Does your coffee taste bitter? Sprinkle a few grains of salt to make it taste better. As salt dissolves it releases sodium ions which blocks your taste receptors from detecting bitter notes. If you are using a french press, avoid using boiling water as it increases the production of molecules that taste bitter.
If you picked up a bunch of green bananas and you don't want to wait a few days for them to ripen you can speed up the process using chemistry. Place them in a paper bag with an apple or ripe tomato then close the bag. The apple or tomato give off the chemical compound ethylene, which is a natural fruit ripening chemical. On the flip side if you don't want your bananas ripening too quickly, don't place them in a bowl with other ripe fruit.