The Little known Tradition of Sharing a Shot of Whiskey with the deceased at their Grave

When I was young my Grandfather Markowitz Passed  in 1968  and he was buried at the local St Johns Ukrainian Catholic Cemetery . 

 One day our whole family including my dads sister Marie  and her husband Eli joined us as we went to visit my grandfathers grave .
My Uncle Eli who is of Serbian Decent talked about coming out and visiting pap as he called him and pouring a shot of whiskey on his grave for him as they greeted each other .

https://en.m.wikipedia.org/wiki/Libation

He said it was an old tradition went back to the old country as a sign of respect for the dead .

While this is well known with Mexican Heritage on the traditional Day of the Dead to offer food and drink I did not know other cultures at time did this .
I have since learned not only is it a Serbian Tradition But also an Irish Tradition to pour the dead a shot of whiskey on tier grave,

I have actually been able to witness this tradition a couple times because I love to explore old grave yards and cemetery so if your ever lucky enough to witness the ritual of alcohol on a grave know it is of great respect