ACS ChemClub 2015 Virtual Party Resource Packet
Chemistry—Hacking Your Taste Buds
Chocolate Chip Changes
Student Handout
A fun way to “hack” the properties of a chocolate chip is to change the crystalline structure of the cocoa butter in the chocolate. When chocolate cools in an uncontrolled way, the fat molecules form unstable crystals. When chocolate cools in a controlled way by keeping it at a set temperature and seeding it with tempered chocolate, the fat molecules form tightly packed, stable crystals. In this activity, you’ll compare chocolate chips that have been cooled in uncontrolled and controlled ways.
But first, you need to translate the “science speak” of the Theobroma cacao chip (chocolate chip!) cookie recipe below. What are the ingredients you need to gather?
Materials
· 315 g of a blend of hard and soft flours
· 5 mL sodium hydrogen carbonate
· 5 mL sodium chloride
· 200 g partially hydrogenated soybean and cottonseed oils, mono and diglycerides (Or, 220 g softened unsalted butter)
· 200 g refined crystalline sucrose
· 200 g unrefined, light, crystalline sucrose
· 10 mL pure vanilla extract
· 2 matured ova (~50 g each) with yolk overlaid with albumen proteins from Gallus domesticus female, at room temperature
· 340 g Theobroma cacao chips (set aside several chips for the second part of the activity)
· Oven
· Oven mitts
· Mixing spoon or mixer
· 2 bowls (medium-sized and large-sized)
· Sifter
· Cookie sheet
· Parchment paper (preferred) or aluminum foil
· Metal spatula
· Cooling rack
Activity
This activity must be done in a food-safe environment rather than a chemistry laboratory, since participants will be eating and tasting food products. Students with food allergies should confirm they are able to safely perform this experiment with the foods used.
A. Cookies
1. Preheat oven to 460 Kelvin.
2. In a medium-sized bowl, sift together the blend of hard and soft flours, sodium hydrogen carbonate, and sodium chloride.
3. In a large-sized bowl, stir together the partially hydrogenated soybean and cottonseed oils, mono and diglycerides (or softened unsalted butter) and both kinds of crystalline sucrose. Mix until fluffy.
4. Add the vanilla extract and stir.
5. Add the ova one at a time, stirring ~30 s between each addition.
6. Add the sifted mixture and gently stir to incorporate the dry reactants.
7. Add the Theobroma cacao chips (set aside several chips to use in Part B).
8. Form balls of the mixture. Place them on a cookie sheet lined with parchment paper (preferred) or aluminum foil.
9. Place the cookie sheet into the preheated oven for 10–12 min. or until they are golden-brown.
10. Carefully remove the cookie sheet using an oven mitt. Place on a heat-protected surface and cool for several min. Then, use a metal spatula to move the cookies to a cooling rack. Repeat steps 8 through 10 until the dough is used up.
B. Chocolate Chip Changes
1. Place one of the unbaked chocolate chips that you set aside in Part A in your hand. Does it melt from the heat of your hand? Can you easily compress it with your fingers?
2. Place the chip in your mouth. Allow it to sit on your tongue. Does it melt from the heat of your mouth?
3. Move the chip around your tongue and taste it.
4. Choose a baked chocolate chip cookie from Part A that has already cooled to room temperature. Touch one of the chocolate chips on the surface of the cookie or break it in half to find a chip. Touch it with your hand. Can you easily compress it with your fingers?
5. Place the chip in your mouth. Allow it to sit on your tongue. Does it melt from the heat of your mouth?
6. Move the chip around your tongue and taste it. Does it taste different than the unbaked chip?
Questions
1. Compare the physical properties of the unbaked and baked chocolate chips.
2. Compare the taste of the unbaked and baked chocolate chips.
3. The unbaked chocolate chips are tempered, while the baked are untempered. What effects does tempering have on the chocolate?
Take a Look!
· ACS Reactions video “How to Cookie with Science” https://www.youtube.com/watch?v=3b4shT7EBZQ
· ACS Bytesize Science video “Five ‘Sweet’ Facts About the Chemistry of Chocolate”
https://www.youtube.com/watch?v=GC3QAXJogQQ
(all URLs accessed October 2015)
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Lab–Student: Chocolate Changes, pg