Monday, April 5, 2010

The argument for heating & holding lotions

One of the biggest disputes I see in lotion making is the debate over heating and holding our ingredients before mixing the oil and water phases together. I can give you several good reasons to join the heat and hold camp if you still think it unnecessary!

Click here to see the basic lotion making instructions post.

Whenever I make a lotion, I weigh out the heated water phase and the heated oil phase separately, and put each into my double boiler. I heat each until they reach 70˚C, then hold it there for 20 minutes. Why do we do this? The first is to eliminate any possible contamination by heating it, and the second is about the critical micelle concentration, which requires that both phases are the same temperature when we add them together. And finally, we need the phase inversion to create a stable emulsion.

Okay, so the contamination stuff is obvious. If we are using water with icky things in them, a prolonged period of heating and holding will help kill the nasties!

The critical micelle concentration is a little more complicated. When we reach the critical micelle temperature or Krafft temperature - suggested as 70˚C to 80˚C for Polawax - we will see our micelles form properly, which means the emulsification has worked and we will get a nice lotion that shouldn't separate. If our oil phase is at 70˚C and our water phase is at 100˚C (boiling point of water in Celsius), then they may not come together properly. If our oil phase is lower than 70˚C, we might see a very unstable emulsion.

We know that when we heat something we increase its solubility. Non-ionic emulsifiers (like Polawax and e-wax NF) are water soluble at low temperatures and oil soluble at higher temperatures. At the lower temperatures, the Polawax forms an oil-in-water emulsion. At the higher temperatures, the Polawax forms a water-in-oil emulsion. So shouldn't we do it at lower temperatures so the Polawax will create what we want - an oil-in-water emulsion?

Creating a water-in-oil emulsion that will eventually turn into an oil-in-water emulsion is a concept called phase inversion. We need to reach the phase inversion temperature to make this process work. (Click the link to read more about this...)

So if you are boiling your water and heating your oils in a microwave, odds are pretty good that you don't have both phases at the same temperature and you won't see the phase inversion. You will get an emulsion, but it won't be as stable as the one achieved with the phase inversion method.

Point of interest: Here's a post about all the different ways lotions can go wrong, most of which have to do with a failure to get the ingredients to the proper temperature.

To summarize: If we heat and hold our ingredients at 70˚C for 20 minutes, we are assured that our emulsifier will be very oil soluble, which means it will create a water-in-oil emulsion that will eventually become an oil-in-water emulsion, which is very stable. We are assured our micelles will be a nice size, and we have eliminated most of the nasty contaminants that could ruin our lotion. In short, by heating and holding, we are ensuring we have a stable lotion that will remain emulsified and bug-free for a very long time!

21 comments:

Lalla said...

Do you know what type of emulsifiers ( beside the non ionic) can produce a phase inversion? I mostly use anionic and cationic emulsifiers ( none of them are ethoxylated)and I've always poured the water phase in the oil phase without being sure there is a phase inversion.

Meaue said...

This answers many of my questions as to why some of my creams/lotions have separated. Thanks!

Susan Barclay-Nichols said...

My understanding is that only ethoxylated emulsifiers go through the phase inversion process, so if you're using something like BTMS-50 or an un-ethoxylated emulsifier you aren't experiencing this.

Having said this, the chemistry behind phase inversion is pretty deep and I haven't studied all of it, so I could be wrong...

Nedeia said...

What could go wrong if you heat your ingredients at more than 70 degrees, say 80? I do not have a crock pot , and the best way I have found to get the 2 phases at the right temp at the same time, is to place them into a bowl of hot water. they get to 70 degrees or a bit more, but I cannt hold at 70 for 20 minutes, the water will cool down eventually, and constantly heating it from time to time is not an option for someone that also needs to watch a kid :)

Using a 0.5-1% Optiphen would keep the lotion mold and germ free for a period of time, so... could I skip the hold period, especially because I cannot control the temperature without the risk of "burning" the oils?

Susan Barclay-Nichols said...

Great question, Nedeia! I've written a post here about it - I hope I've answered your question.

WhystleStop said...

RE: Micelles

In reading about the pressure cooker method, I'm wondering how leaving the phases in the same pot to reach critical temp and hold, I'm wondering how that might affect micelle formation?

Anonymous said...

How about if you don't have any water phase. Do you still recommend heating and holding?

Mark Fuller said...

Not to be contrary, but heat and hold does nothing for bacterial or microbial cleansing. To truly accomplish this, you need higher temperatures and higher pressure. Anyone who has ever used a surgical autoclave can tell you that. They run higher and they have locking doors so that they can raise the pressure.
That said, I have always "heat and held" after the phases are added. You are right about the micelle formation, but this does not begin to occur until the two different phases are combined. The oil phase alone has no real emulsification. This occurs when there are materials of disparate solubility. Heat and hold 20 minutes after adding. I would like to add that this topic was covered at an SCC Technical symposium and ir was studied at depth before coming to these conclusions.
Also if you doubt me, start reading commercial formulas on Innovadex. They all use a 20 minute heat and hold process after the heated oil and heated water phases arew combined.

Stephanie said...

This is a question about heating and holding for shampoo making. Do we heat the surfactants as well as the water? I'm not sure I understand what is meant by 'oil phase'. If I'm making 500 ml of shampoo, there will only be a little bit of essential oils added. Should I be heating them in a little eggcup in a double-boiler? Hard to use a thermometer for such a small amount.

Susan Barclay-Nichols said...

Hi Stephanie. Take a look at a few shampoo recipes in the hair care section of the blog to see where you put different ingredients. You don't heat essential oils.

Instructions for making shampoo.

Linda said...

Just out of curiosity, what would happen if you would combine the oil and water phase from the beginning inside the water bath, and heat and hold them together as a mix? I found a conditioner formula saying to do so using cetyl alcohol, sodium stearoyl lactylate and glyceryl stearate and just heat it up together with the water from the beginning. There was no oils in the formula except for fragrance, and other then water and preservative only silk protein, citric acid and panthenol.

Do you think a formula like this could work if created by this method?

Susan Barclay-Nichols said...

Hi Linda. We heat and hold separately because it creates a more stable emulsion, but you can heat and hold in the same container if you really want to do so. (See this post on the topic in the FAQ.)

As for the recipe, that's not going to make a conditioner. That's a slightly anionic or negatively charged lotion, not a positively charged or cationic conditioner. It might be a lovely lotion, but it won't condition your hair!

Aicha Diakite said...

Hi Susan, first of all let me tell you how fantastic is this blog. I am thinking about starting my own cosmetics but it is so overwhelming. I want to ask you a question and sorry if it will sound really stupid.
Regarding the heat and hold method, does it mean that once we get to 70 degree, we turn of heat and make sure to keep it at that temperature for 20 min.
Thank you

Susan Barclay-Nichols said...

Hi Aicha. Check out the instructions for heating and holding in this post. You don't turn off the heat - you want to maintain the heat of the ingredients at 70˚C.

Vidyut said...

I don't have an easy way to hold a stable temperature and didn't have a thermometer earlier and more recently broke mine and didn't have when it had to be replaced. What I do is place both containers in a pot of water and bring it to a boil. Once it is boiling briskly, I turn off the heat. Another 10 minutes later, I turn the heat on back on a low setting for a minute or two till it boils slightly and turn heat off, wait five minutes or so (water should feel too hot to be comfortable, but not impossible to put hand in briefly), and mix the two.

When I have a thermometer, I heat till it hits 80, switch off till it hits 70, then heat again, etc. But always I heat it a bit over 70 and wait till it cools a bit before mixing (heat takes a while to transfer to containers inside and the water can be hotter than the ingredients while heat is applied).

The whole time taken from the first time the water boils to mixing averages 20 minutes or so, both containers being in the same pot keeps them at a similar temperature which ought to be around 70-80 based on mostly guesswork. I call it "good enough" as I don't really think the holding at the exact temperature does much for the "baddies", so I figure if they are in a good mixing range for a wax that wants "same" temperatures.... "good enough".

wickedqueenofmean said...

I've been heating my water and oil in the oven to reach fairly easy matching temps. It's easier because the oven can be temp controlled and both phases can go in at the same time. You still have to give it some time to reach temp but it works so far. I'm a novice lotion crafter so I'm still learning.

Simone Groenenboom said...

I have a question about heating the oils and butters. The method is clear for me. heat oils and water (seperate) at 70 degrees for 20 minutes. But some butters wil not stand the heat tells the company, like shea butter and mango butter. So how about that?

thank you

Regard Simone

Simone Groenenboom said...

I have a question. its clear to heat the oil and water seperate to 70 degrees for 20 minutes. But the told me, some butters are not good with that heat like shea and mango butter. So is it oke to heat them in the oils at 70 degrees for 20 minutes?

Susan Barclay-Nichols said...

Hi Simone. As i mention in this post in the FAQ, our oils and butters can handle the low heat of heating and holding. There's nothing in shea or mango butter that can't handle heat. In fact, I haven't found an oil yet that can't be heated and held.

alia said...

how do you hold on to the same temperature for 2O minutes?

Susan Barclay-Nichols said...

HI Alia. Please read the links in the post to find out more...Or check out the Newbie section of the blog to learn how and why we do this.