Old ginger has a stronger flavour than the young so I use old. My recipe for a good strong tasting ginger beer is:- 1 tin of Cooper's ginger beer, 1 kilo of dextrose, 1 750ml bottle of Bundaberg original natural ginger beer cordial and 2 large old ginger roots. Sanitise the food processor and pulverise the root, place in hop bag, boil about 1.5 litres of water, turn off and steep the ginger for half an hour. Put the liquid and the bag in the fermenter and off you go. I like to make it now for summer (have 90 long necks ready, yum).
hope this is of interest, cheers