Ask Proctor: The North American Maple Syrup Producers Manual. The Maple Digest 58(3): 26. By Perkins, T.D. and van den Berg, A.K. By Web MasterMarch 1, 2025Other Publications Ask Proctor: The North American Maple Syrup Producers Manual. The Maple Digest 58(3): 26. By Perkins, T.D. and van den Berg, A.K.