Cut the plums into small pieces. Peel the bananas and cut them into slices. Cut the apple into cubes (you don’t need to peel the apple, just remove the core with the seeds).
Place all fruits in a blender bowl. Pour in kefir (or unsweetened yogurt). For a sweeter drink, add some honey. Grind everything until smooth. Fruit smoothie with kefir is ready.
Serve the plum, banana, and apple smoothie right away, otherwise, after 5 minutes it will start to darken and lose its beneficial properties.