I remember reading about bar competition on making best cocktail from Birch sap . It is a popular beverage. This is probably the best known Belarusian brand of birch sap abroad.
Homepage of the producer : http://www.byarozavik.com/en/
Byarozavik is a natural birch tree juice harvested using tried-and-true traditions and has been preserved according to its original recipe just for you!