India, Oct. 31 -- Berlin (dpa) - It's a mistake amateurs make only once. Laying the bottle flat means a sweet and sticky leak at best - and possibly an eruption of fizz all over you. Written on bottles of Germany's Federweisser is a clear warning to keep them upright at all times. That's because this sweet and volatile drink is made from actively fermenting grape juice. Like the leaves changing colour, it rings in autumn when it starts to appear on supermarket shelves in Germany, Austria, Hungary and other parts of Central Europe after grape harvests. As fizzy as it is unpredictable, the drink is constantly evolving. Because the drink is still fermenting when you buy it, the screw cap often has a hole in it and is left loosely open to avoid...