Learn the science behind:
Want a smooth, slightly crackly, top on your brownie, but have no clue on how to get there?
There are ample hypotheses floating around online. Some say you need to mix sugar with melted butter, others say to add more chocolate, yet others swear by refrigerating the batter to guarantee a beautiful crackly topping. But which one is true? Or do they all work? In our quest, we found that whisking eggs before adding them to the batter worked best. But why?
- What is a crackly top?
- Lesson 1: Whipped eggs are key for a crunchy crust
- Lesson 2: Creaming sugar & butter is the secret
- Ingredients & Steps that did not work
- What's your trick?
What is a crackly top?
There are tons of brownie recipes out there and each brownie will look and taste a little different. Previously, we discussed how to tweak your brownie to either become gooey or cakey in texture. Here, we’ll be focusing on that top layer. When we’re trying to make a smooth, crackly top we’re aiming for the type of brownie marked C in the photo below. It looks pretty smooth and shiny and has a few cracks. What’s more, the top is slightly crunchy, which is a nice contrast to the softer brownie interior.
That said, brownies A and B might not look the most beautiful, but they did have a very crunchy crust. If that’s what you’re looking for, those would be good options also. A wide range of theories floats around the internet on how to create either that smooth crackly top (C), and a crunchy crust (A and B). To verify some of those, we baked a bunch of brownies and evaluated the results.
Lesson 1: Whipped eggs are key for a crunchy crust
In brownie recipes that use eggs we found that whisking the eggs before mixing them with dry ingredients was key to creating a crunchy texture. We found that this goes both for whisking the eggs separately, as well as whisking them with some whipped butter and sugar.
The 4 brownies in the image above were all made with the same recipe (the one given at the bottom of this article). The only difference was in how we mixed the ingredients together:
- Brownie D, the one without a crunchy or crackly crust was made by melting the chocolate and butter and then simply folding in all the other ingredients.
- Brownies A-C all involved a step in which the eggs where either whisked light and airy separately, or mixed fluffy with other ingredients.
Baking was done in an identical manner since they were all baked in the same tin, for the same amount of time.
The only brownie that did not have a crust that could be easily distinguished from the rest of the brownie was brownie D. It had a more or lesss even consistency throughout, whereas the others all had a crunchy crust around a soft inside.
Why it works: Eggy foams rise up
A brownie batter is quite a delicate batter. Compared to cakes for instance, it contains a low amount of flour, which helps to stabilize the batter. As a result, when the batter enters the oven it becomes quite liquid at first – both the butter and chocolate melt completely – before the eggs and flour have time to stabilize the mix. As a result, physics can do its thing! Light air bubbles have a chance to rise up through the liquid batter and gather on top. Since it’s hot at the top, they won’t necessarily disappear but will hang out there. This creates a foamy top layer that gets very crunchy.
Wondering what those light air bubbles are made of? Exactly, the air bubbles formed by whisking up those eggs while making the brownie. Without them, the overall mix will remain more homogeneous.
Lesson 2: Creaming sugar & butter is the secret
Whisking eggs is a great help for creating a crusty, but we found that by itself it isn’t enough to create that beautiful smoother top of brownie C. To achieve that, there’s an extra step you need to take: creaming butter & sugar. We consistently found that by first creaming butter & sugar and then beating in the eggs, we could get that beautiful smooth crackly top we were looking for!
Why it works: not entirely sure!
Creaming butter and sugar is a common step to take when making a wide variety of cakes. It’s a way to incorporate air into a batter. The butter is whipped up slightly, as a result it becomes lighter in color and has a lot of tiny air bubbles spread throughout. By adding the sugar, you help some of that sugar to dissolve in the butter’s water. That said, there’s not enough water in the butter to dissolve all the sugar, so there will still be sugar crystals left.
We’re not completely sure why this step, combined with whisking in eggs, makes such a difference. Again, it most likely has to do with density differences in the batter, allowing a light airy part of the batter to rise to the top. Somehow, that gets a chance to spread out very smoothly, to form that characteristic top. We won’t say it works for every single recipe out there, but it’s been consistently working in a wide variety of recipes for us.
Ingredients & Steps that did not work
There were also several hypotheses that we tested that did not have a noticeable effect on the appearance of the brownie and the formation of a crust. We’ll list them here quickly. Who knows, they might work in some cases, but we didn’t get consistent results with them at all
More cakey recipes gave a less beautiful top
Even though whisking eggs generally improved the crustiness of a brownie’s top, it didn’t work in all cases. We found that brownies that were considerably more cakey, got less of this special top. Since these brownies contain less fat and more flour, generally speaking, this probably makes it a little harder for that phase separation to take place. As a result, recipes with relatively more flour and cocoa powder and less chocolate and butter gave less consistent results.
Mixing sugar into molten butter & chocolate does not work
Some recipes claim that the crackly top of a brownie is made by mixing the sugar in hot, molten butter and chocolate. We did not find that this has a consistent impact. As an explanation for why it works, some may say that the sugar dissolves in the warm butter. However, in our experience, there is not enough water in the butter to dissolve all the sugar. And, sugar doesn’t dissolve in fat. When doing this, we generally still felt plenty of sugar crystals and it just didn’t give the top we were looking for.
We did notice that recipes that call for melting both the butter and chocolate are more prone to separating in the oven. That is, more prone to forming a puddle of fat at the bottom of the brownie. It doesn’t happen for all recipes, but working with too much liquid fat in a batter when it goes into the oven does seem a risk factor for this to happen.
Refrigerating the batter does not help
Refrigerate the brownie batter overnight and your crackly top will improve. At least, that’s what they said. But, we didn’t see any major impact. If indeed the phase separation of the foamy eggs/butter mixture from the rest of the brownie is key, this could theoretically work. However, since chocolate sets in the fridge, it’s not likely for this to happen in the fridge. The batter solidifies too much. Again, it might work for some, but when testing recipes, we found that simply whisking and creaming the ingredients gave better more consistent results.
Using icing sugar did not make a difference
Some claim that using icing sugar instead of granulated sugar helps to create a crackly crust. Again, we did not find an effect here. Testing a recipe with both sugars did not significantly impact the result.
Mixing in add-ons can ruin the top
A recipe that makes a beautiful crackly top can be ruined by mixing in too much add-ins. For instance, we decided to mix in some caramel sauce to one of our brownies. Whereas the brownies still turned out perfectly delicious, the topping clearly looked different. It wasn’t horrible, but it hard clearly interfered with whatever is exactly going on when the smooth crackly top is formed.
What’s your trick?
So, which ingredients and which method do you use to create those crackly topped brownies? Or, do you maybe prefer brownies with a different top, more fudgy, gooey, and shiny? Let us know!
Tessa Arias, How to Make Brownies with Shiny Thin Crust, Handle The Heat, May-3rd, 2021, link
Emma Christensen, Perfectly Sweet: How to Get a Crunchy Top on Brownies, Kitchn, Oct-26, 2009, link
Cakewhiz, How to Make Fudgy Brownies With Crackly tops, Nov-5, 2015, link