itchen science for children on Sunday March 2nd was also excellent!
We focused on Leavenings.
We started off asking the participants if they remembered what we did a week ago.
Finally it was remembered (with a little of my prodding) that we learned about the makeup of the egg and the uses of yolks and whites.
We established that the structure of meringue cookies was constructed by whipping egg whites into a foam. This happens as we use mechanical force to attach air bubbles to the hydrophobic end of the egg white proteins.
We came to describe the process in which air bubbles are used in the formation of baked structures as "leavening".
Then, we discussed other methods of leavening, or generating air bubbles into a dough.
1. Using a living micro-organism called 'yeast' that eats and digests sugars in the flour and 'burps' out carbon dioxide bubbles. The yeast derives its energy from the food it eats and performs a chemical reaction releasing CO2 during digestion. Because it's a living organism, yeast does its best work at ambient or slightly warm temperatures. Put yeast in a hot oven and you kill it. Dead organisms don't eat or burp.
2. Using in inorganic chemical called sodium bi-carbonate, or baking soda. Soda is a base that will react with acids in the dough when water is introduced. The chemical reaction releases CO2 in the form of bubbles into the dough. Because baking soda is not alive, not only does one need to add heat to provide energy for the reaction, adding additional heat accelerates the reaction, sometimes too much. This leavening agent does its best work in a hot oven.
3. Some doughs do not have a great deal of acid in their mix to react well with baking soda. To remedy that, baking soda, the base, is mixed with weak acids like monocalcium phosphate or sodium aluminum sulfate to kick start the leavening reaction. The mixture is called 'baking powder'.
4. One can also leaven using steam, but we do not currently have the equipment that forces steam bubbles into a baking mix.
Using this information, we had a short discussion about the main difference between chametz and matza. Air bubbles, or leavening! The Torah tells us to avoid, on Pesach, baked goods pumped up with air bubbles, or leavened. On the other hand, we are supposed to eat a baked bread with as little possible air in it - matzah. We spent a few minutes on why that might be so.
The participants then designed an experiment using the following variables: Heat level (frigid, ambient, hot), and leavening used (none, yeast, soda, powder)
We formed 4 doughs. 1 with no leavening. 1 with yeast. 1 with baking soda. 1 with baking powder.
We split each dough into 3 pieces. 1 piece of each dough was placed in the refrigerator. Same for an oven warming at about 100F. Same for an oven at 350F.
Therefore, there were 4 pieces of dough representing each of the 4 leavening choices in either the fridge, the ambient oven and the hot oven.
While the participants observed the doughs through the windows of the toaster ovens, they worked on making 'matzahs' - pounding the dough flat, making holes with a fork and placing into a hot oven.
then we took some time to predict what we will expect to find. During this discussion, the participants volunteered that rising time and baking time were important variables, just like the leavening chosen and the temperature at which to leaven the dough.
After about a half hour we removed placed all the doughs in front of us on a table and compared and contrasted, size and shape. We then cut them open and described what we found. All the while attempting to explain the differences noted among the doughs.
Of course, we said Hamotzi on our matza and had that as a snack while we discussed our results!
We then reviewed and summarized what we learned, sang birkat hamazon together and adjourned.
They had a great time.
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