Spraying champagne has become a key part of the podium revelry as the prize recipients (First, Second, Third and Constructors) celebrate their success. Usually spraying each other and showering their teammates below before passing the bottle around for a celebratory drink.
There are a few theories on this but the first recorded instance in F1 was Sir Jackie Stewart when he placed his thumb over the bottle opening to try and stop wastage. The rest is history...
I was the first person to spray champagne in Formula One
Sir Jackie Stewart