In a weeks time I will be purchasing 300lbs of Merlot grapes from a vineyard. The owner of the vineyard is going to crush and de-stem the grapes for me. I plan on using a cultured yeast for fermentation. Is it absolutely necessary to use campden tablets, and is potassium/sodium metabisulphite the same thing. How much do I need to add to my 300lbs of grapes.