Most of the soft maple, both red and silver leaf, that we have been drying ends up having dark core and white shell. I have a 100-87.5 start with a gradual temp increase and EMC decrease and about 450 fpm across the load. This has been found in air dried, partially air dried and green off the saw. I have followed the suggestions in "Drying Hardwood Lumber" for reducing chemical stains, but it does not seem to make a difference. Does anyone have suggestions?
In these same soft maple charges, we are getting occasional boards that are grey. I think that these are probably log or pre-stacking problems. Is this correct?
(Sawing and Drying Forum)
The dark core in maple is from not getting the lumber dried quickly enough. The dark core can also be accentuated by too high temperatures in the kiln. High air flow, low kiln temperatures and low EMC's will help combat the problem. I believe that this will take care of your grey boards, as well. One other thing - are you getting the settings that you think you are in your kiln? It never hurts to check the calibration of your kiln controls.