Chemical Leaveners in Muffins

In the last post, we explored the roles of baking powder in muffins by taking it out of a recipe and then by adding in extra. Today, we’re going to continue experimenting with leaveners in muffins, but now we’re going to add baking soda into the mix. We discussed the differences between baking soda and baking powder in a previous post, but now we’ll see how these differences play out in a baked good.

Experiment Overview

Goal: To see and taste differences in structure, texture, and color in muffins with different chemical leaveners
Recipe: Best Ever Muffins from AllRecipes
Method: Mix and divide the dry ingredients except for the leavener. Add baking powder, baking soda, or baking soda and cream of tartar. Add the wet ingredients to each batch of dry ingredients. Bake, cool, and taste.
Results: Among the three types of muffins, we noticed differences in
– Batter density
– Shape and height
– Taste
– Color
– Texture
Conclusions: Baking powder cannot be replaced with just baking soda. In muffins, baking powder can be substituted with a combination of baking soda and an acid, but the muffins will have a different shape and texture.

Testing Method

Ingredients and Equipment

  • 2 c (250 g) Baker’s Corner bleached all-purpose flour
  • 1/2 tsp Stonemill iodized salt
  • 3/4 c (150 g) sugar
  • 1 tsp Baker’s Corner double-acting baking powder
  • 1/2 tsp Arm & Hammer baking soda, divided
  • 1/2 tsp McCormick cream of tartar
  • 1 c (238 g) Friendly Farms Vitamin D whole milk
  • 1 Goldhen large egg, beaten
  • 1/4 c (61 g) Carlini vegetable oil
  • Whisk
  • Rubber spatula
  • 12-cup muffin pan lined with cupcake liners

Baking the muffins

  1. Preheat oven to 400°F.
  2. Whisk the flour, salt, and sugar together in a large bowl (404g total). Divide into three portions (134g each). To each portion, add 1 tsp baking powder (control), 1/4 tsp baking soda (BS), or 1/4 baking soda and 1/2 tsp cream of tartar (BS+CT). Whisk well to combine.
  3. In a separate bowl, whisk the milk, egg, and vegetable oil together (351g total). Pour one-third (117g) of the wet ingredients into each portion of dry ingredients. Fold the wet and dry ingredients together until just combined.
  4. Divide each portion of batter into four muffin cups.
  5. Bake for 21 minutes. Cool on a wire rack for 5 minutes, then remove muffins from pan to cool completely.

Results

To better understand some of these results, I suggest reading through the last few posts about leavening, especially the one about chemical leaveners. Remember that baking powder is a mixture of baking soda, acid salts, and cornstarch. The baking powder I used contains the slow-acting acid salt sodium aluminum sulfate (SAS) and the fast-acting acid salt monocalcium phosphate (MCP). Cream of tartar, which I used in the BS+CT muffins, is a fast-acting acid salt.

For the BS and BS+CT muffins, I replaced every teaspoon of baking powder in the control muffins with a quarter teaspoon of baking soda since baking soda has one-quarter of the leavening power. In the BS+CT muffins, I also added half a teaspoon of cream of tartar, enough to react with all of the baking soda. Other acids that I could have used in place of cream of tartar are lemon juice and vinegar, which I would have added to the wet ingredients.

Batter density

The muffin batter with both baking soda and cream of tartar (BS+CT) was noticeably airier than the other two batters. When I divided the batter into the muffin pan, the BS+CT muffins also had significantly more volume. When we combine the liquid and dry ingredients in the BS+CT batter, all of the baking soda and cream of tartar dissolve in the water from the milk and egg. Once dissolved, they react and produce carbon dioxide gas. The carbon dioxide enlarges existing air bubbles we’ve mixed into the batter, lightening it and adding volume.

In the muffins with just baking soda (BS), the baking soda dissolves, but there isn’t an acidic ingredient in the batter. Without acid, the baking soda can’t react to produce carbon dioxide, so it just sits dissolved in the water. As a result, the BS batter doesn’t contain much carbon dioxide, and its volume doesn’t change much.

Similarly, in the baking powder muffins (control), not much carbon dioxide is made when we combine the liquid and dry ingredients. The baking soda within the baking powder dissolves, as does the acid salt MCP. They react and produce carbon dioxide, but there’s not enough MCP to react with all the baking soda. After the MCP is used up, the remaining baking soda has no more acid to react with, so like in the BS muffins, it remains dissolved in the water, unable to do much else. Since baking powder produces less leavening gas at room temperature, the control batter is denser than the BS+CT batter.

Shape and height

Once the control muffin batter starts to warm up in the oven, though, the other acid salt in the baking powder, SAS, dissolves. Once dissolved, it reacts with the remaining baking soda to produce more carbon dioxide. In both the control and the BS+CT muffins, the carbon dioxide expands and the muffin rises. Thus, even though the BS+CT muffins start with more volume, they and the control muffins end up with a similar amount of carbon dioxide and a similar volume.

However, notice the difference in the surfaces of the two muffins in the photo above. While the control muffins are craggy and rough, the BS+CT muffins are smooth. This is a result of the early carbon dioxide production in the BS+CT muffins. In the control muffins, carbon dioxide is still expanding the inside of the muffin as the top crust sets. The crust fractures to accommodate the increasing volume of the muffin, forming cracks. However, in the BS+CT muffins, all of the carbon dioxide is created before the muffins even enter the oven. As a result, it reaches its full volume more quickly (the image below was taken about eight minutes into baking), and by the time the outer crust sets, the inside of the muffin is pretty much done rising, too. As a result, the top crust remains intact and the surface is smooth.

How about the muffins with only baking soda? Notice that they never rise as high as the others. A lot of the baking soda’s leavening potential was lost because it didn’t have enough acid to react with. So how did it provide any leavening at all? The baking soda may have reacted with the few acid molecules it did find within the muffin batter to produce a minimal amount of carbon dioxide. And baking soda can actually produce carbon dioxide without acids if it reaches high enough temperatures. The atoms in the baking soda just separate into several compounds including carbon dioxide.

However, bakers don’t use baking soda this way for a few reasons. First, it produces much less carbon dioxide, as you can see from the muffins’ low volume. Second, when baking soda decomposes, it also forms a salt that tastes like soap. And third, by the time the muffin gets hot enough for the baking soda to decompose, its structure has already become too rigid for the muffins to be leavened effectively. If the batter can’t expand, there’s no point in pumping extra gas into it. As you can see in the cross-sections below, the BS muffins are littered with tunnels, similar to the ones we saw in the overmixed muffins. This suggests that most of the carbon dioxide gas formed after the batter solidified, then increased the pressure in its air bubble until it burst up through the batter, leaving a tunnel in its wake. Another way we can tell that the carbon dioxide was produced too late is the sharp peaks on the BS muffins. These peaks suggest that by the time the batter contained enough carbon dioxide to expand, the outsides of the muffin had already set. As a result, only the cooler batter toward the center of the muffin rose.

Color

Another striking difference among the muffins is in their color. The baking soda muffins were much darker than the others, both on the crust and inside. Browning occurs via two processes: the caramelization of sugar and the chemical reaction of sugars with proteins in the Maillard reaction. The rates of both of these reactions are influenced by pH, a measure of acidity and basicity.

Baking soda is a basic salt, so when it dissolved in the BS muffin batter, it increased the batter’s basicity. Without much acid to neutralize it, the baking soda raised the pH of the batter. In basic (or alkaline) environments, both caramelization and the Maillard reaction proceed more quickly. (Read more about the effect of pH on these chemical reactions here.)

There’s also a brown streak in the baking soda muffin. Muffin batters are supposed to be lumpy to minimize gluten development. The streak was a chunk of dry ingredients including baking soda. Because that area contained a higher concentration of baking soda, it was even more basic than the surrounding batter, so it turned even browner.

In contrast, in both the control and BS+CT muffins, the baking soda was neutralized by acids either already contained in the baking powder or added by us. As a result, the baking soda did not significantly change the pH of the batter, and the rate of the browning reactions and the final color were similar.

Taste

Given the many indicators that there was something wrong with the BS muffins, it is probably unsurprising that they did not taste good. The chemical taste of the baking soda was not overwhelming (as it was in these cookies), but it was noticeable. The other muffins, the control and the BS+CT, tasted quite similar and did not have a noticeable chemical aftertaste. Although baking soda reactions with acid do produce salts with flavors, the salts are present only in small quantities, enough to complement but not to overpower.

Texture

Since the baking soda in the BS muffins did not release their full leavening potential, these muffins were chewier than the others. When gases expand in the oven, they stretch the batter around them to tenderize the baked good. With less carbon dioxide, the BS batter remained underleavened and dense.

Both the other muffins had a good texture. One taster preferred the control, and the other preferred the BS+CT. Although they enjoyed both the muffins, there was a noticeable difference in their textures. The control was slightly fluffier, and it felt like my teeth squished the muffin when I bit into it. The BS+CT was a tad denser, and my teeth sliced through it more easily.

Conclusions

Baking powder is typically used in muffins because there aren’t many acidic ingredients. We can substitute the baking powder with baking soda and an acid, but because the carbon dioxide is released early, the bake turns out a little differently. In addition, we have to be much more cognizant of how quickly we move. If the batter sits out for too long, the carbon dioxide will diffuse out of the batter and we will lose leavening power.



References

Corriher, S. O. Bakewise; Scribner: New York, 2008.

Figoni, P. How Baking Works, 3rd ed.; John Wiley & Sons, Inc.: Hoboken, 2011.

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