The Amish make vinegar from what's available — apples, pears, grapes. Simple process: sugar → alcohol → vinegar.
Recipe
Apple scraps (peels, cores) fill jar 2/3. Cover with water. Add 1 tbsp sugar per liter. Cover with cloth (not lid — needs oxygen). Dark place, room temperature.
Stage 1: Alcohol (2 weeks)
Wild yeast on apple skins converts sugar to alcohol. Stir daily. After 2 weeks — strain, remove pulp.
Stage 2: Vinegar (4-6 weeks)
Acetic acid bacteria (Acetobacter) convert alcohol to acetic acid. A 'mother of vinegar' may form — a slimy film. Normal and helpful — it speeds the process.
Doneness
Taste — should be sour with no alcohol taste. Strain, bottle. Stores indefinitely — vinegar doesn't spoil.