Figure 2.2 Apparatus for collecting and quantifying the volume of gas released.
2.5.1.2 Experimental Treatments and Controls
Note: When there is more than one ingredient, mix them together thoroughly before adding to the flask.
1 Control (no leavening agent)
2 Sodium bicarbonate (0.34 g)
3 Sodium bicarbonate (0.34 g) + MCP‐H2O (0.42 g)
4 Sodium bicarbonate (0.34 g) + SAS (0.33 g)
5 Baking powder (1.21 g). Note: this assumes that baking powder is 28% NaHCO3.
2.5.1.3 Protocol
Note: This is a standard protocol for measuring leavening rates in a model system.
1 Add 60 ml distilled water and a magnetic stir bar to a filter flask.
2 Fill a 100 ml graduated cylinder with tap water and invert it in a pan of water as shown in Figure 2.2 (take care to avoid allowing air to get into the cylinder).
3 Weigh out the specified amounts of each of the leavening agents (see Section 2.5.1.2).
4 With the stirrer running on low speed, transfer the leavening agent to the flask and stopper immediately. (Note: The rate of stirring will affect the rate of the reaction, so always use the same setting on the stirrer.)
5 Record the volume of displaced water in the cylinder every 30 seconds for five minutes.
6 Now, set the flask in a water bath held at 65 °C and continue recording the volume for an additional five minutes. (Note: Temperature can have a marked effect on CO2 generation, so regulate the temperature carefully.)
7 Measure the final pH of the solution in the filter flask.
2.5.1.4 Data Analysis
Note: A spreadsheet program will save you time on this exercise.
1 For each data point, subtract the control value from the treatment value.
2 Determine the total available CO2 in each of the treatments (express as moles of CO2). Assume that the baking powder contains 28% sodium bicarbonate.
3 Determine the moles of CO2 evolved at each time point. (You will need to use the ideal gas law to calculate the moles of CO2.) Transform your data to % of total available CO2.
4 Plot %CO2 evolved vs time for each of the treatments. Your plot should be similar to Figure 2.1. Be sure to indicate on your plot the point where you put the flask into the 65 °C bath.
2.5.2 Chemically Leavened Biscuits
2.5.2.1 Biscuit Formula
| Ingredients | Amount |
|---|---|
| All‐purpose flour | 100 g |
| Sugar | 6 g |
| Sodium bicarbonate | 1 g |
| Leavening acid | To be calculateda |
| Salt | 1.5 g |
| Oil | 23 g |
| Skim milk | 80 ml |
a Use the appropriate neutralizing values to calculate the amount.
Source: Adapted from [11].
2.5.2.2 Treatments
1 Control 1 (no leavening acid and no sodium bicarbonate)
2 Control 2 (1 g sodium bicarbonate but no leavening acid)
3 Fast‐acting leavening acid (use monocalcium phosphate monohydrate)
4 Slow‐acting leavening acid (use sodium aluminum sulfate)
5 Double‐acting leavening acid (use a 50 : 50 mixture of MCP monohydrate and SAS).
6 Baking powder (3.8 g), no sodium bicarbonate.
2.5.2.3 Protocol
1 Mix the dry ingredients thoroughly in a mixing bowl.
2 Add the milk, and oil and mix thoroughly (use 16 strokes) with a rubber spatula.
3 Measure out 65 g aliquots of the dough and place on a baking sheet. Make sure there is 1‐inch separation between each biscuit.
4 Bake at 218 °C (420 °F) for 15 minutes.
5 Cool down.
6 Compare volumes (see below) and textures of the various treatments.
7 Calculate the density of each biscuit.
2.5.2.4 Volume Determination of Biscuits
1 Select a plastic container (e.g. margarine tub or yogurt carton) slightly larger than the biscuit.
2 Fill the container level full with fine seeds (rapeseed or millet).
3 Pour seeds in the container into a graduated cylinder and record volume.
4 Place the biscuit in the empty container and refill with seeds.
5 Measure the volume of the seeds and calculate the volume of the biscuit by difference.
2.6 Problem Set
Note: These problems are designed to help you review concepts from introductory chemistry. Consult your introductory chemistry textbook for review.
1 Calculate the volume (at 25 °C and 1 atmosphere) of available CO2 contained in 0.34 g NaHCO3.
2 Explain why leavening rates differ between leavening acids.
3 The bicarbonate ion contains a proton and yet bicarbonate acts as a base in most leavening systems.
