why does my weed smell like fresh cut grass?

Here is an inexpensive drying rack i made. scrap particle board a couple eyelets and some wire. hold about 3 plants worth. cost minimal. go to a cabinet shop and ask for some scrap wood.i have it in a dark spare bedroom with a ceiling fan circulateing air. i dry 5 to 7 days till stems bend like they wanna break, but not snap. then i open jars 2 hours every 12 till cured right. how do i know when done........... thats your best tell....