I did a search and found this. However, I confess that I find the explanation a bit confusing.
Ted, from Bangkok, Thailand tells us, "Apple Cider Vinegar in itself is alkaline because of its "ash" content, which means if the apple cider vinegar was burned, what is left over becomes ash. When you check for the pH of that ash and dissolve it with water, the content is alkaline. Whenever our body digests anything it undergoes oxidation, which is similar to burning and the end result is that you can determine whether the end product was alkaline or acid. Apple Cider Vinegar has anti-fungal, anti-bacterial, and anti-viral properties, primarily coming from the malic acid and acetic acid portion of the vinegar. Apple cider vinegar acts as a buffer in the body because the acetic acid reacts with base or acid compounds to form an acetate, therefore rendering them chemically bioavailable for the body's utilization. Additionally Apple Cider Vinegar can reduce the toxicity of certain compounds by converting the toxin into an acetate compound which is less toxic. This is why they are ideal for insect bites and certain skin allergies. While Apple Cider vinegar in itself is considered alkaline, a chemically pure vinegar (acetic acid) is neither acid nor basic forming as it leaves no ash as the entire portion, when burned evaporates complete