Glycerine, Glycerites and Preservative Power
Lise
Several of you have asked me about the preservative power of glycerine.
Can glycerine really function as a stand-alone preservative in a glycerite?
This is an excellent question.
I do wish the answer was more straightforward though.
The answer is "yes, but it depends."
Depends on What?
The need for adding preservative to a glycerite not only depends on the raw materials, but also how much you use of each component.
You: (groan) Really, Lise? Seriously? Does this have to be so difficult from the get-go?! Surely there is a simple answer!
I feel your frustration.
But you have to remember that glycerites can be made with a gazillion (if not a trillion gazillion) different things:
dried herbs
fresh herbs
dried whole flowers or petals
fresh flowers or petals
dried fruits
fresh fruits
fresh veggies
So there's really not an easy answer to this question. I wish there was, but then life would just be far too simple, and life – apparently – doesn't like being simple when it comes to glycerites.
Why Life Isn't Simple When it Comes to Glycerites
During my research of glycerite-making methods, I have come across numerous different recommendations of how much glycerine to use to ensure proper preservation of the end product.
During all this time, I have never come across a single written (or online) source that could recommend percentages for a fresh food glycerite.
Not. A. Single. One.
I did keep notes of the recommendations I did find, which mostly focused on using reconstituted dried herbs. According to those, each of the following percentages is 'the norm' for how much glycerine to add to a glycerite to ensure proper preservation:
over 25%
50%
minimum 50%
over 55%
75%
80%
Quite a span, there, don't you agree?
Many of these sources also recommend a 'use by' period which ranges from 6-24 months.
Every one of the above mentioned sources have struck me as serious, professional, and experienced (some links below). As glycerites have roots in herbalism, many were referring to extracts meant for consumption.
The Difference between Glycerites for Consumption and for Cosmetics
A glycerite for consumption is generally stored in one place at a steady temperature until it is added directly to food/drink and consumed.
On the other hand, a glycerite for cosmetic use may find itself in any kind of temperature and humidity (bathroom, handbag, pocket etc) in the end product. It is also opened and dipped into numerous times (with a possibility of contamination from the user) and still expected to have a shelf life that surpasses anything meant for consumption.
How Much Preservative?
My very first post on glycerites was a cucumber extract (link to updated post) which included the addition of 0.5% preservative.
That amount was inspired from a glycerite making guide on cosmetic supplier Aroma Zone's website which calls for 50% glycerine, reconstituted dried herbs and the addition of 0.6% broad spectrum preservative. (LINK)
For the cucumber glycerite, I chose to use 0.5% preservative and a glycerine percentage of 'just around 50%'.
'Just around 50%'? Is That Accurate Enough?
Nope.
'Just around 50%' is not accurate enough.
With fresh fruit and veg, the water-to-glycerine ratio gets tricky. To add to the 'fun', fruits (and many vegetables) contain sugars which can be an additional challenge.
If you don't know the exact water (and sugar) content, it's pretty much impossible to calculate exact percentages of anything.
How does one measure the exact water (and sugar) content of a fresh strawberry?
One cannot (if one also wishes to use it in a glycerite).
The only way to approach the water question is to find the average water content of said fruit (or veg), then work from there.
But average numbers are not exact numbers.
So.
To know for absolute sure how much – if any – preservative needs to be added to your glycerite, you need to do some calculating – followed by a bit of testing.
For Real?!!
You: (groaning and eye rolling) Math and then testing, Lise?! Seriously?! Could this get any worse? Why isn't there an easier way?
I totally feel your pain.
Really.
I've already spent quite a bit of time trying to find the answers. And if there was an easy, all-in-one, simple-dimple answer to this question, I would hand it to you on a silver platter.
But there isn't, so I can't.
But there's something I can (and will) do – provide you with a general guideline, and that is this:
Glycerine will greatly reduce the possibility for bacterial growth when it exceeds 50% percent of the solution.
You still have to do the calculating on the material you are using and go from there.
From what I have been able to find in the time I have been working with glycerites, the information on the preservation power of glycerine in glycerites for cosmetics is pretty much uncharted territory.
In my book The Art of Making Glycerites for Cosmetics, there are guidelines to help you do the calculation, but they are still guidelines. If I had tested every possible raw material on the planet, I could have given you a chart with set percentages, but that would probably take me longer to get through than anyone has the patience to wait for (even me).
I'll conclude with a few updated helpful tips to help you on your glycerite-making way.
LisaLise's Glycerite Making Tips
Measure every ingredient accurately – and only by weight
Work clean (keep your work space clean, sanitise equipment etc)
Use prime raw materials (discard anything that isn't fresh or perfect)
Keep copious notes
Label everything you make (date, ingredients, and everything else that will help you recreate – or be able to pinpoint why you don't want to recreate – your formula
Save a LABELLED, DATED portion of your formula for observation – even long past your 'use by' date. This is by far one of the most educational things you can do for yourself, and will require a bit of storage space as you continue to make glycerites.
Finally, don't forget to have fun with it – even the math part.
You can totally do this.
How do I know?
Cuz I just know.
Do Tell
How long do your glycerites last? Please share in a comment below!
References
John Kabara, Donald S Orth, Preservative free and self preserving cosmetics and drugs, Priciple and Practice, 1996, 45-69 (LINK)
Preserving Syrups, The Pharmaceutic and Compunding Laboratory, UNC Eshelman School of Pharmacy (LINK)
Cech, Richo, Making Plant Medicine, 2000 (LINK)
Gladstar, Rosemary, Medicinal Herbs: A beginners Guide, Lemon Balm Glycerite, 160 (LINK)
Gladstar, Rosemary, Family Herbal Guide to living life with energy, health and vitality, 2001 (LINK)
Green, James, The Herbal Medicine Maker's Handbook - A Home Manual, p 185-192 (LINK)
Wynn, Susan, Fougere, Barbara, Veterinary Herbal Medicine, p225 (LINK)
Fetro, Charles W, Avila, Juan R, The Complete Guide to Herbal Medicine, p8 (LINK)
Preservative for Biological Specimens , US Patent, 1978 (LINK)
