Sour or severe.

an acrid or sour flavor. A fault in coffee sometimes due to over heating. Like when you leave the glass coffee pot on the heater and tste it a few hours later.

A taste fault in the coffee brew giving an acrid and sour sensation on the tongue. The result of excessive heat after brewing which stews the coffee.

sour or bitter in taste

harsh or corrosive in tone; "an acerbic tone piercing otherwise flowery prose"; "a barrage of acid comments"; "her acrid remarks make her many enemies"; "bitter words"; "blistering criticism"; "caustic jokes about political assassination, talk-show hosts and medical ethics"; "a sulfurous denunciation"

A term referring to a taste fault in the coffee brew that leaves an acrid and sour sensation on the tongue.

is anything sour, bitter or sharp - cutting, caustic, acid, mordant, barbed, prickly, biting, pointed. The opposite flavor would be mild, sweet, or honeyed.