Sodium Nitrate is a bacterial inhibitor, to prevent spoilage organisms from getting a foothold-especially the Clostridium sp. My guess is this Gouda has a very high moisture content even for this cheese type and needs some extra protection from the NaNO3. Some raw milk cheese makers have used NaNO3 to prevent early and late blowing of cheese. Gouda, Edam and other washed curd type cheeses are prone to contamination via the wash water, Listeria is a major worry in large scale low temp wash curd production.