What preservative should I use? How much of it should I add?

If you are making something that contains water, you need a broad spectrum preservative. Imagine a tub of soup left out on your kitchen counter; how long would it have to sit there before you wouldn’t want to eat it anymore or serve it to company? That’s the kind of timeline we’re looking at for bacteria setting up shop in your watery concoctions.

There are a lot of broad spectrum preservatives readily available from DIY suppliers. Here’s a few:

  • Germall® Plus (powder or liquid)
  • Optiphen™
  • Optiphen™ Plus
  • Phenonip®
  • Leucidal® Liquid (not truly broad spectrum, but also not an antioxidant)
  • NeoDefend™
  • NataPres™
  • Gluconolactone & Sodium Benzoate

These things are often sold in the “preservatives” section but are not preservatives—just antioxidants. They are usually far less scary/more natural sounding, but they will not do the job at all.

  • Sodium lactate
  • Grapefruit seed extract
  • Rosemary antioxidant
  • Vitamin E

I encourage you to do your own research and decide for yourself which preservative will work best for you. I also encourage you to read everything about the preservative from the supplier to determine if it will work for you. Effective pH range and solubility are important things to consider. I’ve compiled a table of information about different preservatives here, complete with sources so you can read and learn more.

So, with all that in mind, for relatively foolproof preserving, I usually use Liquid Germall Plus. It is water soluble, effective in small amounts, and has a broad effective pH range (3–8). It’s not easily accidentally deactivated. You are unlikely to need to test the pH or adjust it. It has a usage rate of 0.1–0.5%, though I would recommend erring on the 0.5% of things for home use, since our kitchens are far from sterile.

The two active ingredients (Diazolidinyl Urea [and] Iodopropynyl Butylcarbamate) are a bit scary when you research them, but Liquid Germall Plus is 60% propylene glycol, meaning only 40% of your preservative is the scarier stuff, which means, at a 0.5% usage rate, only 0.2% of your formula will be “scary” ingredients. With the tiny inclusion of those scary ingredients, the rest of your formula will be protected from other scary things, like fungus and mould. In a 100g batch of lotion, that translates to 0.2g, which is barely anything, especially when spaced out over many uses.

Please see my Resources page for a list of links to places to purchase ingredients including preservatives.

How much do I need to use?

Each preservative will have a different recommend usage rate, which you can get from your supplier.

I made a handy-dandy preservative calculator that you can use here. Or, for the math:

Let’s say your preservative should be used at 1%; if your recipe contains 100g of ingredients, that’s approximately 1g of preservative. That’s not 100% accurate as 1% of 101g (original recipe + weight of the preservative) will be just over 1g, but with the small batches we’re working in the the accuracy level of the scales we’ve got at home, I consider it to be close enough.

  1. Figure out how much your recipe weighs. Either add up the weights of all the ingredients or weigh the final product.
  2. Figure out the recommended usage rate of the specific preservative you are using. Your supplier will provide this. Choose the higher end of the range since we’re not manufacturing in sterile labs.
  3. Multiply the weight of your product by the usage rate percentage, and divide that number by 100. So, if your concoction weighs 50g and the usage rate is 2.5%, that would be 50 × 2.5 = 125. 125 ÷ 100 = 1.25. That means you should add 1.25g preservative to your concoction.

Posted in: Preservatives