Juices can be used to extend your fasting period. If you normally break your fast around noon, you can use a juice at that time to ease your hunger and give you an energy boost, so you can fast for a couple more hours. That juice won't activate the digestive system because the fiber has been removed. A juice fast usually lasts 1 to 10 days.
There are different methods for following a juice fast. Some fasts will tell you to drink only freshly squeezed juice, while others allow you to eat more food during the fast. Fasting apple cider vinegar alone is not a good idea, since it doesn't provide the body with a full range of necessary vitamins and minerals. Unfiltered apple juice is a much better option, as it contains a little bit of fiber along with vitamin C.
Juices without added sugar, artificial colors, or flavors provide pure nutrition without the chemical additives you're trying to avoid. Fruit juices are high in natural sugars, so it's a good idea to add protein, such as yogurt, to a liquid diet to help slow the insulin response.