Peel and chop the ginger. Wash limes and oranges hot, dab dry and peel the peel thinly. Squeeze the limes. Bring 2 l water, sugar and ginger to the boil and simmer for about 1 minute.
Mix the citrus peel and lime juice in a jug. Pour the hot ginger stock over it and let it cool down at room temperature. Then cover and leave to stand in the refrigerator for 1-2 hours (depending on how hot it is).
Pour the ginger beer through a very fine sieve or a moistened gauze cloth. Half fill eight glasses with crushed ice. Spread ginger beer on top. Fill up with mineral water as desired and garnish with mint.