Q: There is a debate going on at our lumber yard between the salesmen and the kiln operator. Is it true that winter cut northern Michigan hard maple is whiter than summer cut? I have heard a couple of the old timers say that back in the good old days they had a rule that you don't cut hard maple if the leaves are on the tree. The reasoning was that in the summer the sap is in the tree making the wood a caramel color. In the winter the sap would no longer be in the tree, making it a nice white color. Is there any validity to this?
A: There is indeed truth to what they are saying about winter-cut being whiter than summer cut, but the reason for this occurring is incorrect. The reason that this happens is that the discolor reaction requires warmth. In the summer it is warm enough for the reaction to begin occurring in the log after the tree is harvested and in the lumber after the lumber is sawn. In the winter it is not warm enough for the reaction to occur prior to entering the kiln. However, if you mistreat the lumber in the kiln by using 90 percent RH or higher at 90F or warmer for 24 hours, you can discolor winter-cut lumber. If you use temperatures over 125F early in drying, you can also cause the lumber to turn pinker or browner.
Incidentally, the sap content is the same year-round; it is only that in the spring and summer the sap is flowing.
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