The sugar crystalizes when making a sugar syrup.
Solutions: If any sugar crystals land on the sides of the pan, use a wet brush to brush them down into the syrup. Avoid stirring the syrup after the sugar has completely dissolved and begins to boil.
Egg whites won’t whip.
Solutions: Make sure the bowl, beater, and egg whites are entirely free of any oil or fat, including egg yolk. Avoid plastic bowls, which can retain residual oil. Use metal bowls. Glass is slippery and the whites don’t beat as well.
Neoclassic Buttercream will not firm up after adding the butter.
Solution: Make sure the mixture is completely cool to the touch before adding the butter.
Mousseline buttercream will not firm up and begins to separate after mixing the meringue into the butter.
Solutions: Use an instant-read thermometer to ensure that the temperature is between 65° to 70°F/19° to 21°C and adjust as needed. If not using a thermometer, try adjusting the temperature with just a small amount of the buttercream as described in step 8. If all else fails, with your hands, squeeze out the liquid that has separated and pour it into a large measuring cup with a spout. On high speed, beat the remaining buttercream until it becomes smooth. Then gradually beat in the liquid. The resulting buttercream will be less airy but perfectly emulsified and silky smooth.
The buttercream has an off flavor.
Solutions: Butter readily absorbs other odors, so be sure to store butter and buttercream well wrapped. Buttercream frosted cakes, if refrigerated, should be stored in a container or covered with a cake dome or inverted bowl.
The ganache breaks and separates.
Solutions: Avoid stirring the ganache while it is cooling to room temperature. If you used heavy cream with a low percentage of butterfat, try reheating the ganache slightly and stirring in a little more heavy cream. An immersion blender works best for this because it does not to incorporate air.
The caramel is too dark even though the correct temperature guide was followed.
Solutions: Make sure your thermometer is accurate. Use a light colored silicone spatula to determine by eye the color of the caramel. It should be a deep amber. When the mixture approaches the desired finished temperature, be sure that the burner heat is no higher than medium-low, so that the temperature will not keep rising too much after the pan is removed from the heat. Remove the pan from the heat a little before it reaches the desired temperature or color, because the pan’s residual heat will cause the temperature to rise.