Saturday, March 23, 2013

Weekend wonderings: Preserving fresh fruit in products, measuring pH in a conditioner, and determining if an old oil is bad

In this post about honeysuckle extract, Monique asks: Can you use this to preserve fresh puree fruits in sugar scrubs?

No. You can't use this type of powdered honeysuckle extract as a preservative. There is a type of honeysuckle extract that you might be able to use as a preservative, as we see in Natrapres preservative, but it isn't a broad spectrum preservative and it isn't suitable for preserving anhydrous products like sugar scrubs. (And I haven't really seen good results from anyone using it, to be honest.)

But which preservative to choose to preserve fresh fruit puree in a product is the least of our problems. You really shouldn't be adding anything with water to an anhydrous sugar scrub because any water soluble ingredients you add will dissolve the sugar and make a horrible mess in a jar. Secondly, you really shouldn't be using fruit puree in any product because the potential for contamination becomes almost a guarantee if you are keeping it for more than one application, especially if you're mixing that fruit puree with sugar!

Consider this: Mash a banana, mix it with some sugar, and leave it on the counter for a day. Watch what happens over those 24 hours. What happens after 48 hours? Fresh fruit puree may sound lovely in theory, but it starts to sound quite icky after even a day out of the fridge as it browns, gets mushier, and starts the rotting process. Which is one of the reasons powdered and liquid extracts exist. We want to have those lovely sounding fruits, veggies, flowers, and leaves in our products, but using the extracts means we get quality control for things like the amount of active ingredient, good preservation, and good solubility, things we don't get adding a mango to a lotion!

Related posts:
Answering comments: Salt or sugar in water based scrubs
Question: How does Lush use fresh fruit in their products? (part one)
Question: How does Lush use fresh fruit in their products? (part two)
Why can't we use tea in our products?

In this post on how to measure pH, Mya asks: I make my own conditioner. I have a pH meter that I bought from the Herbarie. Why is it that when I measure the pH of my product right after the emulsification process (after I am finished making it), the pH is lower than it is the next day? Usually, when I measure the pH the next day it is 0.20 to 0.50 higher. Do you know why this happens?

It is likely because your product is warm when you measure it, and it really should be at room temperature. The solubility of some of our ingredients rely upon room temperature or close to room temperature (20˚C to 25˚C), so a warm product isn't really the true measure of what it will become. Let it sit until it is at 20˚C to 25˚C before measuring it.

As a quick aside, it isn't a wise idea to stick your pH meter into your product the way I'm showing you above due to potential contamination of your entire product. I take pictures like this because it looks cool for the blog and it demonstrates my point. In the picture above, the red stuff is my pH 4 buffer. But I recommend you put a small sample of your product in a cup and measure it that way, then dispose of it. It's not that our meters are contaminated, but they might be and the fewer chances for contamination we have, the better.

Related posts:
Chemistry Thursday: How to test pH?

Chemistry of our skin: pH of our skin
Chemistry of our skin: pH and skin care products
An aside: pH of lotions
Adjusting the pH of our products

In this post on hemp seed oil, Nina asks: How you can tell when oil is bad? I have a bunch of oils that I bought three years ago - can I still use them for lotions? If not lotions, how about soap making? And, are they potentially dangerous to use if they are old? For what it's worth, they smell fine. Thanks!

Normally we can tell an oil is bad by the smell! But rancidity starts the day the oil is created, but we don't really notice the stench until it reaches critical mass and we have to throw that bottle out right that moment!

Every oil has a shelf life. Some can be up to a year - like soy bean or olive oil - and others are almost measured in weeks - like hempseed or grapeseed oil. There really aren't any natural oils that can go longer than a year, so I would be really apprehensive about using an oil that hasn't been in the freezer three years later. It might be that today they smell okay, but tomorrow they are horrible and you've wasted a lot of supplies creating a horrible product. (And when you heat them to make the product, you'll be speeding that rancidity up by just a litlte bit!) They aren't dangerous - they just smell really awful, and you wouldn't want that on your skin!

As for soap making, I don't make soap, so I can't comment, but I would think that an oil that isn't suitable for lotions would be a bad idea for soap as well.

So the short answer is that I wouldn't chance it. But it's really up to you to make that decision.

Related posts:
Rancidity: A primer
Mechanisms of rancidity

Have a question you want answered? Click here for the Weekend Wonderings comment post and let me know! You can leave questions anywhere on the blog, but I check there first every week!


Monique said...

Beautiful! Thank you

Anonymous said...

If a rancid oil can be used in soapmaking? Absolutely, according to the book Scientific Soapmaking by Kevin Dunn this "is the decomposition of the oil molecule into glycerol and free fatty acid (not part of a triglyceride, in essence the oil has already saponified to some extend. An oil with a high free fatty acid concentration if often deemed rancid, though it is not necessarily unfit for soapmaking.The main effect of free fatty acids on soapmaking is that the oil reaches trace very quickly".
I am a soapmaker and I tried it with my rancid oil. True. Barely had time to pour into the molds and the end result was well just soap,no funny smell or anything. Last but not least he says "Note that if an oil contains free fatty acid, there need not be anything wrong with the soap produced from it. Though the free fatty acid reacts quickly with lye, the product of this reaction is just soap".
I hope this answers your question.


Corina said...

I have just started to make soaps and have read that rancid oil can cause DOS - dreaded orange spot- which can migrate to other soaps nearby as they are curing. I would pitch the old oil, and buy new.