'Fabulous Oxtail' Doreen Randal, recipezaar, with plum jam, says add vinegar but not what kind or amount, help

1 and a half teaspoon

'Fabulous Oxtail' Doreen Randal, recipezaar, with plum jam, says add vinegar but not what kind or amount, help
Inca...I'm writing to Doreen, who posted that recipe..I'll find out exactly.