The old man actually winced when he tasted the punch. He knew that one of the guests, probably on the groom's side, had surreptitiously added of 12oz of rum to the bowl. Looking around the reception, grandpa counted many suspects. He also noticed that most of his friends, senior citizens all, were mingling about with full glasses of fruit punch in their hands.
The old man grew worried about the drivers in the crowd, and any possible accidents and liabilities that might result from the party's only non-alcoholic option being suddenly spiked with booze. But Grandpa is a man of action. Instead of looking to prosecute, he reduced the impact of the crime by reducing the amount of alcohol in the fruity beverage. And he did this in a very interesting way.
Grandpa went to the kitchen and returned with two peeled English cucumbers which he sliced length wise into four quarters. He placed these four slices face down, rather decoratively, on the liquid surface of the punch bowl. Grandpa knew the peeled cucumber's flesh would absorb lots of alcohol about ounce per 10gram slice in ten minutes time.