Probably the least used of the three types of meringue, Swiss is actually the most stable. The protein structure of the egg white traps the air bubbles when it is whisked and the sugar serves to stabilise this (making it taste delicious in the process). Although it is possible to make Swiss meringue without a thermometer it is better to be precise. Swiss meringue can be stored in the fridge for up to 24 hours without weeping (when a pool of liquid begins to appear), a common issue with Italian meringue.