Сум is a traditional Russian dish made from fermented milk, often enjoyed as a refreshing beverage. It is typically prepared by allowing milk to sour naturally, resulting in a tangy flavor. Sums can be served chilled and is popular in various regions of Russia, especially during the summer months. The preparation of сум involves a simple fermentation process, where beneficial bacteria convert lactose into lactic acid. This not only enhances the taste but also increases the nutritional value, making it a source of probiotics. Sums can be enjoyed on their own or used as an ingredient in other dishes, such as soups or sauces.