When whisking egg whites and sugar to make meringue mixtures it is best to whisk on medium or medium-high speed, NOT high. It will take a couple of minutes extra for you to create your meringue but the final mixture will be made up of tiny, even air bubbles – which is exactly what you are after! It will be smooth, thick, and glossy and have a shaving cream-like consistency which will give you a crisp meringue that won’t crack when baked. Meanwhile, a meringue whisked on high speed will end up with large, uneven air bubbles and a frothy consistency which will often rise and crack when baked. So, remember to whisk on medium, or if you are a little impatient, no higher than medium-high when making meringue.

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.