Oil in Muffins

Fats get a bad rap for being unhealthy, but they determine texture in our bakes. They’re also an integral part of our diets. Nevertheless, we often minimize the fat in recipes for health reasons. But how low can we go? In this post, we’re reducing the fat in muffins and exploring the subsequent effects on shape, texture, and shelf life.

Experiment Overview

Goal: To taste differences in muffins made with different amounts of oil
Recipe: Best Ever Muffins from AllRecipes
Method: Mix and divide the wet ingredients except for the oil. Add half, two-thirds, equal, or twice the oil in the recipe to each portion. Add the wet ingredients to the dry ingredients. Bake, cool, and taste.
Results: As the amount of oil in the muffins increased, we noticed
– Sharper peaks
– More tender texture
– More moistness
– Better crumb
– Slower staling
Conclusions: Though fat is not necessary to create a muffin shape, it’s crucial for a muffin texture. There’s no way around it. Oil is low in saturated fats, which makes it a healthier choice than solid fats like butter, but we need it in our batter to make a moist, tender muffin.

Testing Method

Ingredients and Equipment

  • 250g (2 c) Baker’s Corner bleached all-purpose flour
  • 1 Tbsp Baker’s Corner double-acting baking powder
  • 1/2 tsp Stonemill iodized salt
  • 150g (3/4 c) Baker’s Corner sugar
  • 167g (2/3 c) Friendly Farms Vitamin D whole milk
  • 73g (1/3 c) water
  • 1 Goldhen large egg
  • 1/4 c +1/2 tsp Carlini vegetable oil, divided
  • Whisk
  • Rubber spatula
  • 12-cup muffin pan lined with cupcake liners

Baking the muffins

  1. Preheat oven to 400°F.
  2. Whisk the flour, baking powder, salt, and sugar together in a large bowl (414g total). Divide into four portions (103g each).
  3. In a separate bowl, whisk the milk, water, and egg together (288g total). Divide into four (72g each). To each portion, add 1-1/2 tsp, 2 tsp, 1 Tbsp, or 2 Tbsp oil and whisk well to combine. These contain half (1/2), two-thirds (2/3), equal (1x), and double (2x) the amount of oil written in the recipe, respectively. Add each portion of the wet ingredients into a portion of the dry ingredients, and fold until just combined.
  4. Divide each portion of batter into three muffin cups. Muffins from each group weigh 58g, 58g, 59g, and 62g, respectively.
  5. Bake for 20 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 reviewing the post on how fats add tenderness to baked goods. It may also be helpful to review the roles of gluten in structure and texture.

Sharper peaks

As you can see below, as the amount of oil in the muffins increased, the muffin tops became sharper. Whereas the half-oil muffins were more domed, the twice-oil muffins were peaky. These differences reflect how quickly the muffins cooked.

The more oil in the muffins, the pointier their muffin tops.

As a muffin bakes, gases trapped in the batter expand and raise the muffin until the top crust sets. A peaky muffin forms when the center of the muffin cooks more slowly than the edges. Even though the edges cook and set, the center continues to rise, and the muffin develops a sharp peak. A flat muffin top forms when the center cooks at about the same rate as the edges. The top crust sets across the entire muffin, and the center can’t rise up any further.

In the photo below taken about 14 minutes into baking, the half-oil muffins have almost reached their final shape, but the twice-oil muffins still have more rising to do in the center. So the more oil these muffins contained, the more slowly they cooked, and the sharper their peaks.

14 minutes in, the muffins with less oil were cooked more than the muffins with more oil.

To understand how oil affects the speed of baking, let’s first discuss what it means for a muffin to bake. Muffin batter cooks when proteins and starch from egg and flour get hot enough to set into a scaffolding that holds its shape. That’s how the liquid batter becomes a solid muffin. The exact temperature where this happens depends on several factors, including the amount of water available to the proteins and starch. The less water, the hotter they need to be to solidify, the longer they take to set. The muffins with more oil cooked more slowly in this experiment because their proteins and starch had a harder time accessing water.

Because water and fat don’t mix, oil actually blocks proteins and starch from finding water. Just as a layer of fatty mayo or cheese prevents sandwich bread from getting soggy, a layer of oil between the structural molecules and water prevents the molecules from hydrating. Ultimately, this delays them from setting, they cook more slowly, and the muffins form a sharper peak.

More tender texture

Oil also slows cook rate by reducing the density of gluten structural molecules in the muffin batter. We can see the effect of this in the texture of the baked muffins. The half-oil muffins were tough and chewy, while the twice-oil ones were crumbly and almost mealy. These differences were obvious to both taste testers and me, and we strongly preferred the textures of the equal-oil and twice-oil muffins.

The structure and texture of the muffins largely comes from the flour protein gluten. If we think about an egg white, which contains a lot of protein, we know that it becomes rubbery the longer we cook it because the proteins clump together. Similarly, bakes that contain dense networks of gluten, like bread, are tough and chewy, while those with sparse gluten, like cake, are tender.

Fats like oil actually prevent gluten from forming in the batter when they create a barrier between the protein and water. Without water, the individual proteins that make gluten can’t even link up together. So in the muffin batters with more oil, the gluten is sparsely distributed. As a result, they bake more slowly, and their texture is tender. In the half-oil muffins, gluten clumps together to form a dense scaffolding that helps the muffin set faster. These globs of protein also make the muffin chewy.

Fat coats the proteins that make gluten and prevents them from linking together.

More moistness

As the amount of oil in the muffins increased, the moistness of the muffins increased as well. The low-oil muffins weren’t unpleasant, but the tasters and I liked the equal-oil and twice-oil ones much more. You can see the moistness in how easily the paper liners peeled off the muffins. The twice-oil ones came off beautifully.

The more oil in the muffins, the more easily the liners peeled off.

Oil increases moistness in a couple ways. Because oil prevents proteins from absorbing water, there’s more free water in the batter and the baked muffin. Furthermore, we perceive the liquid oil as moistness when we eat the muffin. The more oil, the more moistness we taste.

Better crumb

As you can see, the equal-oil muffins have a fairly regular crumb, but the low- and double-oil muffins are riddled with long, vertical holes. These are called tunnels, and we also saw them in overmixed muffins and low-sugar muffins. As we discussed in detail with the overmixed muffins, tunnels in muffins can be symptomatic of excess gluten development.

Reduced-oil muffins contained more tunnels.

In this experiment, the low-oil muffins developed too much gluten because there wasn’t enough oil to prevent the proteins from linking together. As the muffins baked, the air expanded and the gluten stretched like a balloon until it set. Because the gluten was too strong, it held onto the air, and the pressure climbed as the temperature increased, until Boom!, the air shot out through the gluten balloon with so much force it carved a tunnel.

In the double-oil muffins, the tunnels formed because the batter was too wet. The excess oil thinned the batter, so the air bubbles rose too quickly, leaving tunnels in their wake.

Slower staling

I baked and tasted these muffins with the first taste tester in the morning. They sat on the counter uncovered until I came back with the second taste tester that evening. By that point, both the half-oil and two-thirds oil muffins started tasting stale, but the equal- and twice-oil muffins were still fresh.

One of the reasons baked goods stale is because starch molecules reorganize into hard crystals over time. Oil prevents this in two ways. First, by limiting the amount of water available to starch and requiring that the starch reach higher temperatures to cook, it reduces the number of molecules in the muffin that will recrystallize and harden. Second, the oil sticks to starch molecules in the baked muffin and prevents them from recrystallizing. Ultimately, oil slows the staling process and increases the shelf life of the muffins.

Conclusions

Oil is crucial for texture in bakes. Even a one-third reduction in oil for these muffins created a tougher, chewier muffin that staled faster. Although the acceptability of the reduced-oil muffins is up to an individual’s tastes and preferences, reducing fat changes a recipe at the molecular level and produces a different bake. For more healthful baking, one alternative is to use liquid vegetable oils, which contain less saturated fats, trans fats, and cholesterol. As we saw in the last experiment, they can create more tender and moist bakes than butter!



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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