Macarons can have sticky bottom shells due to a number of issues. Macarons will turn out under baked, but there are a few changes you can make to prevent your next batch of macarons from having sticky bottom shells.
Using stainless steel baking pans vs aluminum for macarons
Stainless steel baking pans can get hot spots over time. The uneven distribution of heat in older stainless steel pans can make macarons have sticky bottom shells, and will come out of the oven undercooked.
Aluminum is the best metal for conducting heat over other baking sheets like stainless steel.
Aluminum baking pans conduct heat evenly throughout the pan.
Aluminum is a light colored baking sheet; it doesn’t absorb heat like other metals, such as stainless steel.
With a lighter colored pan, you can bake your macarons for a shorter amount of time than if you used a stainless steel baking sheet.
Using an oily baking pan for macarons
Macarons need to be baked on a baking sheet that is perfectly clean.
There can be no oily residue present on the baking sheet. If there is any presence of oil on the baking pan, the macarons will absorb the oil and will not turn out. The macarons will be sticky, under baked, or will not turn out at all.
If you’re having trouble removing the oily residue from your aluminum baking pan, pour very hot water on the pan, and this should remove the oil from the baking pan.
Using an oily silicone baking mat for macarons
If you’re using a silicone baking mat to line your baking sheet, make sure there is no oily residue left on the baking mat before piping your macarons.
Your macarons will absorb the oil, and will have sticky bottoms.
If you’re not able to get your silicone baking mat clean, try using a fresh sheet of parchment paper to line your baking sheet. Another option is having a separate silicone baking mat to only use for macarons.
Cut the parchment paper to fit to the pan. It’s much easier to pipe close to the edges of the baking pan if the parchment paper isn’t overhanging the edges.
Macarons are under baked
Use an oven thermometer to check the temperature of your oven before baking your macarons. Make adjustments as needed for your recipe.
If your first batch of macarons come out of the oven with sticky bottoms, try baking the macarons for 1-2 minutes more. Keep a close eye on them as they can burn very quickly. You can use a baking utensil to check the bottom of one of them while they are in the oven to check to see if they are done.
Meringue for macarons is mixed too long
If your egg whites are mixed too long for your meringue, your macarons can be hollow inside and have sticky bottoms. Try whipping your egg whites for less time to prevent this from happening. Your egg whites are finished when you can turn the mixing bowl upside down and the egg whites don’t move. Check periodically on them as you whip the meringue.