Abstract

Objective

The objective of this food science fair project is to investigate how the rate of cooling affects crystal structure.

Introduction

Did you know that there are around 300 different natural flavor compounds in pure maple syrup? Other prominent ingredients are sugar, caramel, and vanilla. Nutty, buttery, floral (honey), cereal, chocolate, and coffee flavors can be found in some syrups! As is the case for most natural products, maple syrups have complex flavor chemistry to delight your senses of taste and smell.

Chemically speaking, maple syrup is a concentrated solution of sugar in water, with many minor flavoring compounds. When it is heated, some of the water evaporates off and the sugar becomes more concentrated. As the heated maple syrup cools, the sugar molecules (the smallest particles of the sugar) form crystals. Unlike the sugar molecules in liquid syrup, which are free to float around, sugar molecules in the heated, concentrated syrup form these crystals, which line up and arrange themselves in an orderly and repetitive pattern. So as the water evaporates, the sugar molecules bump into one another frequently because there are so many of them, so close together. Occasionally, when they bump into each other, the molecules end up sticking together. This slow process is how the crystal "grows."

You might think of a growing crystal as a big block of Legos. Each individual Lego is like a sugar molecule, because it is the smallest "piece" possible. When you add a new Lego piece to the big block, you have to line it up just right so that it will fit in with the pieces that are already there. In the same way, sugar molecules have to align themselves just right in order to become part of the growing crystal.

Crystals can form at different rates; for instance, snowflakes form in seconds, but amethysts and rubies form over years. As you might imagine, the final crystal shape is affected by how fast the molecules adhere to the growing crystal. The slower the rate, the more time each molecule has to get aligned with its neighbors, resulting in a more organized final crystal. In this cooking and food science fair project, you will study how the rate of crystal formation affects crystal shape in maple syrup.

Terms, Concepts, and Questions to Start Background Research

• Solution
• Evaporation
• Concentration
• Molecule
• Crystal
• Sucrose
• Glucose
• Fructose
• Viscous

Questions

• What makes crystals different from other solid materials?
• What are the differences between imitation maple syrup and pure maple syrup?
• What is the definition of the chemical term precipitation?
• Why do crystals form after you heat the syrup, but not in unheated syrup?
• Based on your research, list some examples of how the rate of cooling affects crystal growth in different materials.
• What other kinds of food are in the form of crystals?

Bibliography

• MacDonald, A. (2005, May 23). Maple Sugar Crystal Candy. Retrieved November 12, 2008, from: http://www.googobits.com/articles/p2-59-kitchen-science-for-kids.html
• Cornell Sugar Maple Research & Extension Program. (n.d.). Maple Syrup FAQs. Retrieved November 12, 2008, from http://maple.dnr.cornell.edu/FAQ.htm

Materials and Equipment

• Small baking pan filled with a thin layer of water and frozen to create a flat sheet of ice
• Pure maple syrup (not the imitation syrup)
• Saucepan
• Large spoon
• A second small baking pan at room temperature
• Stopwatch
• Lab notebook
• Ruler
• An adult helper

Experimental Procedure

1. Before you heat the maple syrup, make a sheet of ice by placing a thin layer of water in a baking pan and keeping it in the freezer until it is frozen solid.
2. Once the water in the baking pan is frozen, heat the maple syrup over medium heat in the saucepan, stirring constantly. Note: You will need the help of an adult for this part.
3. Bring it to a boil and allow it to cook, uncovered, until it is very thick and viscous. Keep stirring to make sure that it does not burn.
4. Set out the baking pan with the sheet of ice on the countertop.
5. On another flat area of the counter, set out the other room-temperature baking pan.
6. Use your spoon to drop one dollop of the hot, thick maple syrup onto the ice or onto the room-temperature baking pan. You might want to drop the dollop on the frozen baking sheet first, before the ice melts.
7. Do not touch the dollop yet—it will still be really hot!
8. Watch as the maple syrup cools. Use a stopwatch to time how long it takes for crystals to form and solidify on the dollop.
9. Observe the shape and measure the length of the crystals. Use a magnifying glass to get a close look at the crystals.
10. Record your observations about how long it took for the crystals to form and how the rate of cooling affected their size in your lab notebook. Use a data table like the one below. Remember, your notes and observations should be clear enough that someone else could use them to reproduce your results.

11. Repeat steps 6-9 until you have observed at least three dollops on each baking sheet. If your first dollop was on the frozen baking sheet, you might want to drop your next two dollops there, too, before the ice melts. However, if it does start to melt, simply refreeze it and you can continue with your trials on the room-temperature baking sheet.

Variations

• Experiment with the sugar concentration before you put the dollops on ice by heating the solution for different amounts of time. Can you think of some ways to figure out how much you have reduced the volume of the syrup?
• Experiment with cooling the syrup very slowly. For example, allow the syrup to cool in an insulated cup. Are crystals that are made very slowly different than the ones you made earlier?
• What happens if you form the crystals in the refrigerator?
• For another science fair project about sugar, try the Science Buddies science fair project When Science is Sweet: Growing Rock Candy Crystals.

• For more science project ideas in this area of science, see Cooking & Food Science Project Ideas.

Credits

David Whyte, PhD, Science Buddies

Last edit date: 2008-12-10 12:29:00