I'll show you how to use Osmotic Pressure to gel the inside of a banana.
This also works as a great magic trick for your next party.
Step 1: What You Need
- An almost ripe banana
- Some Vodka (Better quality = better results)
- 1/4 to 1/2 cup sugar
- TupperwareÂ©-like plastic container
Ethanol is a great solvent for biological molecules.
The sugar will encourage coagulation of the liquefied banana interior.
Refer to step 4 for a detailed scientific explanation.
Step 2: Put 'em Together
Pour in the sugar and mix it until it dissolves completely.
Step 3: Cool Your Jets!
It will take anywhere from 4 to 12 hours, depending on the quality of the Vodka, amount of sugar, and the temperature of your fridge.
You'll have to try it a couple of times to get it right. If the banana is only partially gelled, leave it in for a couple more hours next time.
Don't leave it in there for too long, though. It will turn into a runny mess!
Step 4: Scientific Explanation
In this experiment we have both water (H2O) and Vodka (ethanol).
Because the peel of the banana is a semi permeable membrane, it allows the ethanol to pass through it. This is caused by the difference in the concentrations of salts inside and outside the peel.
High concentration of potassium and other salts inside the banana and the low concentration of salts outside the banana will encourage the ethanol to pass through the peel into the banana to equilibrate the system.
According to an article in Experimental Botony, 1980, volume 31, number 4, pages 975-982, the banana pulp will begin to leech electrolytes. The high concentration of potassium inside the banana will drop. This will also help the system come to equilibrium.
The coagulation of the inside of the banana is readily dependent on the temperature of the system.
Ethanol is a great solvent for biological molecules. It will dissolve some of the inside of the banana, but at the same time all the lipids will not go into solution. So it is no surprise that the ethanol makes the banana become 'softer.' It is essentially liquefying the inside.
In the process, the transition temperature inside the banana has raised above the temperature in the refrigerator. Dropping the temperature will cause the lipids and the ethanol solution to congeal.
Hence the 'gel-o-shot' like state.
For more information regarding Osmotic Pressure and Ionic Equilibrium, here are a couple of great books on the subject. (Via amazon.com)
The Osmotic Pressure of Biological Macromolecules by M.P. Tombs & Arthur R. Peacocke
Ionic Equilibrium: Solubility and pH Calculations by James N. Butler
Step 5: Enjoy!
You should notice right away that the banana feels very gelatinous inside. If it's not, then the alcohol hasn't had enough time to pass through the banana membrane and begin to liquefy the inside.
The banana will also have browned quite a bit from the cold spell. That is normal and will happen to a plain banana as well. In this experiment, the browning is accelerated by the leeching of electrolytes.
Use a knife to cut a notch right at the base of the stem, then peel it open to reveal your tasty alcoholic treat!