20 as an example, From Nature With Love notes it has a two year life span.
If your supplier doesn't know, then make the assumption that whatever ingredient you have will last six months and you won't go wrong, although most of our ingredients are good for at least a year. Most of our powdered extracts, hydrosols, and liquid ingredients are good for a year. Our oils will vary. For instance, if I were to take one of my lotion recipes and consider the ingredients - say, this lotion for dry skin - we would consider the oils to have the shortest shelf life. Wheat germ oil has a life span of six months, while rice bran oil has a life span of 1 year. Add an anti-oxidant and you'll get a bit more time out of this lotion, but it's hard to figure out exactly how much, so assume it's the amount for the oil and make a note to use it by that date.
As a note, even if you manage to make a lotion with a two year life span - using esters and/or butters - consider the life span of your preservative. Liquid Germall Plus has a life span of two years, which is fairly typical of preservatives.
polysorbate 20, 1% fragrance oil, 0.5% liquid Germall Plus, and water to 100% - and note that polysorbate 20 and liquid Germall Plus are good for two years, then the shortest lived ingredient would be the fragrance oil. (Fragrance oils generally have a life span of a year, but some will have a life span of two years. Check with your supplier.) I'll call the life span on this product a year.
Look at your favourite recipe and figure out the life span to get some practice doing this!
As an aside, when I see these Extreme Couponers or Doomsday Preppers buying enough body wash or shampoo to last forty years, I cringe because they'll be washing with some really gross products in as little as three years from now!
An aside: Shelf life of products (part 1)
An aside: Shelf life of products (part 2)
Emollients - oils, butters, and esters!
Determining the shelf life of your lotion
How do anti-oxidants affect the shelf life of your product?