I have seen several recipes calling for black walnuts. What is the difference between them and the walnuts that are usually found in grocery stores? —J.W., Niles, MichiganThe walnuts found in the grocery store are mild-tasting English walnuts. They have a semi-firm light brown shell. Native American black walnuts have a very hard thick black shell. The flavor is richer and more intense than the English walnut. Because black walnuts are difficult to shell, they are not as widely available commercially as English walnuts.