Darkening Problem when Heating Ash to Kill Borers

Dry the wood first, then heat it, says the Wood Doctor. July 29, 2011

Question
We have to heat treat our ash before it comes out of the kiln due to the emerald ash bore. I heat treat it at 170 degrees for 5.5 hours with an EMC of 7.5. This is the only way to ensure that it gets heat treated for the government regulations. I have just received a small complaint that our ash is starting to Carmalize and the color isnít as good as it was in the past. The only thing I can think of is that during this process it is doing something to my wood as I havenít changed anything else with the schedules that we are running. Can anyone shed some light on this?

Forum Responses
(Sawing and Drying Forum)
From contributor D:
Why 170F? You don't need to heat the wood that hot to kill the bugs unless your customer is insisting on it


.
From the original questioner:
We need 170 because we need to have a wet bulb of 140 degrees and kept there for 5.5 hours. To get that I need to have the temp high as I donít want to put too much moisture back in the kiln. If I was at 160 degrees I would need a 9.0 EMC for 5.5 hours and feel that may be too much and would actually allow the lumber to gain too much moisture. What do you think?


From Gene Wengert, forum technical advisor:
Many species, when wet and heated that hot, will turn darker. There is little chance of going cooler, but anything over 140 F will add a lot of colorization. For this reason, ash is dried normally and then at the end of the cycle, when the wood is dry, the wood can be heated without color loss.