Kitchen Chemistry Class
Image Credit: This gorgeous olive oil caviar was made by Chef Ferran Adria, leader and inventor in the field of modern gastronomy.
The following is supplementary information, to extend class work and lab work for my culinary students.
But if you are interested in doing some at-home science experiments, this is a fun place to start. The more kids learn about the foods they put in their bodies, the better! Knowledge equips us to make better choices. Plus, why not get the kids doing more kitchen work, especially when it is so much fun! Seriously, I suffered through a lot of, let’s say “interesting” dishes while my kids were learning to cook… but now they can cook for me! 😀 Method to my madness.
Feel free to use this information at home and be sure to check out the sources at the bottom of the page.
And hey, we do even more cool stuff in the class, so if you can schedule a class, go for it! And I will do the work for you.
Question:
What happens when a solution containing sodium alginate is dropped into a solution containing calcium chloride?
What We Will Learn
- Spherification to create little liquid-filled spheres.
- How to use properties of dispersion to create solutions
- Chemical reaction that takes place when sodium alginate and calcium chloride are combined
- How acidity and calcium interact with these chemicals.
- A cool new trick to WOW your friends.
Vocabulary
solution – when one substance is completely dissolved in another, such as when sugar is dissolved in hot wate
dispersion – mixture in which fine particles of one substance are scattered throughout another substance
hydration – each molecule is surrounded by water
sodium alginate – a natural gelling agent taken from the cell walls of certain brown seaweed species. This salt is obtained by drying the seaweed, followed by cleaning, boiling, gelling and pulverizing it. A light yellow powder is produced from the process. (from amazingfoodmadeeasy.com)
calcium chloride – a white crystalline salt used as a food preservative, to de-ice roads, and as a drying agent
polymer – a substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together
hydrocolloid – a substance that forms a gel in the presence of water
pH – a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid, and higher values more alkaline.
This is Sodium Alginate
It comes from seaweed that has been dried and ground up.
Sodium Alginate is used in medicine, printing, paper making, and in food as a thickener, stabilizer or binder.
This is Calcium Chloride
In 1861, a Belgian chemist named Ernest Solvay, invented a process for producing sodium carbonate which was used for making glass. He used an acid brine on limestone to do this. It so happened that this process also produced Calcium Chloride, which is now used in food as a preservative… it keeps food from going bad.
The Solvay process for making calcium chloride looks like this…
But frankly, this is way over my head!
It is easier to just remember that calcium chloride is a salt made from a chemical process.
Now for the cool part!
When you combine sodium alginate with calcium chloride, a chemical reaction occurs and a new thing is created! Sodium alginate molecules link together to form chains. Calcium chloride connects the chains together to form a gel.
You get this:
The calcium chloride kind of sandwiches itself in between the sodium alginate.
If it were a peanut butter sandwich the alginate would be the bread and the calcium chloride would be the peanut butter that sticks it together.
If it were a carton of eggs, the alginate would be the carton and the calcium chloride would be the eggs inside.
Sodium alginate (NaC6H7O6) reacts with calcium chloride (CaCl2)
to make calcium alginate (C12H14CaO12), which is a gelatinous substance.
2NaC6H7O6+CaCl2→2NaCl+C12H14CaO12
The two chemicals have rearranged so they are bond together (like puzzle pieces)
and form a gelatinous (like jello) substance.
A drop of liquid (like juice) mixed with sodium alginate that falls into a calcium chloride bath creates a sphere.
This sphere will have a thin layer of gel wrapped around liquid! When you cut into it, the liquid flows out. When you bite it, it pops in your mouth.
You can make something that looks like an egg yolk, but is in fact, melon juice… like this one from Molecular Recipes.
Or colorful caviar spheres…
Or fish-free olive oil caviar by Ferran Adria… who developed this process and made it famous.
Edible Chemistry in Action!
As soon as the droplet with the alginate solution touches the calcium bath, the two react! All around the outside of the sphere, they quickly form a bond which makes a thin film holding the liquid inside. This happens in only a few seconds!
This new substance is called Calcium Alginate.
At this point, you need to use a strainer to remove the spheres from the calcium bath and gently rinse them. Then they should be eaten immediately. Why? Because if you let them sit, the calcium on the outside will work its way through, turning the entire sphere into a gel. You can still eat it but it just wont pop in your mouth with a liquid surprise. It will be more like a little sphere of jello.
Lab Work – Basic Spherification
You will need:
- gram scales
- distilled water (contains no calcium)
- sodium alginate
- calcium chloride
- juice, pH over 3.6 (experiment with different types and note the results)
- mixing bowls, rinsing bowl
- plastic wrap
- blender, or immersion blender
- fine mesh strainer
- pipettes or spoons
Procedure
Step One: Prepare ingredients
- Create a .5% solution of sodium alginate and juice. (5 grams sodium alginate to 1000 grams juice)
Example: If you have 17 to 18 ounces juice (500 grams), use 2.5 grams sodium alginate
Use a blender to be sure the sodium is completely dissolved, or dispersed. Pour solution into a bowl, cover with plastic wrap and allow it to sit in the refrigerator for 1 to 24 hours, long enough to allow air bubbles to escape. (to be precise, 17.637 ounce = 500 grams) - Make a calcium bath by preparing a .5% solution of calcium chloride and distilled water. (5 grams calcium chloride to 1000 grams distilled water) Be sure solution is well dispersed.
Example: If you are using 35 ounces of water (1000 grams), add 5 grams calcium chloride - Prepare a bowl of plain distilled water to rinse spheres.
Notes: When you are working with chemicals, be careful to not contaminate one with the other. Use parchment paper or little cups on the scales to be sure they do not mix while measuring. Also, keep calcium chloride sealed quickly after removing your measure, as it will react to any humidity in the air.
Step Two: Making spheres!
Fill a pipette or syringe with the juice solution. Hold it over the calcium bath, about 3 inches from the surface, being careful to not touch the tip to the bath. Create droplets, letting each one fall into the calcium bath. You can make larger spheres with a spoon. Use a paper towels under the spoon to remove excess solution and gently place the spoon to the surface of the water. Flip the spoon. This may take some practice.
Allow droplets to sit in the bath for about one minute to develop a thin skin. Allow larger spheres to sit for about 2 minutes.
Using a strainer, carefully remove spheres from the bath. Gently rinse them in to plain water to remove bitterness from the calcium chloride.
Serve immediately!
The little spheres will continue to gel. After about 10 or 20 minutes, they may become solid. losing the pop from a liquid interior. If you do wish to store them, it is best to store them in juice or oil, rather than water. (using the same type of juice you used to make them)
Notes
- pH of the liquid used must be above 3.6. Acidic liquid may not gel. You can add an alkaline ingredient such as sodium citrate to the liquid to raise the pH. Sugar can raise the pH.
- Avoid liquids with excess calcium. Too much calcium will make the liquid gel before you pour it. You could fix this by adding a sequestrant, which is a compound that mops up excess calcium ions by binding them so that they cannot interact with other molecules.
- We are using calcium chloride, because is contains the most calcium – 36.1% – other calcium compounds will work, like calcium carbonate, but they just require a different ratio/recipe.
- When the two chemicals come into contact with one another they rearrange so that the alginate binds to the calcium, forming calcium alginate, which is a gelatinous substance.
- You can also make spheres using agar agar (also from seaweed) and cold oil! See how here.
- You can learn about Reverse Spherification Here.
- Do expirement with a variety of juices or liquids and note your results. Can you figure out why some work better than others?
- There are different ways of creating spheres, using various chemicals and methods. Check out this one using cold oil and agar. Caviar by Cold Oil Spherification
Sources
- Molecular Recipes Spherification
- Chef Steps The Science of Spherification
- Its Chemically Delicious! The Science Behind Spherification
- Juice Caviar For Less Molecular Gastronomy Spherification
- Blogspot The Exploration of a Gastrochemist
- Seaweed image from Viipra Chemicals
- Hands image from Scentses
Where to get Sodium Alginate and Calcium Chloride.
Your best bet is to order online. Be sure to find a product that is food grade. Here are some that I have used.
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