How to preserve hydrosols

About a year ago I wrote this blog post:

Are you buying contaminated hydrosols?

to answer hundreds of questions that we've received from skincare formulation students and our readers. It brought an avalanche of comments and questions and afterwards I have received many questions from artisanal manufacturers who make their own hydrosols and ask for recommendations for preserving their homemade hydrosols.

Before I directly go to the question, I would like to recap the old blog post and explain why we emphasize on purchasing preserved hydrosols.

Read my other blog post before proceeding:

How to spot fake hydrosols

Disclaimer: This post is about preserving your homemade hydrosols (the product of steam distillation of dried or fresh plant material in a cupper, stainless steel or glass still). It doesn't cover the preservation of infusions concoctions and extracts.

Unpreserved hydrosols

In an industrial scale, most hydrosols are unpreserved. The hydrosol is quite hot when it condenses and is pretty much sterile and free of contamination. Contamination happens during transport and storage. In the manufacturing site, the hydrosols are filled in disinfected drums with almost no oxygen/air in the headspace (they may even fill the headspace with nitrogen gas). These unpreserved drums have a shelflife of about 6 months (as long as the drum is not open).

Photo: Courtesy of Wendy Gardner from Glow Skincare: www.glow-skincare.com/

In large scale manufacturing plants they open the drums and empty the whole content into the mixer for a single batch and preserve the finished product and everybody is happy.

The main problem rises when you purchase unpreserved hydrosols from retailers. They usually open the drum and refill the content into smaller bottlers (which are hopefully clean but neither disinfected nor sterile) and send the hydrosol to you, mention a shelflife of 6-12 months for the content and recommend a storage in the fridge. These refills are most often already contaminated as you receive them and no matter how you store them, there is no way to keep them free of contamination.

Post-adding a preservative to an already contaminated hydrosol is no solution.

You can only discard the hydrosol and drop some tears for your wasted time and money.

What to do with your homemade hydrosols?

This is one of the most frequently asked questions in our mail box. Hundreds of our customers and readers make their own hydrosols and are concerned about the microbial stability of their precious hydrosols and seek our advice for a suitable preservative.

Do you need a preservative for your home-distilled hydrosols?

This is rather a hard question to answer and as always, there is no "one-fits-all" solution. I have some tips to start with based on our experience and the feed back from our readers and customers but I strictly recommend that you run your own experiments and find out what works for you.

• keep in mind that the hydrosols distilled in a cupper still have a slightly better microbial resistance compared to glass and stainless steel. This is mainly because of low amounts of cupper ion found as residue in the hydrosol which acts as a preservative

• if you're distilling in small quantities, filling your hydrosols in disinfected or sterile bottles and use the whole content within a few days in a finished product that you're going to preserve, then you don't necessarily need to preserve the hydrosol. Keep the closed bottle in the fridge till you use it.

Read my previous post: Sterilization or Disinfection? This is the Question before you proceed

• if you're distilling in quantities that you're not going to use within a few days then you'll need to preserve your hydrosol.

Photo: Courtesy of Wendy Gardner from Glow Skincare: www.glow-skincare.com/

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What you need to consider for choosing the preservative

The most important factors in this case are:

• solubility: you need a water soluble preservative or preservative blend
• pH: the pH tolerance and performance of the preservative
• Compatibility with other ingredients and other preservatives in your final formulation
• legislative stuff and max. dosage: most components of "natural" preservatives are subjected to a max. dosage in different skincare products (sorbic acid and its salts, benzoic acid and its salts etc.). This means, when you use these components to preserve a hydrosol, the concentration of that certain component should be considered when you're preserving the finished product (don't hate me for making this so complicated)

Read our previous blog post

How to protect your "natural" preservatives from deactivation

before proceeding.

Preserving a hydrosol is different than preserving a finished product

When you preserve your hydrosols and then use them in a formulation, you still need to preserve the finished product. Preservative demands are quite different for a hydrosol and a finished product.

A preservative system that is fully sufficient for the hydrosol is not enough for a finished formulation.

Which preservatives you can use for your hydrosols?

Freshly distilled hydrosols have a pH between 4,5-5,0. The pH is slightly lower for hydrosols from a cupper still compared to glass and stainless steel. This pH is not low enough for a self-preserving status. This means, your hydrosol needs a preservative if you're going to store it for more than a few days.

Considering the pH, you can not use most water soluble preservatives (organic weak acids with a pH-dependent performance such as benzoic acid, p-anisic acid etc.) without a pH adjustment.

@SkinChakra we offer water soluble preservatives which could be used to preserve your hydrosols:

Preservative 1388 eco and Versatile BL are among these preservatives. In my opinion however, it would be over-preserving if you use these preservatives. Apart from that, you'll need fiddling with pH when working with these preservatives. It means, you need to increase the pH of the hydrosol before adding the preservative.

During all my years of experience with commercial manufacturers of hydrosols I've seen two options which are affordable and easy to perform for artisanal distillers:

1- Citric acid

citric acid is a food preservative and is completely acceptable in "natural" hair and skin care formulations. We usually use it to adjust the pH of finished formulations. In skincare formulations it is not considered a preservative. However, because of its chelating properties, it can boost the preservative performance.

Many commercial hydrosols use 0,1% citric acid as a preservative. As always, you need to test the efficacy in your system.

2- Citric acid + potassium sorbate

Potassium sorbate is a common component of many commercial preservative blends and it is very often used (in combination) to preserve raw material as well as finished products. Sorbic acid and potassium sorbate are no stand-alone preservatives and have only anti-fungal properties. There is a max. dosage (0,5% sorbic acid) in finished products in the EU. Keep this in mind when you're using sorbic acid or potassium sorbate to preserve your hydrosol (in case your other raw material contains potassium sorbate or sorbic acid or you have them in your final preservative system)

Keep in mind that potassium sorbate and sorbic acid are sensitive to oxidation and UV light and you need to keep your hydrosols in light protected containers.

The dosage that our own supplier of hydrosols uses for preserving hydrosol is:

0,15% potassium sorbate + 0,05% citric acid

(you need to test the efficacy of this blend in your system)

Using preserved hydrosols in finished formulations

I've seen many formulators that use preserved hydrosols (single or a combination) as a skin toner without any modification. Keep in mind that:

1- the pH of the hydrosol blend is usually too low for a skincare product. This pH, in a daily use may cause skin sensitization and irritation. When you increase the pH of the hydrosol blend to make it safe for everyday use, you need to preserve the blend according to the pH of the system.

2- As soon as you add any ingredient to your hydrosol and fill it in a bottle or jar that is being opened hundreds of times during the shelflife, the simple preservative used for the hydrosol is not sufficient enough for the system and you need to preserve your blend with a broad-spectrum preservative system.

Preserving raw material and the finished product are among the most challenging tasks of a formulator. The more "natural" and plant based ingredients in a formulation, the more challenging the task. Keep testing and experimenting to guarantee the safety and integrity of your products and to avoid over-dosing. Remember the golden rule:

As little as possible

As much as needed

BeHappy and have Fun