The bacteria causing fermentation require some form of sugar to feed on. Sugar alcohols, allulose, and stevia will not feed the bacteria. Fruit, vegetables, and (lactose containing) dairy have enough natural sugars to feed the fermentation but animal protein ferments (such as corned beef) and water kefir need added sugars. Plant protein (nuts and seeds) ferments such as almond milk yogurt also need added sugars to balance the bacteria and the yeast (a fungus). (Yeast readily feeds off of the sucrose in nuts and seeds while bacteria does not.) When sufficiently fermented, all of the sugars are consumed by the yeast and bacteria. Alternative sweeteners can be added after fermentation.
Difference between yeast and bacteria.
Ginger bug recipe. Ginger beer recipe.
Fermented root beer recipe.
Rejuvelac recipe.
Fermented nut milk recipe.