Aged cow cheeses from the European Union are a wide selection of organic milk products. They have characteristic taste and aroma. Cheese ageing is a long and complex biochemical process that uses diversified microbial flora. The gases released during ageing (specifically carbon dioxide) leave characteristic holes in cheese. Cheese may be soft or hard, depending on how long it is aged – from a few days to a dozen or so months. Aged cheese is highly valued and used in many different cooking styles. It may be served as starter, in sandwiches and salads as well as in sauces, e.g. pasta sauces.