How much vinegar can I safely add to bread dough?
Cool Russian Black Bread!

Since you gave an update I figure you might still be tracking the question.

Does your recipe use Baking Soda? That would react to your vinegar to create the CO2 needed to rise the heavy bread, but since it is a very fast reaction you would need to go from adding vinegar to oven in a matter of minutes.

I'm guessing the recipe uses yeast instead and that the vinegar is merely for a strong sour taste. I would think that much vinegar would inhibit your yeast, but since you got a good springy baked bread you are already on the right track.

Some traditional recipes rely on a sourdough starter where the yeast does the rising and the bacillus bacteria is teamed up to convert the milk's lactose into that tangy sour lactic acid instead of vinegar. You could create your own "wild yeast" by mixing your flour (rye &amp; wheat) with buttermilk or yogurt with an active bacteria culture and adding commercial yeast (or praying to capture and grow your own wild yeast which can take a lot of time and will probably be the same yeast species based on the Sourdough Project tests).