Because "juice" is "juice" in Swedish too. "Saft" is another type of beverage. This is saft: http://halalindex.yasminshamsudin.com/wp-content/uploads/2013/01/saft-antocyaner.png
min, mitt and mina all mean "my", but min is used with words that need en, mitt with words that use ett and mina is used with all words that are plural.
sin, sitt and sina all mean either "his own, her own, its own, or their own" sin is used with words that use en, sitt is used with words that use ett and sina is used with all plural words. Scroll down at this page to see the tips and notes: https://www.duolingo.com/skill/sv/Possessives