How was 辣 used before the Columbian Exchange?
in ancient time, "辛" was used, in lieu of 辣. e.g. in 洪範:

潤下作鹹﹒炎上作苦﹒曲直作酸﹒從革作辛﹒稼穡作甘

http://ctext.org/shang-shu/great-plan/zh?searchu=潤下作鹹，炎上作苦，曲直作酸，從革作辛，稼穡作甘%E3%80%82&amp;searchmode=showall#result

nowadays, dictionary would explain 五味 as 甜﹒酸﹒苦﹒辣﹒鹹, instead of older terms 甘﹒酸﹒苦﹒辛﹒鹹

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000159662

i guess the taste 辛 was gotten from 薑 ( ginger ), 花椒 ( Zanthoxylum ); that these two were native chinese plants.

last, the character "辣" is derived from "辛" &amp; "剌"

http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/search.php?word=辣

well, more info:

the book 酉陽雜俎 of 唐 dynasty (618-907) mentioned "胡椒" (pepper) and associated its taste to the terms "辛辣"

酉陽雜俎　卷十八, ~p112 of the pdf file:



胡椒 - pepper

摩伽陁國 - magadha, a kingdom in ancient india

another casual found:

the term "辣椒" (chili pepper) is first used in 漢文大藏經　百癡禪師語錄　卷三 (around 1644-1661):

張空火傘熱難當
何處幽陰可隱藏
莫道太平無款待
濃煎幾碗辣椒湯


http://tripitaka.cbeta.org/J28nB202_003, [0016b07]