Abstract
Imagine if instead of spooning up a bowl of soup, a container of yogurt, or a cup of pudding you could just pick up and pop in your mouth a round, mess-free, ball-like blob of one of those. It might feel like snacking rather than eating a meal! In this food science project you can try exactly that. The simple step-by-step directions will lead you through trying a fun cooking technique called reverse spherification to turn yogurt into semi-solid balls, which are called "raviolis." How do you think the yogurt raviolis will look and feel? Get ready to make this unique snack to find out!Summary
Teisha Rowland, PhD, Science Buddies
- Coca-Cola is a registered trademark of The Coca-Cola Company.
Objective
Investigate how "raviolis" made from yogurt change over time.
Introduction
Did you know that you can turn just about any food into little self-contained spheres (balls)? Creative chefs who like to combine science with interesting ways to present and experience food have pioneered a technique called spherification. Spherification uses chemistry to transform soft, liquidy foods like soup, purees, juices, yogurt, and pudding into balls. The balls have a thin, flavorless gelatinous outer skin or membrane, which you can easily pop open in your mouth to get to the liquid center. Spherification, and a related technique called reverse spherification, are part of a bigger food movement called molecular gastronomy. Molecular gastronomy is the area of food science that explores how ingredients in our food are physically and chemically changed when we prepare and cook them. In other words, molecular gastronomy looks at the tiny molecules in our food and how they change under certain conditions. (Gastronomy is the study of picking, preparing, and eating good food.) Figure 1 shows spheres that have been made out of green tea using spherification.
Figure 1. These are spheres of green tea that have been made using spherification. (Image credits: Wikimedia Commons, Jlastras, 2009)
How does spherification work? Like much of food science, it is based on a specific chemical reaction. During spherification the food you want to turn into balls is mixed in a blender with sodium alginate. Drops of the mixture are then put in a bowl containing calcium dissolved in water. As soon as the sodium alginate and calcium come in contact with one another, they undergo a chemical reaction and form a thin gel-like shell surrounding each drop of the food mixture. The result is spheres of the food that you can fish out of the calcium bath, rinse, and eat. For more details on the chemistry involved, you can check out the related Science Buddies project Make Popping Boba Balls Out of Your Drinks.
In this science project, you will make "raviolis" out of yogurt using a complimentary technique, reverse spherification, and investigate how this chemical reaction makes the yogurt raviolis change over time. Reverse spherification is used when a food already has calcium in it, like yogurt. During reverse spherification a calcium-rich food is dropped in to a bowl containing sodium alginate dissolved in water. (This is, as you can see, the opposite or reverse of normal spherification.) The same gel-like shell forms around the food as the calcium and sodium alginate react with each other. To summarize, spherification involves adding a mixture of food and sodium alginate to a calcium bath, while reverse spherification involves adding a food that already has calcium to a sodium alginate bath. To learn more about reverse spherification and to see what this process looks like, check out this video.
In this project, because you are dropping spoonfuls of yogurt rather than small droplets of a food mixture in to the sodium alginate bath, the results will be larger blobs of food instead of tiny spheres. The blobs resemble pasta raviolis and are referred to as "raviolis" by molecular gastronomy chefs. If the yogurt sits in the sodium alginate solution for increasingly longer amounts of time, how does this affect the gel-like layer that forms around the yogurt? Will the yogurt get a thicker gel-like layer over time, making the raviolis bigger? Or will the gel-like layer not change size once it forms? You will use a digital scale and weigh your homemade yogurt raviolis over time to find out. So get ready to make some fun, yogurt snacks!
Terms and Concepts
- Spherification
- Reverse spherification
- Molecular gastronomy
- Chemical reactions
- Sodium alginate
- Calcium
Questions
- What are the key chemicals needed for the spherification reaction?
- Where do alginates come from?
- What type of foods do you think would work well in reverse spherification?
Bibliography
To find out more about molecular gastronomy and reverse spherification, you can check out these resources:
- Molecular Recipes Staff. (n.d.). Reverse Spherification. KQ2 Ventures, LLC. Retrieved April 26, 2018.
- ChefSteps. (n.d.). Demonstration of Reverse Spherification. Retrieved October 2, 2014.
- Molecular Recipes Staff. (n.d.). Spherical Yogurt Recipe. KQ2 Ventures, LLC. Retrieved October 2, 2014.
To find out more about chemical reactions, see these resources:
- Rader, A. (n.d.). Chemical Reactions. Rader's Chem4Kids.com. Retrieved October 2, 2014.
For help creating graphs, try this website:
- National Center for Education Statistics, (n.d.). Create a Graph. Retrieved June 25, 2020.
Materials and Equipment 
Recommended Project Supplies
- Spherification Kit, available from our partner
Home Science Tools.
You will need these items from the kit:
- Sodium alginate (2.9 g)
- Note: The kit contains enough supplies to also do several other fun food science projects. See the kit instructions page for details.
- You will also need to gather these items, not included in the kit:
- Blender; it should ideally hold at least 3 C, but smaller blenders can also be used. If you are using a smaller blender, you will also need a fork and a bowl or container that can hold at least 3 C of liquid.
- Digital scale with 0.1 g increments. A digital scale that would be suitable is the Fast Weigh MS-500-BLK Digital Pocket Scale, which is available from Amazon.com.
- Wax paper (1 sheet)
- Distilled water (3 C); available in your grocery store
- Liquid measuring cups
- Plastic wrap
- Refrigerator
- Plastic cups, 8 oz (4)
- Scissors
- Permanent marker
- Vegetable oil
- Paper towel
- Round measuring tablespoon
- Butter knife with one straight edge
- Spoons (at least 3)
- Yogurt (at least 4 tbsp.); the yogurt should have at least 20% DV (daily value) of calcium, as shown on the nutritional label on the container. Only one type and container of yogurt should be used in this science project.
- Optional: Camera
- Optional: Adult helper for using the blender
- Lab notebook
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Experimental Procedure
Preparations
In this part of the science project, you will prepare your solutions and plan your experiment. It might be helpful to watch the reverse spherification video for an introduction and overview of this project.
- Make the sodium alginate solution.
- Note: You will need to use a blender that can hold at least 3 cups (C) or a smaller blender that you can make multiple, smaller amounts of sodium alginate solution in at a time (to add up to 3 C total).
- Weigh out 2.9 grams (g) of sodium alginate.
- To weigh out the sodium alginate, cut a small piece of clean wax paper (around 8–10 centimeters [cm] on each side), place the wax paper on the scale, zero out the scale (so that it reads "0 g"), and then weigh out the chemical on the wax paper. Use a clean spoon to scoop the chemical out of its container. Note: You should use wax paper because it is harder for chemicals to stick to than normal paper.
- Tip: If the scale you are using does not have a feature to zero it out, you will need to first weigh the piece of wax paper so that you can subtract this mass from the total when you weigh the chemicals on it.
- In the cup part of a blender, add 1/2 C distilled water.
- Add a little bit of the 2.9 g of sodium alginate that you weighed out to the blender cup, as shown in Figure 2.
Figure 2. To the blender cup, add ½ C distilled water and a little sodium alginate.
- Have an adult help you use the blender to blend the water and sodium alginate together until the solution is completely smooth and well-blended, as shown in Figure 3.
Figure 3. Blend the sodium alginate with the water until they make a smooth solution.
- Repeat steps 1.c.–1.e. until you have added and blended a total of 3 C of distilled water and the entire 2.9 g of sodium alginate together.
- Adding a little bit of the sodium alginate at a time will ensure the solution is well-mixed.
- If you are using a blender that cannot hold at least 3 C, pour the blended solution into a clean bowl or container each time the blender cup is full. When all 3 C of the sodium alginate solution has been added to the bowl, mix it with a fork for several seconds.
- Cover the sodium alginate solution (with a lid or a piece of plastic wrap) and place it in the refrigerator. Let it sit in the refrigerator for at least 2 hours, but as long as overnight, before testing it with the yogurt.
- Letting the solution sit will allow the air bubbles to escape from it, making it ready to use.
- While the sodium alginate solution sits in the refrigerator, plan out what times you will be weighing the yogurt in your experiment. You will be weighing the yogurt raviolis to see how the reverse spherification reaction changes the yogurt raviolis over a period of 24 hours, specifically to see if the raviolis change in mass. Examples are given in step 3.c. Keep your schedule and the following tips in mind as you plan your time checkpoints:
- You should let the yogurt sit in the sodium alginate solution for at least 24 hours total.
- You should use at least five time checkpoints.
- One of these time checkpoints will be at the beginning of the experiment, before you put the yogurt in the sodium alginate solution.
- Another time checkpoint will be at the end of the experiment, after 24 hours.
- You will want to space out your time checkpoints by at least one hour, but keep in mind that you will be unable to take measurements while you are asleep or away from your experiment.
- For example, if you started the experiment in the morning and were around to take measurements all day and the next morning, you could do measurements at 10:00AM, 1:00PM, 4:00PM, 7:00PM, and then 10:00AM the next morning. (These measurements would be after 0, 3, 6, 9, and 24 hours [hrs].)
- As another example, if you started the experiment in the late afternoon and were around later that day and the next to take measurements, you could do measurements at 5:00PM, 6:00PM, and 8:00PM, and then at 4:00PM and 5:00PM the next day. (These measurements would be after 0, 1, 3, 23, and 24 hrs.)
- Now prepare the cups in which you will be testing the yogurt over time.
- Take four 8 ounce (oz) plastic cups. Carefully use scissors to cut the tops off of each cup so that they are only 6 centimeters (cm) tall. For an idea of how these cups should now look, see Figure 4.
- Use a permanent marker to label the little cups 1, 2, and 3. The fourth cup can be unlabeled; you will be using it to practice making yogurt raviolis.
Testing Reverse Spherification with Yogurt
In this part of the science project, you will investigate how the reverse spherification reaction changes the yogurt raviolis over time. To do this, you will put a spoonful of yogurt in the sodium alginate solution and weight the yogurt at different times over 24 hours. Do you think the gel-like layer around the yogurt will get bigger, resulting in heavier yogurt raviolis over time? It is time to find out!
- Before starting your experiment, make a data table like Table 1, in your lab notebook. You will record your data in this data table.
| Mass Over Time (g) | |||||
| Yogurt Samples | 0 hrs | 3 hrs | 6 hrs | 9 hrs | 24 hrs |
| 1 | |||||
| 2 | |||||
| 3 | |||||
| Average | |||||
- When the sodium alginate solution has sat for at least 2 hours and you are ready to start your experiment, use a clean liquid measuring cup to fill each of the cut-off plastic cups (which you prepared in step 4 of the Preparations section) with 2/3 C of the sodium alginate solution. This should fill the little cups almost full. Be sure to also fill the unlabeled cup.
- Take the unlabeled cup and practice adding yogurt to the sodium alginate solution as described in step 4 (but you do not need to weigh your yogurt). It can take some practice to get the hang of it. Once you think you have it, repeat step 4 to create your yogurt test samples.
- Now weigh and start testing your three yogurt samples.
- Put a drop of vegetable oil on a paper towel and wipe the inside of the round tablespoon measuring spoon with the oil on the towel. This will make it easier for the yogurt to slide out of the spoon.
- Place the round tablespoon measuring spoon on the scale and zero out the scale.
- Tip: If the scale you are using does not have a feature to zero it out, weigh the spoon so that you can subtract this mass from the total mass of the spoon and yogurt later.
- Use the round tablespoon measuring spoon to scoop out a spoonful of yogurt. Use the straight edge of a butter knife to make the top of the spoonful flat (this is called making a level spoonful).
- Place the spoon filled with yogurt back on to the scale. Record the mass of the yogurt sample in your data table (under "0 hrs").
- Your first yogurt sample will be sample 1.
- Carefully hold the spoon just above the surface of the sodium alginate solution in the cup labeled "1." Slowly tilt the yogurt into the solution while using a second spoon to help scoop all of the yogurt out of the measuring spoon in one smooth motion (all at once), as shown in Figure 4. The yogurt should form a sphere-like blob in the solution.
Figure 4. Holding the spoon with the yogurt just above the sodium alginate solution's surface, carefully scoop the yogurt out (using a second spoon) so that it stays together as one whole blob in the solution.
- Clean out the measuring spoon and repeat steps 4.a.–4.e. two more times to make a total of three samples. (The second sample will be sample 2 in the data table and go in cup 2, and the third sample will be sample 3 and go in cup 3.)
- Now it is time to take your first weight measurement. This will be the "0" hour time point. Be sure to fill in your data table with your results. Do the following to weigh the yogurt samples:
- Put a piece of plastic wrap on top of the digital scale. (This will protect it from the liquid sodium alginate solution.) Zero out the scale.
- Use a spoon to carefully scoop out the yogurt "ravioli" from the sodium alginate solution in the cup. Hold the ravioli against the side of the cup as you take it out, letting extra solution go back into the cup. Be careful not to pop the ravioli! If you do pop a ravioli, make a note of when it happened in your lab notebook and, if you have time, repeat the Experimental Procedure to create and test additional yogurt ravioli(s).
- Carefully tilt the spoon so that the ravioli slides onto the plastic wrap on the digital scale. Record the mass of the yogurt sample in your data table for the correct time checkpoint.
- Carefully lift the plastic wrap and slide the ravioli back into its cup.
- Repeat steps 5.b.–5.d. for each yogurt sample.
- Put the yogurt samples in the refrigerator (in their cups) and leave them there. Only take the samples out of the refrigerator to weigh them.
- Continue to weigh the yogurt samples at the time checkpoints you decided on (in step 3 of the Preparations section). Be sure to fill in your data table with your results. Also, at each time checkpoint, make observations of how the yogurt samples look. Do they change over time? If so, what changes do you see? Be sure to record your observations in your lab notebook.
- If you have a camera, you may want to also take pictures of your samples over time and/or at the end of your experiment. Later, you could print your pictures and put them on your Science Fair Project Display Board.
Analyzing Your Data
In this part of the science project, you will analyze your data and draw conclusions about how the yogurt raviolis changed over time as they were left in the sodium alginate solution.
- Calculate the average mass of your yogurt samples at each time checkpoint. Record these numbers in your data table (in the "Average" row at the bottom).
- For example, if at the 0 hrs time checkpoint one sample weighed 13.5 g, a second sample weighed 14.2 g, and a third sample weighed 13.7 g, the average mass at the 0 hrs time checkpoint would be 13.8 g (since 13.5 g + 14.2 g + 13.7 g = 41.4 g, and 41.4 g ÷ 3 = 13.8 g).
- Make a line graph of your average mass data over time. Put the time (in hours) on the x-axis (the horizontal axis going across) and put the average mass (in grams) on the y-axis (the vertical axis going up and down).
- You can make a graph by hand or make a graph using a computer program, such as Create a Graph, and print it out.
- Look at your data table, graph, and observations and try to draw conclusions from your results.
- How does the mass of the yogurt raviolis change over time?
- How did spending more time in the sodium alginate solution affect the gel-like layer that formed around the yogurt? Did it get bigger? Did it reach a maximum?
- Can you explain your results in terms of the chemical reaction that is going on in reverse spherification, which is explained in the Introduction in the Background section? Did the chemical reaction stop quickly, or did it continue working for a while?
- Overall, is there a time checkpoint that looked like the "best," or most appealing, yogurt raviolis and why? If you ended up with different types of raviolis (such as with different types of gel-like layers), do you think some would be better in certain food dishes than others?
Ask an Expert
Variations
- Different yogurts can have different amounts of calcium in them. Try repeating this experiment, but use several yogurts with different daily value (DV) percentages of calcium in them. Do you see a difference in how the raviolis change weight over time based on the amount of calcium in the yogurt?
- Repeat this experiment, but this time measure the thickness of the gel-like layer around the yogurt over time. How does it change with time? Tip: You may want to add food coloring to the sodium alginate solution to make it easier to see the gel-like layer.
- Try repeating this science project with other foods that have calcium in them, or add the calcium chloride from the spherification kit to different foods to test. You will want to use gel-like foods, such as yogurt, pudding, or soup. How well do other foods work in reverse spherification? Do their masses change over time?
- How much calcium is needed for reverse spherification to work? To test this, you could repeat this experiment, but instead of using yogurt, you could use distilled water and add increasing amounts of calcium chloride (from the spherification kit) to the water. How much calcium chloride do you need to add for it to form a gel-like substance when added to the sodium alginate solution?
- Use the spherification kit to explore how other foods (ones that do not contain calcium) can be turned into spheres, and how this process is affected by pH, or how acidic or basic a food is. To explore this, check out the Science Buddies project idea Make Popping Boba Balls Out of Your Drinks.
- Investigate how appealing the yogurt raviolis are from different time checkpoints. To do this, repeat this science project, but collect the yogurt raviolis at different time checkpoints, and instead of weighing them, have a group of volunteers judge how appealing the yogurt raviolis are based on their appearance, texture, and possibly taste. (You can read this Science Buddies article about sample size to determine how many volunteers you will need.) Which time checkpoint makes the most appealing yogurt raviolis?
- You could actually use the spherification technique to investigate human biology; specifically, how blood clotting works and how it is affected in people with hemophilia. To explore this, check out the Science Buddies project idea Blood Clotting to the Rescue: How to Stop Too Much Blood from Flowing.
Careers
If you like this project, you might enjoy exploring these related careers:
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