Why are my cupcakes rising funny?

My Mother & I bake hundreds of cupcakes for our business a month from the same recipe, but the last few weeks half the cupcakes have been rising funny, keeping a flat top but splitting and bursting a bit at the side. (See picture) They were all on the back of the pan, but in our fan oven nothing else is coming out different. The baking powder is in date, and we mix them in a Kenwood maker so we're pretty sure it is well mixed. Any suggestions? It is not the end of the world as they get frosted after, but it is still really annoying!

Rachel Phipps
Question image


ChefJune March 21, 2014
The fan may not be rotating evenly. I would have it checked.
ChefJune March 21, 2014
The fan may not be rotating evenly. I would have it checked.
HalfPint March 21, 2014
@Rachel, you might have a hot spot in the back of the oven. You mentioned that half of the cupcakes have this splitting, all in the back. Possibly it is an area that the fan cannot reach as effectively. Possibly the fan is not functioning at full speed. Uneven cooking is one of the prime reasons cakes crack or split. Tops and sides are cooking at different rates. Might be best to have the oven checked out, especially the fan.
Rachel P. March 21, 2014
No real weather changes, or batch changes. And as for the oven, we don't have a thermometer in there, but nothing else have we had issues with. Two experienced cooks using the same oven we've used for years practically every day, we notice when the oven is out. But thanks so much for your suggestion!
The L. March 20, 2014
Out of curiosity, has the weather changed significantly during this stretch? More or less humid than previously? Or perhaps the # of cupcakes being made at a time? Finally, I assume your oven is calibrated. Does an oven thermometer concur with what the dialed temperature says?
Maedl March 15, 2014
Try a library--the book is available in the UK. Your photo doesn't give much perspective so it is hard to tell what's wrong with it. You might want to look at http://www.finecooking.com/articles/how-to-mix-and-make-best-muffins-cakes.aspx
Maedl March 15, 2014
I believe Joy of Cooking has a section with diagrams of cupcakes that have a variety of problems--like over-mixing, baking too fast or slow, etc. Take a look at it and see if anything looks similar.
Maedl March 15, 2014
PS It may be muffins, but I bet the problems would be similar.
Rachel P. March 15, 2014
British so therefore I don't have a copy of Joy Of Cooking?
Recommended by Food52