The following expression was used in an old baking book, "The Modern Baker, Confectioner and Caterer" (1907) by John Kirkland:
The bad results so frequently obtained are generally due to the method of cooking. If the batter is in the least degree too stiff" the muffins are certain to be " blind ".
What state of muffins is expressed to be "blind"?
The book is accessible online here and the above expression is found at page 153 (an original book page).
Thanks in advance.