steam, heat, sultry, foment, get musty
蒸 centers on hot, moist vapor: steam rising, sultry heat, or the process of steaming something. The extended senses of fomenting and getting musty both come from the idea of enclosed warmth and moisture.
蒸 combines 艹 (grass/plant) with 烝, which itself shows steam rising from fire (灬). Together they suggest steam rising from heated plant material, a phono-semantic compound where 烝 contributes both sound and meaning.
Grass 艹 on top of a fire 灬 with rising steam in between: picture a pot of herbs steaming over a flame, filling the air with hot, moist vapor.
For ジョウ, imagine a steaming bowl of miso soup that you need to 'jō' (a made-up word for 'stir' in a thick, hot liquid) to keep it from getting musty: jō -> ジョウ.
steam; vapour; vapor
steaming
evaporation
distillation
humid; sultry
water vapour; water vapor; steam
to steam (food, towel, etc.)
chawanmushi; savoury steamed egg custard with chicken, mushrooms, etc. (savory)
to reheat; to steam over
baking foods in a covered pan; foods baked in a covered pan
vacuum deposition
to be steamed (properly, e.g. rice)
hot and humid; muggy; sultry
transpiration
steam bath
steamer; steam cooker
to cook by steam
fumigation; smoking (out)
filled with steam; sweaty
odamaki mushi; egg custard dish on a base of udon noodles