Have you heard about molecular gastronomy? Yah… this fancy food served in gourmet restaurants. Here’s an easy recipe to try. It’s all about polymer chemistry!
2 cups water
4g Sodium alginate
¼ cup milk
½ tbsp calcium lactat
1 tbsp olive oil
1 tsp white-wine vinegar
1 tbsp chopped dill
1 garlic clove
½ cup yogurt
2 cups of water
First prepare the alginate bath:
Just dissolve the alginate in the water. But, it should be thoroughly mixed, so use a blender or hand mixer.
Refrigerate for 15 minutes.
Then prepare the tzatziki mixture:
Easy peasy as well. Mixed all ingredients and season to your taste. Refrigerate for 15 min.
Now for the fun part:
- Scoop a teaspoon of the tzatziki mixture and drop it into the alginate bath. The more spherical the teaspoon you use, the more symmetrical your balls will be.
- Let the balls sit in the bath for 3 min. Roll them, to make their texture even.
- Transfer the tzatziki balls to the water bath, and let it sit for 5 min.
- Take the balls out of the water and serve over a slice of cucumber.
What’s going on here?
Dropping the yogurt mixture into the alginate 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 yogurt mixture comes into the picture. Remember adding calcium lactate to the mixture? Well, 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 tzatziki mixture is dropped into the alginate 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.