Can't image what the gunk might be. I add more StaFlo starch to mine vodka mixture as I want lots of stiffness to my fabrics. Because of that I keep my mixture in the fridge as the starch will go moldy on you if it gets a bit warm. Found that out the hard way. Anyway, now I make up a gallon at a time as I normally will starch a bunch of fabrics at one time, hang them up to dry and then press them at one time.