Never, what does the vinegar do is my question. Almost any wild fruit or flower will ferment by itself as there is wild yeast on almost anything we touch and in the air we breath. I think I might be fermenting right now as we speak.
The vinegar and lemon juice contribute acids. Relying on the wild yeast and doing the primary fermentation in the bottle sounds risky to me. I would be more inclined to adapt the recipe to modern methods, using yeast, nutrient, and acid blend, etc.