Language / Help with Polish language - I'm confused by the noun change when a negation is added - genitive case [5]

Hello (and I apologize if this has been covered, I'm new here). I'm learning Polish through Babbel for an upcoming trip to Poland. And I'm confused by the noun change when a negation is added. For example: I like beer: Lubie piwo - But I don't like beer: Nie lubie piwa. Why does "piwo" change to "piwa" with negation. I've noticed the same with wine. Your help is greatly appreciated.