Buy your fresh ginger and cut into useable size chunks. No need to peel! Pop in a freezer bag then into a freezer box and freeze. Grate what you need immediately and pop any left over back to the freezer. Don’t let it sit as it goes soggy and not so easy to grate. I do exactly the same with peeled cloves of garlic. Always grate immediately after taking from the freezer. No waste ever and always at hand.