The use of vinegar is frequently written about on this forum for use as a soil acidifier. Below is the results of research at Minnesota University.
Dr. Jeff Gillman PhD
Department of Horticultural Science
University of Minnesota
After research on vinegar as a soil acidifier by Dr.Gillman, he stated "In a nutshell, it just doesn't work well at all. It takes a lot of vinegar to change the pH, and the change is really very brief.