Apple cider vinegar is that vinegar which is made up of apples (guess all know that). To be precise it is made up of fermented apple juice. Apples are cut in small pieces and covered with water and leave them in room temperature. This will make the sugar which is present in apple to ferment and turns it to alcohol. This apple cider vinegar is fermented twice once to make alcohol and second time to make vinegar (acetic acid).