In two different courses, I have flashcards for ‘beer’ and ‘draft beer’. The hiragana given for ‘beer’ is びーる while the hiragana for ‘draft beer’ is なまびいる.
Are these interchangable methods(い vs ー) of showing the double ‘i’ or is there some distinction I’m missing?
おねがいします
In my experience, “beer” in Japanese would usually be written with katakana, ビール.
Foreign words written in katakana usually use the length mark for long vowels, while native Japanese words (in hiragana) usually use ああ ええ いい おう (sometimes おお) うう.
So it seems that when transcribing the katakana into hiragana, one of them kept the length mark, while the other “japanised” the spelling while putting it into hiragana.
In the end, both of the spellings are unnatural as you will usually see it written in katakana, not hiragana, in Japan itself 
ありがとう!
I really appreciate the answer. One of the most frustrating things for me so far is how difficult it is can be to search for the answer to a question, since I get pages of Japanese results when I try. 