Apple cider is usually too sugary for the yeast to grow properly. If you want to try to omit the water to make a stronger cider mix, be sure to proof the yeast first. We used home made unprocessed apple cider for these and they had a nice cider taste.
While we have made extra batches of these for sharing or to have on hand for a quick dessert, we usually skip the jar and just make a batch of these fudgy brownies.