Friday, January 14, 2011

Surface area and our products

You probably saw the post the other day on the min-maxed toner becoming a moisturizing gel (which I'm still very much enjoying) and probably saw this picture of it in a Pyrex jug. Don't leave your products in a container like that for too long before bottling!

Evaporation tends not to be our friend in situations like these. Leaving the product in an uncovered, wide mouthed container like this leaves our products susceptible to losing a lot of water in a short period of time. The warmer the room, the more water loss we'll see. A product like this, one that's high in water content, can lose a ton of water in a very short period of time - even in our darn it the furnace is broken and it's snowing outside so it's only 16˚C or 62˚F in the house right now temperature this week, I went from having about 91 ml of product to 85 in two days!

You could use this to your advantage - if you have a bubble bath, body wash, shampoo, or other surfactant mix that needs some thickening, you can use the power of evaporation to reduce the amount of water in the product over time - but then you leave the product open to contamination (check out this post on contamination and packaging), not to mention things like bugs or particles from the air dropping into it! (And when I say bugs, I don't mean little ones like bacteria or fungus, but big ones like flies! These little creatures seem to get curious in my workshop at night, and I've found all kinds of weird things in my unused Pyrex jugs when I reach for them! Yuk!)

Think about surface area when you're heating and holding your products. For something like the water phase of the lotion, the larger the surface area, the more evaporation you'll see. If you want to heat 250 ml of water, it's better to use a tall container than a shallow flat one - if you were using Mason type jars, a standard sized jar is better than a wide mouth in this situation. Using something like this Erlenmeyer flask will reduce how much evaporation you see in your water phase. (And will look seriously awesome and science-y!)

Having said that, a larger surface area can be your friend when you're heating your oil phase because we're not as concerned with evaporation when it comes to oils, butters, esters, and so on. Depending upon the ambient air temperature, using a larger, flatter container in your double boiler means you can mix in those larger chunks of butters without removing the product from the heat! (If it's really cold in your workshop, a larger surface means this has time to cool when the temperature is very low, so follow this advice only if you're in a reasonably heated room! I've had BTMS-50 cooling on the sides of my container while the liquid under the surface is at 70˚C!)

And if you ever feel like getting me a present, a set of 250 ml and 500 ml Erlenmeyer flasks would be a welcome gift indeed! 


Anonymous said...

Hi Susan, Regarding evaporation, when i make anhydrous butters containing oils, butters and waxes, i seem to lose about 10% of the product each time. There is no water in my recipe and i weigh it out in percentages, usually making just one pot of 100grams, so my grams equal my percentages. I heat to 72C and hold for a couple of minutes. Each time i am left with about 10% less, about 90grams of product. Any ideas why this might happen? Thanks as always, Rachel.

Susan Barclay-Nichols said...

Hi Rachel. I really can't think of a reason why this is happening as oils don't evaporate. You're only heating for a short period of time, so there's no time for anything to evaporate. Are you measuring it with a spoon or something in the container and removing the spoon or something when you measure it after heating? That's the only thing that would make sense...