Overmixing Muffins

Muffin recipes often instruct, “Mix until just combined.” Some even caution, “Do not overmix. Batter will be lumpy.” Bakers characterize overmixed muffins as dense, chewy, tough, or stringy due to excessive gluten development, but we wanted to see if we could taste the difference ourselves.

Experiment Overview

Goal: To see and taste a difference in muffin textures as the batter is mixed more and more
Recipe: Best Ever Muffins from AllRecipes
Method: Prepare one batch of muffin batter. Fill a couple muffin cups, then mix the remaining batter some more. Fill a couple more muffin cups, then continue mixing the remaining batter. Repeat until all muffin cups are full. Bake all muffins, cool, and taste.
Results: As the batter was mixed for longer, we noticed
– Smoother, runnier batter
– Smoother muffin surfaces with divots
– Longer, vertical air bubbles
– Taller, pointier muffin tops
– Chewier, more bread-like texture
Conclusions: Tunnels, a symptom of overmixing, appeared before we tasted any differences in texture. Tough, overmixed muffins were received well by tasters, but they still preferred the tenderness of perfectly mixed muffins.

Testing Method

Ingredients and Equipment

  • 2 c Baker’s Corner bleached all-purpose flour
  • 1 Tbsp Baker’s Corner double-acting baking powder
  • 1/2 tsp Stonemill iodized salt
  • 3/4 c Baker’s Corner granulated sugar
  • 1 c Friendly Farms 1% low-fat milk
  • 1 Goldhen large egg, beaten
  • 1/4 c Carlini vegetable oil, plus extra for greasing
  • 12 2.5-in x 1-in (6.35-cm x 2.54-cm) tins
  • KitchenAid 5-speed mixer

Baking the Muffins

  1. Grease tins and preheat oven to 400°F
  2. Whisk dry ingredients in a large bowl
  3. Whisk wet ingredients in a second bowl
  4. Create a well in the dry ingredients and add the wet ingredients. Stir with a spoon until no dry streaks remain. Batter will be lumpy. Fill two tins with 1/8 cup batter each
  5. Mix remaining batter on Speed 3 for one minute. Fill two tins with 1/8 cup batter each
  6. Repeat Step 5 three times
  7. Mix remaining batter on Speed 5 for one minute. Fill two tins with 1/8 cup batter each
  8. Bake all muffins for 15 minutes or until a toothpick inserted in the center comes out clean
  9. Place tins on a wire rack to cool until they can be handled
  10. Remove muffins from tins and cool completely on a wire rack

Results

To better understand some of these results, I suggest reading the previous posts about gluten, especially the introduction and the section on mixing in this post.

Smoother, runnier batter

As we mixed the batter more, the lumps of dry ingredients combined more evenly into the wet ingredients, resulting in a smoother, runnier batter. Just one minute with the mixer removed the lumps completely.

Tops of overmixed muffins, two per group. As mixing time increased, the muffin tops became smoother.

Smoother muffin surfaces with divots

Given that the batter became smoother, it was not surprising to see the surfaces of the muffins (shown above) become smoother as well. However, the smooth surfaces were punctuated with small divots that formed as a result of the big holes inside the muffins (shown below). When the tunnels form during baking, the muffin batter above the tunnel loses structural support that came from the batter below. If the batter on top of the tunnel has not yet set, it sinks down under its own weight, forming a divot on the top of the muffin.

Insides of overmixed muffins. As mixing time increased, tunneling increased and the muffins became taller.

Longer, vertical air bubbles

As you can see above, as we mixed the muffins more, we saw long, wormy air bubbles, a phenomenon called tunneling. We can discuss this result with an understanding of gluten development. For the sake of this discussion, we can think about gluten like a rubber balloon being filled with air. The perfectly mixed muffin minimizes gluten development, and its gluten network is like an old, brittle balloon that can’t hold much air. As soon as its limit is reached, the balloon breaks and releases the air. However, as the muffin batter is mixed more, a stronger gluten network develops. This gluten resembles a balloon that stretches thinner and thinner as it struggles to hold the air, until “pop!” It finally reaches its limit and the air bursts through the rubber.

The batter of all the muffins contains air bubbles of several gases, which expand and move upward in the heat of the oven to raise the muffin. In the perfectly mixed muffin, the gluten has less strength to contain the air, so the gases gently rise until they reach the surface and evaporate out of the muffin. In the overmixed muffins, however, the stronger gluten holds on to the air. As the muffins bake, the gases continue to expand and exert pressure on the gluten, until “pop!” They finally explode through the gluten with so much force they carve a tunnel in their wake.

As you can see, the one-minute muffin already has a couple unsightly tunnels. Over the course of several muffin tests, we found that even twenty extra strokes by hand resulted in small tunnels.

Taller, pointier muffin tops

To understand the differences in our muffin tops, we need to understand how they form. When the muffin batter hits the heat of the oven, the air bubbles in the batter expand and cause the muffin to rise. This process competes with the cooking and setting of the top of the muffin: the muffin can only rise if the batter is still wet enough to expand in size. If the outside of the muffin has cooked and set, then the size and shape of the muffin can no longer change. Domes on muffins (and all baked goods) form because the outside edges of the batter, which are in more direct contact with the hot oven air, set faster than the insides. While the outsides of the muffin have set and can no longer rise, the insides remain wet and continue to expand. (This also explains why some air tunnels slant toward the center of the muffin: when the air exploded out of the gluten, the batter directly above the bubble had set, so the air had to move toward the middle of the muffin to continue moving upwards.)

As we discussed with the tunneling, the more we mix the muffin batter, the stronger the gluten network is, and the better it can trap air bubbles. Thus, in the overmixed muffins, the batter holds more air in the muffin as it expands. As the outsides of the muffin cook, the additional air in the middle of the muffin contributes to greater rise before the muffin sets, resulting in taller muffins with steep, peaky tops.

Chewier, more bread-like texture

As we described with creatures in tide pools (it makes more sense if you read it!), gluten starts to form when proteins frozen in dry flour become flexible and mobile with the addition of water. When the proteins get close enough to each other, they form the chemical bonds of gluten. As we mix the batter and bring more proteins together, more chemical bonds form and thicken the network of gluten. We can taste this difference in gluten development as a difference in textures. Think about biting through a single cooked spaghetti strand versus a bundle of cooked spaghetti. The single strand, like the less developed gluten in a cake, breaks easily, while the bundle of spaghetti, like the extensively developed network in a baguette, is harder to bite through.

We tasted this difference in our muffins as well. I didn’t taste a difference between the perfectly mixed muffin and the one-minute one, but I could detect the difference by the two-minute one. Interestingly, though, when I shared an early batch of five-minute muffins with my coworkers, they happily ate them and told me how good they were, even after I told them about the experiment. To them, moistness was more important than tenderness for a good muffin. When I presented overmixed muffins with perfectly mixed muffins, however, tasters had a strong preference for the control muffins, describing them as the “softest.”

Conclusions

The more we mix muffins, the more homogenized we make the batter and the more we develop the gluten network. This results in smooth muffin surfaces, tunneling, tall and pointy muffin tops, and a chewy texture. These changes are detectable by eye and by mouth, but if you’re baking for your loved ones, there may be some leeway for overmixing, especially if your muffin is moist and made with love!

References

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

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



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