Tuesday Wonderings: On recipes that don't total 100%, Karen writes, I have been reading the blog for a while, and for some reason I understood that certain ingredients were to be used ABOVE the 100%. Such as everything will add up to 100% and THEN we add the 1% (of that total) of fragrance and the 1% preservative equaling 102%.
Anyway, I wondered, if a preservative's recommended usage is .5-1% how do we decide how much to use? Should we always use the maximum amount allowed?
All ingredients should be part of the 100% total of the recipe because, as they mention in the Simpsons, 100% is the most you can have. 100% means 100% - it means the total of everything, and that's what we strive to have in our recipes.
Let's say we have a recipe that looks like this...
SIX INGREDIENT LOTION WITH SHEA, SOY BEAN, AND SESAME OIL (from the six ingredient challenge post)
HEATED WATER PHASE
20% aloe vera
HEATED OIL PHASE
10% refined shea butter
10% soy bean oil
10% sesame oil
COOL DOWN PHASE
0.5% liquid Germall Plus
And you want to add a fragrance or essential oil at 1%, you would have to remove something from the recipe to keep it at 100%. So I might remove 1% water or 1% aloe vera or 1% glycerin. We don't tend to remove from the oil phase as it could mess up the emulsification, so the water phase is where we eliminate things to keep the recipe at 100%.
So you'd add 1% essential or fragrance oil to the cool down phase and remove 1% from the water phase, leaving us with 39.5% water.
Let's say we have a different preservative, something like Geogard Ultra, and you want to use it at the maximum 2%, you would have to figure out the difference between that amount and the amount of preservative I use - 0.5% - leaving us with 1.5% difference. Now remove that 1.5% from the water amount, leaving you with 39% water and 2% Geogard Ultra.
Calculating percentages in lotions
How to convert recipes from percentages to weights
What happens if our recipe totals more than 100%?
Learning to formulate: A note about percentages
Learning to formulate: The water phase
How to figure out how much preservative to use? Take a look at the suggested usage rates for something like Liquid Germall Plus. They suggest 0.1% to 0.5% in the cool down phase. We don't want to use more preservative than necessary, but I generally tend to use the maximum for a number of reasons. The first is that I can't be completely sterile in my workshop. As clean as I might try to get it, there might still be things lurking on my freshly washed forks or Pyrex jugs. The second is that I don't know what might happen after I give the product to someone. I like to think my friends and family follow the rules I set out - don't put wet hands into a sugar scrub - but I can't guarantee it. By using the maximum allowable preservative level, I make sure that I chase off those beasties as well as I can.
When you think about it, the maximum level is still pretty low. If you want to use the minimum level of preservatives, have at it. In either case, monitor your products the first time you make them to see if they work well with your chosen preservative level.
So the answer to the question - should we always use the maximum level? Not necessarily. I like to use the maximum level because it's what I feel works best for the products I make. If you want to use less, use less, but monitor the products to make sure they remain well preserved.
As an aside, I have had one product go off on me in all my years of crafting, and that was one with Advanced Aloe Leuicidal and it might have been because it was strongly anionic.
When choosing your preservative, consider the product as a whole. When I have made something that might be harder to preserve - something with loads of botanicals, like my toners - I go for Germaben II at the 0.5% to 1% usage rate because it's billed as working well with hard to preserve ingredients. If I'm making something oil soluble, I need an oil soluble preservative like Phenonip or Liquipar Oil.