Ok I am at witt end. I have over 100 batches of all grain under my belt. THe last 5 batches I have brewed have a sour taste to them. I have cleaned everything several times. I have changed tap lines and even the gas line. I have used a brand new picnic tapper. I have brewed a couple of ales a kolsch and a porter the taste is still there. Anyone have any idea where the problem could be?