Combine the sweet potato, apple, cranberries, lemon juice, starter culture, Sucanat, spices, and salt in a medium-size bowl. Mix thoroughly.
Transfer to a quart-size fermentation vessel. The brine should come at least 1 inch above the level of the sweet potato mixture. If it doesn’t, weigh the pieces of fruit and vegetables down with ceramic weights or another clean object. Seal the jar with an airtight lid or a lid with an airlock system. If using canning jar lids, be sure to “burp” the jars as needed during fermentation.
Place jars in a space that maintains a cool room temperature. Allow to ferment 2 to 4 days, or until bubbly and fermented to your taste, before transferring to cold storage.