Do you enjoy getting creative in the kitchen? If so, this activity is for you! Molecular cuisine—taking tools, ingredients and methods typically used in science and using them in cooking—might sound fancy and complicated, but some techniques are easy to replicate! Get your hands wet, fire up your creativity and see how rewarding it can be!
Molecular gastronomy—the science of culinary phenomena—brings scientific procedures, ingredients and instruments into the kitchen. Part of this field studies the influence food preparation techniques have on texture and flavor. Spherification of juices, changing a liquid into semisolid pearls, is one example. The most common method uses two chemicals, such as sodium alginate and calcium chloride: One chemical is dissolved in the liquid and another in a water bath. When drops of the treated liquid fall into the bath they form small spheres. The outside of these spheres solidifies as a result of a chemical reaction between the two additives. There you have it—little drops of liquid confined in a thin, solid membrane!
One can also make gel-like spheres using more common ingredients: gelatin and oil. Gelatin is made of the protein collagen, a large fibrous molecule abundant in many animals, including humans. Collagen makes skin, bones and tendons strong and somewhat elastic. This large protein is partially broken down and further treated to form gelatin. When gelatin is prepared, its proteins unravel as a response to added heat. These long strings interlace when cooled, however, and create a three-dimensional structure that can trap a lot of liquid. If prepared with water, the resulting gel is transparent, colorless and flavorless. In the kitchen it is often used for its unique texture.
- Unflavored gelatin powder, two seven-gram packages
- Water or juice, one-half cup
- Food coloring (red, blue or green work well)
- Vegetable oil, four cups
- Four tall containers
- Ice cubes
- Saucepan or microwavable cup
- Stove or microwave
- Dropper or syringe
- Slotted spoon
- An adult helper
- Work area that can get wet
- Red cabbage (optional)
- Pour about two cups of vegetable oil into each of two tall containers.
- Place one container in the freezer for at least 30 minutes.
- Fill the other two containers with about two cups of water each.
- Add ice cubes to one container to cool the water.
- To prepare the gelatin, pour one-half cup of liquid (water or juice) into the cup or saucepan. Add two packages of gelatin powder and stir until all the powder is dissolved. Add food coloring so you can easily see the pearls in the water or oil. Have an adult helper carefully heat the liquid on the stove or in the microwave until it is very hot while stirring occasionally. Let the gelatin cool for five to 10 minutes.
- Have the dropper or syringe, the four containers—two filled with water and two filled with oil—and the warm gelatin nearby. In a minute you will put a few drops of warm gelatin into each container. What do you think will happen?
- Use the dropper/syringe to put a drop of warm gelatin into each of the containers and watch what happens. Repeat this until you have added three drops to each container. Do you see little pearls form in some liquids and not in others? Does something similar happen each time? Why do you think this happens?
- Let the drops sit for a minute, then see if you can scoop the pearls out with a slotted spoon. Which liquid allows you to form gelatin pearls? Why do you think this is the case?
- Rinse the pearls with water and try tasting one. How do your gelatin pearls taste? What is the texture like?
- Use the leftover warm gelatin to make more gelatin pearls. Try to make different size pearls or gelatin spaghetti. Recool the oil that was in the freezer in between batches if needed.
- Extra: Can you improve the taste of your gelatin pearls? What oil and what liquid would make a great combination? Can you also change the texture?
- Extra: Watch your gelatin pearls shrink as they dry out. Put them back into water to see them swell again. Why do you think this would happen?
- Extra: Prepare red cabbage juice by boiling the cabbage in plenty of water. After the water has turned purple, use it to make red cabbage juice pearls. Discover how these pearls are special by placing them into vinegar and/or a baking soda solution. Can you also explain your observations?
- Extra: Look up other spherification methods using sodium alginate and calcium chloride. Order these chemicals or a spherification kit and make juice balls or yogurt ravioli.
Observations and results
Did droplets of warm gelatin only form nice pearls in the cold oil whereas dropping them into water or room temperature oil failed to form pearls?
To prepare the gelatin, you dispersed gelatin particles homogeneously in the liquid you used for this activity (water or juice). These particles unravel into long strings when heated. If they are concentrated enough, a gel forms as the gelatin interlaces and creates a three-dimensional structure that traps liquid as it cools. When warm gelatin is dropped in water the particles spread out over all the water and their concentration becomes too low to solidify. When warm gelatin is dropped in oil however, the gelatin stays together in little spheres. This happens because water and oil do not mix. Gelatin particles shy away from oil so they clump together in the shape that gives the least possible interaction with oil: a sphere.
In addition to the concentration the temperature of the solution matters. Gelatin needs to cool below a specific temperature to solidify. Cold oil provides the necessary cooling but room temperature oil does not. As a result you can scoop out nice solid gelatin pearls from the cold oil bath—but not from the room temperature oil bath nor the water baths.
Pour the cooking oil into a container and bring it to your local recycling center or dispose of it in your garbage. (Never pour cooking oil down the sink drain! It clings to the pipes and solidifies in time, leading to pipe blockages.) Wash all equipment with water and soap.
More to explore
Boba Spherification: The Science of Juice-Filled Caviar, from Science Buddies
You Can Do That with Yogurt?, from Science Buddies
What Is Jell-O? How Does It Turn from a Liquid to a Solid When It Cools?, from Scientific American
Sweet Science: Making Marshmallows, from Scientific American
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies