Preheat oven to 150°C.
Line two large trays with parchment paper.
Using a stand mixer, whisk the egg whites at high speed until stiff peaks form. Gradually add sugar, one tablespoon at a time, leaving about 1 minute between each addition. When the sugar has been incorporated, continue whisking for another 5 minutes or until the mixture is stiff and glossy.
Scrape down the sides of the bowl, add the vinegar, and mix for 2 minutes or until vinegar is thoroughly incorporated.
In a small bowl, combine instant coffee, melted chocolate and vanilla extract.
Scoop the meringue out in rounded spoonfuls onto prepared trays, leaving about 3-5cm between each mound. Spoon a small amount of the coffee and cocoa mixture (pea size) over the top of the meringue. Using a skewer, make decorative swirls.
Reduce oven temperature to 120°C, and place the trays in the oven. Bake meringue swirls for 30 minutes or until they are crisp on the outside when touched.
Turn the oven off, and leave meringue swirls in the closed oven for another 30 minutes.
Remove the meringue swirls from the oven, and continue cooling on a cake rack.
Store the meringue in an air-tight container once completely cooled.