Condensation is caused by a change in temperature going from cold to warm, and is made worse due to the amount of moisture in the air, aka humidity. (Brisbane summer, we're looking at you!) The steam that forms on the mirror after a hot shower? Condensation. That enticing drip of water rolling down an ice cold bottle of drink? Condensation.
Condensation on cakes is also known as "cake sweat" and can be very frustrating if you are unsure how to conquer it. The name "cake sweat" is slightly misleading, as the moisture that forms on the fondant or buttercream is not coming out of the cake, but is moisture that is being absorbed by the icing. If I was to get technical and science-y, I could tell you about how sugar is a humectant, which means it draws moisture to it. This is great in high sugar mud cakes as it's what makes them moist and yummy. It's not so good when you are working with icings on a hot, humid day. Or even a colder, rainy day :-( It's why meringues will go soft if left out in the air. It's why toffee and isomalt go sticky when not kept in an air tight container.
So with all that in mind, unfortunately condensation is something that will always be around. However, with these helpful hints and tips you'll be able to beat condensation time and time again.
The easiest way to avoid condensation is to avoid putting your cake through temperature changes. Fondant does not need refrigerating, and once a cake is covered in fondant, it is protected from drying out. Most buttercreams (apart from ones that contain milk, cream and cream cheese) are fine left out in a cool environment for a day or two. This isn't advisable in summer of course, but if you have a room with air con that you can leave it in, it will be fine. But if it's the height of summer and you need to fridge or freeze your cake, read on!
Frozen cakes:
If your cake is in the freezer and then taken out and put on the bench at room temperature, this is going to cause condensation due to the dramatic change in temperature. To help minimise the condensation from the freezer, it is recommended to place your frozen cake into the fridge for a few hours, then take it out to come to room temperature. Doing this enables the cake to slowly come back to room temperature to avoid condensation forming on the icing.
Before going into the freezer, chill your cake in the fridge and once very firm, wrap it in cling wrap/film. As the icing is hard now, it won't be damaged by wrapping in cling wrap and will protect the cake from moisture while it is in the freezer. If you have decorated your cake in advance and are popping this into the freezer for an extended period of time, it is highly recommended to cover your cake in cling wrap. Once you are ready to remove your cake from the freezer, leave the cling wrap on and place it directly into the fridge. This will help it gently warm up in temperature before taking out of the fridge completely and removing the cling wrap.
Refrigerated cakes:
You are still likely to get condensation when taking a cake out of the fridge unfortunately, especially in the more humid summer months. To help, put the cake into a cardboard cake box before putting in the fridge. When it comes time to remove your cake box from the fridge, leave the cake inside the box until it comes back to room temperature. Any condensation will form on the box instead of the cake.
If your fridge is not big enough for a cake box (I mean, you probably have a load of other party food in there anyway!) take the cake out of the fridge and into the coolest room you can. If you have air con, have that cranked up to minimise the temperature change. If you don't have air con, place the cake in front of a fan, and spin the cake around periodically so every side gets air on it as it reaches room temp. It may be worth investing a dehumidifier if you don't have aircon. These nifty contraptions take the moisture out of the air, which will minimise the moisture on your cake.
If you are wanting to serve your cake outside or in a warmer climate, it is recommended that you follow the above steps along with ensuring you place your cake in a cool, shady spot away from direct sunlight/heat as this will cause condensation but also will melt your cake. If you can, it's always best leave your cake inside in the cool and bring it out just before serving to avoid any extreme temperature change altogether.
And on that note, although it's not exactly condensation related, I think it's a good idea to be reminded about what heat can do to buttercream. Check out this video of a cake left out in the sun :-(
How to Fix Condensation?
Help, my cake already has condensation - what do i do?? Never fear, you can always fix a cake that has condensation! If you cake has just come directly out of the freezer and its started to form little condensation bubbles, this can be removed by grabbing a flat piece of paper towel and gently pressing this against the side of the cake to absorb the condensation bubbles. If your cake is still chilled/frozen this should not leave any marks or patterns on the icing.
You can also just leave the cake alone. As long it's not super humid, and as long as the cake is not touched after coming out of the fridge or freezer, the cake will sweat and then it will evaporate over time, and no one will be any the wiser. If it IS super humid, the condensation may be so much that runs, so in that case, set your cake in front of a fan as in the tip above.
Remember, a little bit of condensation on a cake is not the end of the world, as it's going to come to room temperature eventually. Keep in mind the above points and you'll be worrying less and eating more ;)