(It is very important that no egg yolk gets into the egg white and that all materials are clean and grease-free)
Preheat the oven to 90 degrees (fan). Cut the lemon in half and rub the bowl and the beaters of the mixer with the lemon. If necessary, remove the leftover lemon with a paper towel.
Beat the egg whites with a mixer until foamy. Add the sugar little by little and mix well. Mix well for another 7 to 8 minutes until the foam is firm and glossy. Slowly fold the Spirulina into the mixture. If nice peaks form, the meringue foam is good.
Use a piping bag to make nice dollops of egg white on the baking paper. You can also scoop small heaps on the baking paper with a spoon, so you get more round and convex meringues. The heaps do not expand during baking so you can put them quite close together. Place the baking tray in the oven for 1½ hours.
Then open the door of the oven ajar and let the meringues cool in the oven. This allows the moisture to escape and the meringues dry better. Store the meringues in a dry place. Or put them in a drum with some uncooked dry rice on the bottom, so they stay longer crispy.