Why Does My Cake Have Holes and Tunnels

Slice a cake and find narrow channels running up through the crumb, or a few large, round holes scattered among an otherwise fine texture, and you are looking at two different problems. Tunnels usually come from gluten and steam working together in a batter that was mixed too hard or baked too hot. Isolated round holes are more often air pockets trapped while the batter went into the pan.

This guide shows how to read the shape of the holes, then works through the causes one at a time: mixing, leavening, pan filling and oven temperature. Most fixes are small adjustments to technique rather than changes to the recipe.

Read the shape of the holes

The pattern tells you where to look. Long, wormlike channels that run vertically or at an angle toward the dome form during baking, as gas and steam push through a crumb with too much structure. Round, smooth-walled holes that sit randomly through the cake formed before it went into the oven, from air that was folded in or trapped. Very small holes concentrated in one area, sometimes with a darker or discolored rim, come from leavener that was not evenly distributed.

• Vertical tunnels: overmixing, excess leavener or a hot oven
• Large round pockets: trapped air from scooping or layering batter
• Pinholes with off-color or bitter taste: unsifted baking soda or powder
• A coarse, open crumb throughout: overcreamed butter or too much leavener

Overmixing after the flour goes in

Wheat flour forms gluten when it is wet and agitated. A little gluten helps a cake hold its shape, but beating the batter hard after the flour is added builds elastic strands. As the cake bakes, expanding gas cannot escape evenly through that stretchy network, so it forces its way up in channels.

Add the flour on low speed or fold it in by hand, and stop as soon as no dry streaks remain. Finish with a few strokes of a spatula from the bottom of the bowl to catch any unmixed flour. Recipes that alternate dry and wet ingredients rely on this gentle approach; using the mixer on high for the final additions is a frequent cause of tunnels in pound and butter cakes.

Air trapped while filling the pan

Thick batters such as pound cake, carrot cake and chocolate cakes made with sour cream do not settle by themselves. Dropping spoonfuls into a pan leaves gaps between them, and those gaps bake into round holes.

Spread the batter into the corners with an offset spatula, then tap the filled pan firmly on the counter two or three times to bring large bubbles to the surface. In a Bundt or tube pan, run a thin knife or skewer through the batter in a zigzag before baking. For marble cakes, layer the batters gently and swirl with a few deliberate passes rather than many small ones.

Too much leavener or uneven leavener

Excess baking powder or baking soda produces more gas than the batter can hold. Bubbles merge into larger ones and rise through the crumb, leaving holes, and the cake may also dome sharply and then sink. Measure leaveners with proper measuring spoons and level them off; a heaping teaspoon can be half again what the recipe intends.

Baking soda in particular tends to clump in the box. Lumps that are not broken up leave pockets of concentrated soda, which create small holes and taste soapy. Whisk the leavener thoroughly with the flour, or press it through a fine sieve with the dry ingredients.

An oven that runs hot

When the oven is hotter than the dial says, the outside of the cake sets before the center has finished rising. Gas still expanding in the soft middle has to push up through the firm top, which drives tunnels and often causes a peaked, cracked dome.

Place an oven thermometer in the center of the rack and compare it to the setting after a full preheat. If it reads high, lower the dial to compensate. Baking in a dark metal pan or on a rack too close to the top element has a similar effect, so use the middle rack and a light-colored pan when you can.

Creaming too long or too little

In the creaming method, beating butter and sugar traps tiny air cells that leaveners later enlarge. Underbeaten butter leaves too few cells, and the cake bakes dense with occasional large holes where leavening gas collected. Overbeaten butter, especially if it was too warm, can hold large, unstable bubbles that merge into a coarse crumb.

Start with butter that is cool room temperature, around 18 to 20°C (65 to 68°F), so it bends without being greasy. Beat with the sugar for about 3 to 5 minutes on medium speed until pale and fluffy, then add the eggs one at a time.

Common questions

Are tunnels in a cake safe to eat?

Yes. Holes and tunnels affect texture and appearance, not safety, as long as the cake is fully baked. If the tunnels are paired with a bitter or soapy taste, the cake contains too much or poorly mixed baking soda; it is still edible but may be unpleasant.

Can I hide tunnels in a cake I need to serve?

For a layer cake, a crumb coat and frosting will cover holes on the cut sides. Trimming the domed top often removes the worst of the tunnels, since they tend to run upward. For a loaf or Bundt, slice and serve with fruit or cream, and note the fix for next time.

Why do my muffins get tunnels more than my cakes?

Muffin batter has less fat and sugar to tenderize it, so gluten forms more easily with each stir. The same overmixing that is mild in a rich cake becomes obvious in a muffin. Our muffin tunnel guide covers that case specifically.