Arrested Development returns! / Chocolate and peanut butter frozen bananas and hydrophobicity

In celebration of the new arrested development season, I thought it'd be most appropriate to post some quick tips on making your own Bluth frozen banana.

Bluth frozen banana stand, Columbus Circle NYC. Pretty tasty,  apparently made by the company 'Totally Bananas'

The whole process is greatly accelerated if you have access to any liquid nitrogen, but otherwise using an ordinary freezer is fine.  Start by halving peeled bananas and running Popsicle sticks or chopsticks through the center.  Keep these in the freezer for 2 hours, although overnight makes the following steps easier.

Once your bananas are frozen, you could coat these with melted chocolate immediately, but here is where a bit of science helps.  Dark chocolate contains ~30% fat components, which makes it relatively hydrophobic. If you've ever seen oil and water forming separate layers and not mixing, it is because fat is hydrophobic (fats generally contain long non polar carbon chains, while water is small, polar, and can form hydrogen bonding networks).The longer a frozen banana is removed from the freezer, the more ice on the surface will melt. When these small droplets of water hot melted chocolate, they cause it to "seize up", or become hard and lumpy. This is because fats within the chocolate are trying to minimize contact with water molecules and minimize disruption of hydrogen bonding networks, which is thermodynamically unfavorable.

Left: An example of a fat-water interface.  The orange and yellow molecules are fat molecules, with multiple  chains of yellow carbon atoms.  The red (oxygen) and blue (hydrogen) molecules are water, which can form hydrogen bond networks (dotted line).  The two types of molecules separate out creating an interface, shown with a solid line.  Right: A very small amount of water is introduced into a mostly-fat environment, the water molecules arrange to maximize hydrogen bonds, fat molecules arrange themselves to minimally interfere.

Some solutions to the chocolate seizing problem: if you used liquid nitrogen to freeze dry your bananas, the frozen water on the banana surface would sublimate (turn into gaseous water vapor) rather than for liquid water droplets, avoiding the problem. The approach I used was to have a buffer layer between the banana and the chocolate, by spreading a thin layer of peanut butter on the banana prior to chocolate coating.  For technique, I would recommend using a cake-frosting strategy of placing a large lump of peanut butter on the banana and then spreading it thin, rather than trying to do several single thin strokes, and
doing this with bananas frozen overnight (peanut butter will have some difficulty sticking as water droplets form, but likely will not seize as most peanut butter brands contain some kinds of emulsifiers).  Chill the peanut butter coated bananas in the freezer for about 15 minutes.

Peanut butter spread on frozen banana on chopstick

When it comes time to coat with chocolate, I'd recommend melting about 1/4 cup of dark chocolate per banana half.  Melt this in the microwave at 20 second intervals, stirring each time, until you just reach the point when all the chocolate has melted (any further and it will likely burn).  Some other recipes I've seen have advocated mixing in butter or coconut oil or other components, but I find these to not add much to the flavor of the shell and at times, interfere with proper hardening or spreading of the shell.  Either dip your peanut butter bananas into the melted chocolate, or if working with a small batch, just spread the melted chocolate on with a knife (as I did, a bit less presentable).  You can also dip frozen bananas without the peanut butter coating, but would have to work fast - dip each one immediately after removal from the freezer. This is also a good time to add a sprinkling of nuts, shaved coconuts, candies, whatever. Allow these to chill in the freezer for another 15 minutes, then serve.

A messily chocolate and peanut butter coated frozen banana. For a smoother chocolate coat, melt more chocolate and dip rather than spread