The acidity is the measure that determines the acid content in the oil. The more acids the oil contains the more "neutral" and "flatter" is the taste and even more difficult to digest. The highest quality oil, i.e. "extra virgin", has acid content of less than 0.80%. Oils that only meet the criterion of acidity are not classified as extra virgin because they can derive from mixing oils and chemical processing. This process is not considered as adulteration if the consumer is fully informed.