Set the oven temperature to 100°C (210°F) fan-forced, and line two large baking trays with parchment paper.
Start by separating the egg whites from the egg yolks. Make sure there are no traces of egg yolk in the egg whites.
Add the whites to a bowl of a stand mixer fitted with a whisk attachment. Beat at a low speed until little bubbles form.
Increase the mixer speed to medium-high and whisk until the egg whites are white and frothy. Add the vinegar while the mixer is running.
With the mixer running at high speed, add the caster sugar one tablespoon at a time. Waiting about 45 sec between each addition.
Once all of the sugar has been added, continue whipping the meringue for a further 10 minutes at high speed. At this stage, your meringue should have more than doubled in size, and stiff peaks should have formed. If you'd like to color the meringue mixture, you can do this now.
Place the meringue mixture into a piping bag fitted with your chosen piping nozzle. Pipe the mini meringues onto your prepared trays.
Bake the meringues in a preheated oven for about 20 minutes or until the bottom of the mini meringues lifts easily off the parchment paper.
Switch off the oven and allow the meringues to dry out in the oven for about 2 hours or overnight. Store in an airtight container until needed.
Notes
Make sure there are no traces of egg yolks in the egg whites, and no traces of fat on the whisk or in the mixing bowl.
Do not let the whipped meringues sit for too long before piping them. Otherwise, the texture will change, and you risk losing all your hard work.