Eggs are another common ingredient in meatball recipes. Because they’re so rich and flavorful on their own, many cooks assume that the role of eggs is to lend fat, flavor, and moisture to the finished meatballs. But while eggs do contribute moisture to the initial meatball mixture, most of this will evaporate by the time the meatballs are cooked. Most meatball recipes depend on other ingredients, such as herbs, cheese, and the meat itself for flavor.
Instead, eggs serve a more prosaic function: to help hold everything together. As the eggs cook, their proteins coagulate and solidify, binding all the other ingredients they contact. In effect, they act as a form of edible glue.
Because the role of eggs in meatballs is primarily structural, the amount of eggs you use does matter. You want enough to keep the mixture stable and easy to handle, but too many will make the mixture overly soft. Excess eggs will also make meatballs tough and spongy, rather than toothsome and tender. A good rule of thumb is to add one egg per pound of meat.
