What effect does the type of leavening agent have on biscuits?

Biscuits become light and fluffy as they bake because of ingredients called leavening agents – they produce gas bubbles as dough bakes. They’re what make biscuits rise. Some typical leavening agents include baking soda, baking powder, and combinations of baking soda and vinegar.

This experiment will test the effect of different types of leavening agents on biscuits. There will be four conditions:

  1. No leavening agent
  2. Baking soda
  3. Baking soda and vinegar
  4. Baking powder

To reduce the effects of interactions between leavening agents and other ingredients, I followed a simple biscuit recipe. The recipe, for three biscuits, is as follows:

  • 150 g flour
  • 105 g water
  • 3 g leavening agent

In the case of baking soda and vinegar, I used the same recipe, but with 96 g water and 9 g vinegar.

Each recipe made enough dough for three biscuits. The biscuits were cut using a jar cover, to make each uncooked biscuit a uniform size:

From left to right: unleavened, baking soda, baking soda and vinegar, baking powder.

Observations about the uncooked dough:

Recipe Observations
Unleavened The dough was very sticky. The recipe produced just enough for three biscuits.
Baking Soda This dough was airy, and was easier to roll and cut. There was more dough left over compared to the unleavened recipe.
Baking Soda and Vinegar The dough foamed when the ingredients were added together. The dough didn’t seem as cohesive as the other recipes – it was almost stringy.
Baking powder This seemed to be the lightest or fluffiest of the four recipes. This dough was also stringy, and the most difficult to form into a cohesive disc.

The biscuits were baked at 400 degrees Farenheit for 13 minutes.

The leavening agent seemed to affect the optimum baking time

Recipe Observations Picture
Unleavened These biscuits were soft throughout, and the most dense. It looked to be about the same size and shape as when it went in the oven. It tasted like French bread.  
Baking Soda These biscuits had generally risen more than the unleavened recipe – there were air pockets throughout. These biscuits had  a distinct crust and were on the verge of burning. They left a harsh aftertaste, possibly from too much leavening agent.  
Baking Soda and Vinegar These biscuits had more air pockets than the baking soda recipe, and tasted less harsh. They, like the previous recipe, seemed on the verge of being burnt.  
Baking powder These looked to be the most successful. The dough was cooked throughout, and the outside didn’t appear burnt.  

The experiment was repeated three more times to produce enough data for reliable average heights. Each uncooked biscuit was a disk with a diameter of about 10 cm and a height of 1.3 cm.

Recipe Average Height (cm)
Unleavened  1.4
Baking Soda  2.8
Baking Soda and Vinegar  2.8
Baking powder  2.9

The biscuits were all taste-tested by 5 people after the first round, but that was abandoned for subsequent tests. The recipe sacrificed taste for simplicity, with the biscuits tasting more like French bread than typical biscuits that use lard in the recipe.

In the first taste test, the biscuits with baking soda were found to leave a harsh aftertaste, while the unleavened biscuits tasted under-cooked. The baking powder recipe was the de facto winner.

Conclusion

Of these choices, the type of leavening agent used seemed to have little effect on the height of a cooked biscuit, but substantial effect on the optimum cooking time. This may have to do with the density of the eventual biscuit. The unleavened and baking powder recipes produced denser-looking biscuits than those made with baking soda. The air pockets created with baking soda recipes could have made those biscuits less dense and more sensitive to heat. Further experiments looking at optimum baking time could produce interesting results.

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