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Comparing Cranberry Condiments

Summary

Active Time
45 minutes to 1 hour
Total Project Time
Up to 1 day
Key Concepts
Polymer, pectin
Credits
Teisha Rowland, PhD, Science Buddies
Sabine De Brabandere, PhD, Science Buddies
Cranberry jelly and raw cranberries

Introduction

Does your family have jellied cranberry sauce with Thanksgiving dinner? Jellied cranberries are thick and retain the shape of the mold in which they are placed, which might mean a turkey-shaped mold or even the shape of the can if you use a canned version. Taking a bite of jiggly jellied cranberries can be a fun addition to a delicious meal, but cranberries can also be served as a liquid-like sauce. Both versions use the same ingredients, so what makes one turn into a gelatin while the other stays more fluid? To find out, try out this holiday-flavored science activity!

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Materials

  • Two 12-ounce bags of fresh or frozen whole cranberries
  • Colander
  • Two cups of granulated white sugar
  • Water
  • Measuring cup
  • Pot, at least four-quart capacity
  • Heat-resistant, long-handled spoon for mixing on the stove
  • Stove
  • Candy thermometer or digital thermometer that can withstand temperatures of at least 310° F or 154° C (It is recommended to use one that comes with a clip to attach it to the side of the pot.)
  • Watch or timer
  • Ladle
  • Four ramekins or other small, heat-resistant containers, such as mugs or a muffin tin (They should each hold at least three quarters of a cup, and be the same size and shape.)
  • Butter knife and plates (optional)

Prep Work

  1. If you are using frozen cranberries, thaw them in advance.
  2. For fresh berries, pour cranberries into a colander. Rinse the cranberries, throwing away any that are squishy rather than firm. Drain thoroughly and set them aside.

  3. Make sure an adult helps with making the cranberry samples on the stove. When it is on the stove, the cranberry mixture will be very hot and prone to splattering. Be cautious when stirring—if the mixture gets on your skin, it could burn.

Instructions

  1. Add two cups of water and two cups of sugar to the pot. If you are using a candy thermometer with a clip, attach the thermometer to the side of the pot.
  2. Heat the pot on a stovetop burner, adjusting the burner to medium-high heat. Stir the water and sugar mixture until all the sugar is dissolved.

  3. Add the cranberries and stir occasionally. After a couple of minutes, the cranberries should start popping open.
    Think about:
    What does the popping of berries sound and look like?

  4. Keep stirring until you can count slowly to five without hearing another cranberry pop open.
    Think about:
    What is the temperature of the mixture?
  5. If the temperature is below about 212° Fahrenheit, continue stirring and monitoring the temperature. You will need to keep stirring the mixture almost continuously, and you may need to turn the heat up to high to reach the 212° F (100° C) mark. (Note: Water that is much above sea level boils at a lower temperature, such as at about 203° F at an elevation of one mile. Consequently, if you live at a high elevation, your mixture might not reach 212° F and you should aim for a slightly lower temperature.)

  6. Start the timer once the temperature reaches about 212° F (or the equivalent for your elevation).
  7. Observe when the timer indicates three minutes.
    Think about:
    How do the cranberries look? Are they mostly whole, completely unrecognizable from the rest of the sauce, or somewhere in between?
  8. Scoop out one ladle full of cranberry mixture and carefully pour it in a ramekin (or other small, heat-resistant container).
    Think about:
    What is the consistency of the mixture you scooped out?
  9. Let the timer run while you continue stirring, and observing the cranberry mixture. Remove another full ladle of cranberry mixture when seven minutes have passed since you stared the timer. Pour it into a separate ramekin.
    Think about:
    How do the cranberries look now? What is the mixture's consistency like?
  10. In the same way, remove a full ladle of cranberry mixture at 11 minutes and another at 15 minutes, putting each scoop into their own ramekin.
    Think about:
    How do the cranberries look after 15 minutes of cooking compared with three minutes? How did the consistency of the cranberry mixture change over time as it was cooked? How do the colors of the mixtures compare with one another? Do you see a pattern or a relationship between these observations and how long the cranberries were cooked?

  11. Optional: Let the cranberry sauce samples cool at least two hours at room temperature. After they have cooled, unmold each sample onto a fresh plate by running a butter knife along the inside edges of the ramekin or container to gently loosen the cranberry mixture, placing a plate face down on top of the ramekin and then flipping over the ramekin and plate together.
    Think about:
    What is the color and consistency of the different samples once they have cooled? How do they compare with one another? Do any of them retain the molded shape of the ramekin, which means they are considered to be jellied cranberry sauce?

Cleanup

You may enjoy a tasty snack of cranberry sauce! Do not forget to clean your work area and utensils with soapy water and put everything back where it belongs.

What Happened?

Did the cranberry mixture that was cooked for the shortest amount of time make a relatively runny, liquidlike cranberry sauce with whole cranberries still visible? Did the one that was cooked the longest make the thickest and firmest jellied cranberry sauce?

Cranberries contain pectin, a natural substance that gives the berries firmness and structure. The longer the cranberries are heated in a hot liquid, the more they break apart, which releases more and more pectin into the water. With added heat and sugar, the pectin polymers bind to one another, giving the mixture structure and firmness. In addition, water is released as steam while you cook the cranberries, which means that the longer they cook, the less water the sauce holds. Taken together, this is why cranberry sauce that is cooked longer becomes thicker and has fewer whole cranberries visible. It is also the firmest, thereby retaining its shape the best once cooled.

As you should have seen in this activity, jellied cranberry sauce (which retains its shape) can be made by cooking fluid cranberry sauce for a longer amount of time.

Digging Deeper

Cranberry sauce can be served either as a gooey liquid or as a solid jelly. The jellied version is solid enough to retain the shape of the container in which it is placed, while the sauce version is much more fluid. The difference between the fluid sauce and the jelly versions comes down to pectin.

Pectin is a natural polymer—a series of molecules that attach to one another to form long chains. It is found in nature between plant cells and within their cell walls. Pectin helps "glue" the plant cells together, keeping their tissues firm.

When cooked under the right conditions, pectin polymers tangle and interact, forming a net that traps dissolved sugar, so the sugar and water molecules cannot flow. This creates a firm shape: a gel. It is pectin that helps stick the cooked fruit together to form a solid jelly in cooked cranberries as well as in other fruit jams and jellies.

Cranberries naturally contain a lot of pectin, which helps keep the berries nice and firm. This pectin gets released when they are cooked and is vital in forming the gel when cooled. Some other factors play a role too: cook it for too short a time, and not enough pectin is released; do not add enough heat or sugar, and the pectin cannot do its work either.

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For Further Exploration

  • Sugar plays an important part in allowing pectin molecules to find one another when cooking cranberries. To investigate this, try this activity again, but this time try increasing or decreasing the amount of sugar you use. What happens to the cranberry sauce's ability to solidify as you change the amount of sugar in the recipe? Hint: If you are having trouble interpreting your results, you might also want to think about how sugar affects the boiling point of water.
  • Try this activity with other fruits. Can you find other fruits that have enough natural pectin to create solid gels?

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