In a clean, wide-mouth container, combine equal parts unfiltered cider vinegar with unpasteurized cider, filling only to widest part of the jar. Cover with cheesecloth and let sit in a cool, dark spot for several weeks. The vinegar mother will begin to form and float on the top.
Taste the vinegar by gently moving the mother aside (it’s ok if it sinks). When the vinegar tastes nice and strong, it is ready. Strain almost all into a jar with a narrow neck and seal tightly.
Save the mother in the remaining vinegar and start the process all over again with a wine, cider, beer, or fruit of your choice. (This time you will not need the unfiltered cider vinegar because you have made your own mother.)