The main chemical interaction happening in this scones recipe is the chemical leavening caused by the baking powder and baking soda. This interaction is what causes the dough to rise, creating the scones’ airy texture.
Baking soda, also known as sodium bicarbonate, is a pure compound, and it cannot react unless there is an acid present in the recipe and both ingredients are water. In this recipe, the sour cream is the acid and the water mostly comes from the eggs and the sour cream itself.
Baking powder is a mixture which includes baking soda and two different acids, one of which reacts as soon as the baking powder comes into contact with water, and one which reacts later while the scones are baking, This is why baking powder available in stores is called double-acting baking powder.
Based on the conditions required for baking soda and baking powder to react, they should both be able to do so independently in this scones recipe, which led me to wonder why the recipe called for both of them. I decided to try making three batches of scones. The first batch would be my original recipe halved, the second would substitute 1 tsp baking powder instead of the baking soda, and the third one would substitute 1/4 tsp baking soda for the baking powder. I could then compare the three batches and see what changed.
From my initial research, I knew that the main reason baking powder and baking soda were both included in many recipes was to allow for a second reaction that only the baking powder could cause, based on this, I guessed that the baking soda only scones wouldn’t rise as well as the other two batches, but I didn’t expect to see any major changes in the baking powder only scones compared to the original recipe.
First batch: Original recipe
The original batch turned out fairly well, they looked very similar to how they always did when my mom made them, and they tasted very similar too, although I may have used a little bit less sugar than I should’ve. They rose well and had a light color on the inside.
Second batch: Baking Powder only
This batch turned out almost identically to the original batch, they had a very similar color on the outside and inside, and they didn’t taste noticeably different to me, though I was dealing with allergies at the time so my sense of smell was not particularly acute. They also rose to a similar height as the original batch.
Third batch: Baking Soda only
This batch had a significantly different outcome. It rose slightly less than the other two batches, but it had significantly more browning on the outisde (likely due to the increased alkalinity of the baking soda compared to the baking powder), and it had a much darker color on the inside. It was clearly much denser on the inside, and had a darker color. It tasted very different, a bit closer to corn bread.
Conclusion: After this experiment, my conclusion is that the benefit of having both baking soda and baking powder in a recipe is that the baking powder reacts twice, allowing the dough to rise well, and the baking soda provides a stronger initial reaction and increases browning. Baking powder can be substituted for baking soda without ruining a recipe, but baking soda cannot be substituted for baking powder.
Potter, J. Cooking for Geeks; O’Reilly Media, 2010; pp 239-251.
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