How do Italian wine classifications like DOCG, DOC, and IGT differ?

Italian wine classes are about the local origin, production methods and the kind of grapes. DOCG (Denominazione di Origine Controllata e Garantita) exceptionally brightens the highest quality of wines which are strictly governed by law. DOC (Denominazione Di Origine Controllata) wines have the additional possibility that they can be more justified but still need to obey certain rules. The IGT category -- that's I'm referring to -- is a much wider governed, with its producers having more flexibility in terms of grapes and winemaking techniques.
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