Maple Color and Drying Conditions

      Maple can turn gray as it dries. If you want white wood, you have to carefully control the kiln conditions. July 30, 2007

Question
This is my first winter drying lumber. I have noticed when drying maple, my middles are turning a grayish to brownish color. What is the cause of this and what can I do to stop it?

Forum Responses
(Sawing and Drying Forum)
From contributor D:
I don't know where you are or what the weather is, but if you want really white hard maple, it should be in the kiln as soon as it is sawn. And the logs should either be kept cool or sawn as soon as they are down. One customer keeps his maple logs cold in a refrigerated trailer in the summer.



From the original questioner:
I am in Wisconsin. I had heard that when the lumber is sawn and it freezes and then it is placed in the kiln, caution needs to be taken on the starting temp. I normally start my white schedule at 105 DB with the steam off. Now, if lumber is frozen, are there special precautions I need to take when starting? Does frozen lumber create color issues? I had thought that a defrosting method was bad to do. As far as the logs sitting, that I am clueless on. I do know, however, once it gets in our yard, it is immediately put on sticks. Some homework for me perhaps. Thanks for any help you can provide.


From contributor L:
Contributor D, how much more difficult is drying hard maple than hickory with plenty of sapwood and keeping it bright? I purchased some hickory (a pickup load) a few years ago in August. I'm in OK, and blew air across the load in my shop for several weeks; worked well. We have a few sugar maples over here and might try some someday.


From contributor D:
Hickory that is used for drumsticks must never see temperatures over 120F. However, hickory for flooring and furniture is usually dried at higher temps and allowed to color. As for hard or sugar maple, you start at a low temperature.

Color in maple is affected by temperature mostly, so frozen is not bad. Just thaw it at a low temperature and as soon as the drying starts, shoot for 5% a day. Make sure your equipment matched up with what you plan to do.



From Professor Gene Wengert, forum technical advisor:
I would add to the thawing comments, that you should make sure that the RH is correct from the moment the fans are turned on. Get the correct RH and then raise the temperature as fast as you can to the appropriate level (105 F), keeping the HR at the correct level. Do not use something like 80 F and 90% to 100% RH unless poor colored maple is what you want.

Gray in the middle indicates slow drying at warm temperatures. Perhaps the air drying was okay, with good RH and cool temperatures, so you got good outside color. Then in the kiln, you had the RH too high so the core stained (enzymatic oxidation stain, and not fungal). Maybe you had too much maple in the kiln for its capacity, so the RH was too high initially. Air flow is also important... special maple kilns use 600 fpm or better.

We will have a special session at the GLDKA meeting this March talking about maple color. The meeting is in Wausau, WI... Are you close?



From the original questioner:
That sounds along the same lines as I was thinking. I am attending the Memphis class 12th - 14th, and will also see you in Wausau the 29th and 30th. Thanks!

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Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Primary Processing

  • KnowledgeBase: Primary Processing: Air Drying Lumber

  • KnowledgeBase: Primary Processing: Kiln Operation


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