Gourmet Chemistry, The Chocolate Version

Another recipe from the fancy new-age molecular gastronomical kitchen.
This time for the sweet tooth experimentalist.


spherification_bYou’ll need:

  • 1.2 g sodium alginate
  • ¼ cup calcium free chocolate syrup (non-dairy syrup)
  • ¼ cup water
  • 5 g calcium chloride
  • 2 cups water

Let`s do it:

  1. Dilute ¼ cup (60 mL) chocolate syrup with ¼ cup (60 mL) water.
  2. Blend in the sodium alginate thoroughly using the hand mixer.
  3. Set aside to allow the trapped air bubbles to escape (may take a few hours).
  4. Make the calcium bath by dissolving the calcium chloride in 2 cups of water.
  5. Prepare the rinsing bath by filling a bowl with cold water.
  6. Now make the spheres:
    1. Scoop a teaspoon of the chocolate mixture and drop it into the calcium bath. The more spherical the teaspoon you use, the more symmetrical your balls will be.
    2. Let the balls sit in the bath for a minute or two.
    3. Transfer the chocolate balls to the water bath. Use a skimmer or try to decant as much water as possible. Let the balls sit in the water bath for few minutes.

What a treat!

What’s going on here?

Dropping the chocolate-alginate solution into the calcium bath solidified it on the outside, forming a shell and trapping the liquid inside. How? Did we mention Polymer chemistry already?

So what are polymers? A polymer is a long molecule made from a repeating unit (molecules). Polymers are found in nature, like DNA, wood and wool as examples, or can be made synthetically such as all kinds of plastics. A polymer can be relatively short like proteins or extremely long like a car tire which is made of only one molecule (!).

Back to our experiment, alginate is a polymer. It is derived from brown algae and contains repeating units (molecules) of sugar, which in scientific language is called polysaccharide. Under certain conditions, each of the repeating units in the alginate contains free negative charge which can be pictured as hands, free to hold only positive charges. And that’s where the calcium in the bath comes into the picture. In this case the calcium is in the form of ions, meaning each one of these ions has 2 positive “free hands”.

So… when the chocolate-alginate solution is dropped into the calcium bath and the calcium and alginate meet, they start to hold hands. Now, think about the long strings of alginate being held by calcium. And every calcium ion can hold the 2 alginate hands. What does it sounds like? You bet it, a mess! Just like a ball of entangled yarn. This mess, which starts to form on the outside of the ball, actually looks like a web that holds the liquid inside and doesn’t let it mix with the water in the bath. This process of calcium attaching to the alginate is referred to in science as cross-linking and the resulting mess is what scientists define as gel.

Keep on experimenting:

How does the time in the calcium bath affects the texture of the chocolate balls?

Try it out and let us know.