Take the whole garlic bulbs and slice the stalk off, exposing the tops of the cloves.
Peel back the white skin of the garlic down to the thin pink layer covering the raw garlic cloves.
Add the garlic bulbs, whole if you can, to the jar. Break them down if they can't fit through the jar opening. Fill the gaps with the separated cloves.
Once you have filled the jar (there will be gaps so don't worry about that), add red wine vinegar until it fills half the jar, then add your balsamic. Push down the garlic cloves and squeeze in more if you can. Fill up with more balsamic vinegar if you have space.
Add the salt and close the jar. Tilt the jar up and down gently to mix the vinegars and salt.
Leave in cool dark place like a pantry for at least 1 year. Once opened store in the fridge.