I have a vinegar based bar-b-que sauce recipe that calls for 3% acidity vinegar which cannot be found. How do I cut 5% vinegar to 3%?
Cut it with water.
Commercial white vinegar is basically nothing but water and acetic acid.
3 units of 5% vinegar and 2 units of plain water give 5 units of 3% vinegar.
You asked for a formula
Let X bet the amount of 5%
The amount of water you need to add is
5/3*X - X = 2/3*X
So if you have 6 cups
2/3*6 = 4 cups to add