Remember this stuff?
It was truly magical when you were a kid, wasn’t it? I remember watching, eyes wide with awe and wonder as we squeezed that liquid goodness over ice cream and, almost immediately, it became another form of chocolate-y goodness you could crack with a spoon and crunch between your teeth.
Then, there was that time in college one of your friends bought it for erm… off label purposes only to discover, much to her disappointment, it didn’t harden at all at human body temperature?
What? Only my friends did that? Fair enough, we were mostly humanities people, we didn’t know any better. Pays to always have a chemist in your crew though I have been warned never to play pool with physicists.
I honestly didn’t give much thought as to how the various “shells” transformed until decided to introduce it to my kids. I made my own because I didn’t particular want them eating paraffin wax, food grade or no. I’m a tox nurse and I’m well aware that a little bit of wax isn’t going to hurt anyone, but if I wanted to eat it, I’d recycle those used birthday candles, thank you very much. Some commercial grade products have already replaced the wax with a plant based oil (Carvel, for example, has done this per Chowhound.com. Smuckers, the grocery store brand I see most frequently, declined to discuss their proprietary blend which makes me think they’re either still using wax or some sort of soylent something), but then you have to stand in the aisle and read ingredients and one kid is making a break for some sugar based Star Wars cereal and the other has decided to teach himself to juggle with the eggs…
The chemistry behind the wax and oil emulsifiers is essentially the same, which is why it’s easy to substitute the later for the former. Provided you use the right kind of oil.
You ready for me to lay the science down? Here we go:
Chocolate is the other constant (there are other flavors but why screw with a classic?) in the various ice cream shells. Chocolate, by its nature, contains a fair bit of fat, milk more than dark, but even dark has a goodly bit. Why is the fat already in chocolate not sufficient for our shell purposes? I’m taking a leap here, but after some research, it seems to me that shell needs the additional emulsifier for two reasons: 1) the fats native to chocolate are are of the more stable sort and don’t change phase easily or quickly enough for the shell to be fun rather than an eternal waiting game and 2) chocolate doesn’t have enough emulsifiers to add “tenderness” to, well, itself. Chocolate melted on its own does change state but it eventually dries out and get lumpy and/or gritty. The additional emulsifier in magic shell, much like the cream in ganache, keeps it it from dehydrating and congealing.
Per Paula Figoni’s How Baking Works, oils are, “any lipids that are liquid at room temperature,” (pg. 215). Oils are usually vegetable based (canola, corn, olive). Most are liquid at room temperature. Tropical oils (coconut, palm, etc), however, are solid at room temperature but melt quickly and within a relatively small temperature window: solid at 70 degrees F, liquid at 74.
Chemically speaking, all oils are trigylcerides: three fatty acids attached to a three-carbon glycerol molecules. Fatty acids are made up of carbon chains that have anywhere from four to twenty-two carbon atoms. Saturated fatty acids are “saturated” with hydrogen atoms (they can’t hold any more) which means all of the carbon bonds in the molecules are single bonds. Unsaturated fatty acids contain carbon atoms that are not fully saturated with hydrogen; carbon atoms that are not saturated form double bonds in order to maintain structural integrity. Double bonds create stronger atoms, stronger atoms create stronger molecules and stronger molecules create stronger substances. Due to the aforementioned, double bonds are also more difficult to break and if you want to split them to force a change of state, you have to use more energy than you would to break a single bond.
That’s why coconut oil, which is high in saturated fats, is frequently used as the emulsifier in Magic Shell; single bonded as it is, it can be broken down from a solid to a liquid with very little expenditure of energy – or just a four degrees of heat. The bonds reform with a proportionately small drop in temperature, allowing the shell to harden almost upon contact with a frozen dessert (or an ice cube if you’re just testing for funsies).
When I made my shell, I subbed olive oil because that’s what I had around. Coconut oil is a little spendy and I was hesitant to shell (heheh) out for a whole container; oils do go bad and odds of that happening before I used the whole container, even a small one, were good. Because vegetable based oils are lower in saturated fat, and thus carry double bonded carbon atoms, however, it takes more energy, and hence a greater temperature differential, to force a phase change. It worked, to an extent, but it was really cold in my house at the time, cold enough to solidify even the olive oil, which meant I had to re-melt every time I wanted to use the shell (which eventually lead to dehydration and grittiness) and then the kids had to wait a good five minutes from application to re-shelling. And, as we all know, things are only magical when instantly gratifying. They thought it was cool, but not as cool as I’m sure they would have if it had been essentially immediate.
Yay for books!
Yay for chemistry!
Yay for shell!
How Baking Works: Exploring the Fundamentals of Baking Science is by Paula I. Figoni. It was originally published in 2004 by John Wiley & Sons Ltd. I have used, quoted from, and now purchased the 3rd edition, originally published in 2010. I’d be happy to share.
Have other cooking or baking questions? Shoot me a line. I’m always looking for new topics.