We're working with some 16th century recipes for sauces that call for blood (among other things). However, several members of the group try to keep kosher, and besides, I have no idea where or how one would acquire blood for cooking.  I know I can substitute egg for the protein/thickener aspect, but what about the flavor? What does blood actually taste like (when cooked)? I've had blood sausage, but all I remember about its flavor is the generous quantity of black pepper. Would a red wine and some salt come anywhere close? 
Depending on the animal, blood would impart a somewhat metallic taste and a certain “richness” - not really the umami-meatiness of red meat, more like the earthiness of liver - with a slight sweetness.   The flavor profile will be quite different depending on the animal, with pork being more neutral than the more intense and metallic beef.  A substitute would depend on the recipe. But the acidity of red wine is very much not what blood would contribute to a dish. If the binding properties are to be ignored, think “beets plus sautéed mushrooms”, as a very, very vague flavor approximation. But if your sauce is rich per se, you can probably just skip the blood without doing much culinary harm. 