Pick over and wash 1 kg of rowan berries picked after the first frost, then cover with cold water and let it stand 24 hours. Drain berries in a colander, then cover with cold water again and let it stand. Repeat this process 2-3 times. Add water to 1 1/2 kg of sugar, make a syrup, then pour hot syrup over rowan berries, and keep on ice for 24 hours. Take berries with a skimmer, bring syrup to boil, and cook for 20 minutes. Return berries to boiling syrup and cook on medium flame 20-25 minutes, until syrup thickens and berries become shiny. Do not overcook berries, or they will become dry and unappealing.