Cracked Meringues

1. The first and most common reason (and what happened to the meringues in the front of this pic) is that the oven temperature is too high. The intense heat will cause the air bubbles in the mixture to expand efficiently, causing it to rise, spread and crack. The meringues behind them were from a second batch that were baked in an oven preheated to 10°C lower (yep, sometimes that’s all it takes!) and resulted in perfect, smooth-crusted meringues without cracks.
2. The second reason is that the mixture has been whisked on high speed with an electric mixer. The furious and quick incorporation of air into the egg whites will form an airy foam with lots of large air bubbles. When baked these large masses of air have a greater ability to expand than smaller air bubbles, causing the mixture to rise, spread and crack unevenly. If this is the case, the best solution is to whisk the egg whites and sugar mixture on medium or medium-high speed which will form a denser foam made up of lots of tiny, even bubbles that, when heated, will only expand slightly, if at all, minimizing any rising, spreading and cracking.