Prepare the fruit (core apples, remove unwanted seeds or skin, etc.) and cut into pieces.
Process the fruit in a blender, food processor or through a food mill until the mixture is smooth.
Mix in the salt, spices and sweetener, to taste.
Prepare the starter culture according the instructions that came with it, then mix it into the fruit mixture. If using whey, add it now.
Place the fruit mixture into a canning jar, leaving 1-2 inches of headroom, and place a fermentation lid on the jar.
Wrap the jar in a towel to block out light and allow the jar to sit in a warm spot (70-80°F) for 7-10 days.
Be careful when removing the jar lid, because pressure may have built up.
Drying the Fruit Leather:
Line dehydrator trays (or baking sheets if using the oven) with sheets of unbleached parchment paper or silicone dehydrator sheets.
Spread the fruit mixture evenly and very thickly on the sheets. If the mixture is too thin, strain it through a nut milk bag, tea towel or tight weave cheese cloth to thicken it up. The strained juice is delicious and contains beneficial bacteria from the culturing process.
Set your dehydrator (or oven) for 110 degrees and allow the fruit leather to dry for 8-24 hours. (Don’t set it any higher than 110, or you’ll kill the beneficial bacteria you just cultured!) The exact length of time will depend on the thickness of the mixture, so be sure to check on it regularly.
The fruit leather is done when it is no longer sticky.
Peel the leather away from the parchment or silicone sheets and tear it into strips.
Store in an airtight container and keep in the fridge for lasting freshness.