why does my weed smell like hay? my first grow and...

Dried too fast and or put into jars too quickly. Ideally you should hang entire plant and be at 60F at 60% humidity. Goal is a long, slow dry, so that when it goes into jars it's basically done. No need to burp if dried properly.

The Relative Humidity of the drying room was too low. Drying takes between 10 days on drying racks to 20 days if branches are hanged. The process must be done at low temperature, around 18° Celsius and 62% Relative Humidity, away from direct light.

the easiest and simplest way to never f up again curing is buying grove bags. hang the plant, after like a week or 2 trim the weed, put in the bags and the bag will do everything for you. no burping, no boveda packs etc. Thats actually the best and easiest way i've ever cured. (Some also dry and cure in those bags but i dunno, never testet that myself) ;;

If the drying space has no ventilation and lacks fresh air circulation you're very likely to develop that hay smell. If the buds are close to each other humidity may stagnate and will cause the hay smell. Over 60% RH humidity will easily cause the hay smell, especially in a warm environment.