Wash the beetroot and cook them unpeeled in salted water until soft. In the meantime, mix the yogurt, lemon juice, honey and horseradish. Grate the apples finely into the yogurt mixture.
Peel the beets with disposable gloves and grate them into the apple and yoghurt mixture. Mix well, season with salt and pepper and let cool and steep in the refrigerator for at least 2 hours.