Activity 3: Confectionery Chemistry, Round 3 – Juice Infused Chocolate
For the Teacher: This will be one of the summative assessments for the unit. After having learned to identify mixtures and their homogenous and heterogeneous components, students will now create homogenous chocolate infused with fruit juice. So that time is not wasted, it is important to have many of the materials prepped in advance. Also, having access to two microwave ovens will speed up this process and reduce student idleness. Once the confectionaries have been cooled, invite 3-4 teachers to class to help judge the final competition.
For the Student: Welcome to the final round of Confectionery Chemistry! In this round, you will take your juice extract from round 2 and combine it with chocolate to create a juice-containing chocolate confectionary. The goal is to infuse a fruity flavor into the chocolate, maintain the structural integrity of your treat, and ultimately, reduce the fat content of the chocolate by 40%! In the competition, you must use an electronic device to vlog your progress, which will be compiled into a YouTube video.
Materials
- Ascorbic Acid Solution Stock: Dissolve a 2.12 grams (1/2 tsp) of L-ascorbic acid powder in 240 mL (1 cup) of water for a concentration of ~0.05 M and a pH of 3.15.
- Chitosan Powder: When mixing chocolate with liquid, the expectation is that the chocolate will get softer and acquire a lower melting point. However, the chitosan acts as an emulsifier to trap juice in droplets and also preserve the structural integrity of chocolate.
- Preparation of Juice: Heat 79 mL (1/3 cup) of beverage to 40 °C. Measure 1.4 grams (1/2 tsp) of chitosan. Thoroughly agitate by shaking in a closed container or a drink mixer. To assist with dissolving the chitosan and maintaining a native pH, add 15 mL (1 tbsp) of the L-ascorbic acid solution.
- Baker’s Chocolate: In order to see a noticeable difference, a chocolate with high fat content must be used. Hershey’s Semi-Sweet Cooking Chocolate bar is great choice to start with. Each piece weighs about 14 grams and contains 4 grams of fat, which is ~30% of the whole bar. Each student group should get about 50 g of chocolate to work with. Using the aforementioned chocolate bar, that is 4 squares of chocolate totaling 56 grams, containing 16 grams of fat. If using a different chocolate, it is vitally important to note how much fat is actually present per serving of chocolate.
- Drink mixer or frother: The juice being infused into the chocolate needs to be mixed evenly. A drink mixer, such as the Matcha DNA mixer, is a small and inexpensive device. It is needed in two stages: to mix the chitosan with the juice concentrate and L-ascorbic acid and to mix the juice into the chocolate. You should demonstrate this with the students because it can get rather messy. Mixing the juice will create a lot of froth, while mixing the chocolate requires more patience as the mixer will actually reduce in speed when it comes into contact with the chocolate.
- Microwave oven (adjustable power of ~700 watts and lower): The key to preventing the chocolate from burning is to heat the chocolate at a low power setting in the microwave oven. Since the chocolate will not be in the presence of a solvent, it needs to be heated at ~700 watts to start the melting process quickly. Once the chocolate is actually melted, it must be reheated in the microwave oven at lower powers (~250 watts). Chocolate melts with the assistance of human body heat. Therefore, in order to melt the chocolate without burning it, the temperature must not exceed 46°C or 115°F.
Procedure: Preparing chocolate emulsions
Remove the chocolate from the microwave oven. Melted chocolate is very viscous and you may be unable to tell if it is melted until you perturb it with a mixer. Use the handheld drink mixer or milk frother to assist in stirring the chocolate. The key to keeping the chocolate intact is heating it for short periods of time and at a lower power without burning it. Once the chocolate is actually melted, it must be reheated in the microwave oven at lower powers (~250 watts).
Once the chocolate is melted, add the fruit juice containing chitosan and mix using a drink mixer. The fat content of your chocolate becomes important here. For example, if you are using 56 grams of chocolate, as previously suggested, then there is 16 grams of fat present. The recipe requires a ratio of juice emulsion equal to that of the fat content. Therefore, students will need to add roughly 15-16 mL of juice. The assumption is that most juices have a density slightly greater than 1.0 g/mL. After mixing, close the container and allow the chocolate emulsion to rest for 10 minutes. Then store in the refrigerator.
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