## Thursday, March 3, 2011

### Question: Compensation for evaporation

Terri wrote this comment (and Priya seconded it):  My nagging question is how do you account for the loss due to evaporation of ingredients during the heat and hold? Have separate pots with just water and/or other ingredients heating as well to add later? And I never checked, but is there a change in the weight for oils,butters after the heat/hold as well? It just doesn't seem like my 100g 'experiment' doesn't equal 100 in the end.

Great question! You will see evaporation in your water phase after heating and holding; it's unlikely you'll see a big change in your oil phase after heating and holding. I wrote a little bit about surface area and evaporation in this post, but let's get into more about compensating for the water loss.

If you are heating and holding your ingredients for 20 minutes at 70˚F, you will see some evaporation from your water phase. If you add the water to the oil phase without compensating for that loss, you'll have a lot less water in your lotion - you might think you're making a 70% lotion but are really making a 60% lotion. This isn't a huge problem in the sense that you will still get a stable lotion, but it's hard to replicate that wonderful product if you don't know how much was lost.

Here's what I do. I measure out my heated water phase into my heating vessel (usually a Pyrex jug, but sometimes my awesome Christmas beaker). Then I measure the jug and water phase together so I know how much they should weigh at the end. Write this number down (believe me, you think you'll remember it, but you won't when you get into playing with all kinds of other things to kill the heating and holding time!). Start your heating and holding. In the meantime, weigh out some distilled water and heat and hold that for the 20 minutes (I'll call this auxiliary water amount to make things easier). When you take your heated water phase away from the heat, just before you add the oil and water together, weigh the heated water phase container. You'll notice there's less water in there - so add the auxiliary water amount to make up the correct amount. Make sure the water you're about to add has the same temperature as the heated and held water and oil phases before adding it. Now add the water phase to the oil phase, mix, and enjoy your lotion!

As a note, your auxiliary water amount can be anything watery like aloe vera, hydrosols, and so on, but I generally use water.

Anonymous said...

I use pyrex measuring cups and cover them with plastic wrap. I like to cover both phases. The plastic wrap sticks to the glass very well to form a kind of seal. I leave my thermometer in the cup with the plastic wrap around it and use the metal rod to stir. This method also stops any dust or "air floaties" from falling in the mixes.

Abby said...

I was recently advised to boil my distilled water in a kettle, measure out the required amount and then add this to the pyrex jug with the water phase ingredients (which has already been heated in a double boiler). The water phase and the oil phase are then both held at 70 degrees for 20 mins. I find this works for me.

sfs said...

I find I have a lot less evaporation when I use a Erlenmeyer flask for my heated water phase.

Mychelle said...

So a question I have been pondering this week: if we are accounting for water evaporation, what happens to the lovely additives in our heard water phase? As my Pyrex full of oat and silk protein, panthenol powder, etc, is heating in the other room I'm wondering if those goodies are evaporating along with my water?

Mychelle said...

Heated water phase, not heard. iPhone!

Terri said...

Thanks so much for the detailed walk-thru. You are amazing!! Feel like a mad scientist with all these separate things cooking. I second Mychelle- these hyrdosols and other lovely water based inputs will experiece evaporation, too. So you're saying even so - it's just the water that evaporates and leaves the 'goodies' behind? Can I be so bold to make a request? WOuld the list of ingredients that go into the cool down phase be short enough to put in one list?(I haven't found a keyword search on your site ,so maybe I'm missing something.) I 'cooked' the sodium lactate with the water phase the other day and noticed last night that it should have been in the cool down. ...I'd love to get a hold of some of those erlenmeyers,too.

Susan Barclay-Nichols said...

Hi Anonymous! Great suggestion! I've done this before, and it works well.

Hi sfs! Ideally, we'd use something like an Erlenmeyer flask with a small top to prevent evaporation, but those things aren't cheap!

Hi Mychelle and Terry. A lot of our lovely things like hydrosols, aloe, and so on contain a lot of water. So the water is evaporated, but the good stuff is left behind in a more concentrated way.

It's hard to make a list of cool down phase ingredients because there are so many of them, and it depends upon how we find them. For instance, we can use powdered panthenol in the heated water phase but liquid panthenol in the cool down phase. As a general rule, extracts, liquid panthenol, silicones, some preservatives, and fragrance/essential oils go into the cool down phase. (But then again, some preservatives can go and should go into the heated water or oil phase, so it's really difficult to make a generalization.)

Sodium lactate can be heated and held along with the water phase.

Terri said...

Thank you so much for answering all these questions! You are fabulous!

solquartocrescente said...

How about glycerin, tinctures can they be held in the heating water? I guess tinctures can only be added after cooling.

Anonymous said...

Hi, I'm so glad I found this blog!! Susan, thank you!
I was just wondering if anyone has experienced evaporation during mixing? I'm making a lotion that adds up to 100 grams, is that what I'm supposed to have in the end after the phases are combined and cooled?

Thanks!

Pam said...

Susan I want to thank you for all of your wonderful information!! A lot of the words are too big for me to understand but, I get the jest of it. I have been wondering about loosing some of my goodies while heating \$ holding. So glad I found this blog. I want to go make lotion right now but, it is 11PM & I need to go to bed. There's always tomorrow! Thanks again

Susan Barclay-Nichols said...

Hi Pam! I think I need a surgeon general's warning on this blog as making bath & body products is very addicting!

m. said...

Hi Susan,
I wonder if I can add magnesium chloride or arrowroot powder to compensate for water evaporation? Or do they need to be heated and held as well?
magdalena

Rosie said...

Hi Susan. You really need do that warning..:D
Thank you for this wealth of information! I don't understand most of the chemistry, but it is very inspiring.
Best wishes from Denmark

Vina said...

Hi Susan. I just realized that I completely forgot to compensate for evaporation of the aloe vera juice that my recipe called for (duh!), and have a thicker lotion than I want. Everything has cooled down to room temperature. My question is - Can I add room temperature aloe vera juice and eye balling the amount needed while mixing it with an immersion blender & checking the thickness until the desired viscosity is achieved? Will this affect the emulsification? Thanks so much.
Vina