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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Yellow Streaks in Claro Walnut After Kiln-Drying 
Question
I use a Nyle L200 kiln unit. The bulk of the customer's wood is 8/4, with a couple of 12/4 pieces. He also brought me about 300 bd ft of black walnut, also 8/4. The customer's wood initially measured between 20 - 30% MC (both claro and BW). After several weeks in the kiln at 120F and 40% RH, the MC% in the claro wood varied between 6 - 20% - in the same board! Some of the claro boards had a graft line, and in these boards the English walnut above the graft line also came out consistently in the 6 - 8% range. The black walnut - which was interspersed in the same stacks as the claro in the same load - came out uniformly between 6 - 8% MC. After a couple of weeks with varying results, we unloaded the kiln and the customer planed down the claro to find yellow streaks throughout the wood. These streaks corresponded with where there was higher MC%. (See photo - the yellow streaks are not sapwood). Interestingly enough, the yellow wood is buried in the boards; the surface is a uniform brown color. It is only after planing the surface off that the yellow wood is exposed. The kiln stacks were all measured with an anemometer for proper air flow, and my equipment is working properly. Is this a common problem when drying claro walnut? Are there any special techniques that I should follow in order to successfully dry this wood?  You can see where the yellow streaks are embedded in the wood - primarily in the center of the boards.  Forum Responses
The moisture problem is called a water pocket, wetwood, or bacterial wetwood. The high moisture is more common with thicker stock. The cause is a bacterial infection in the tree. It cannot be fixed, so drying must be very slow. In fact, air drying for 6 months or more is suggested. Avoid sawing 8/4 and thicker from such logs. After drying, it is common to find cracks in this wood, as it is weaker than normal. If you use the wood before it is dried, then the moisture will leave eventually and the wood will shrink at that time.
From the original questioner: Gene, as always, thanks much for sharing your insight. Any suggestions as to a good targeted daily MC% reduction rate to use considering the bacterial infection in the wood? From Professor Gene Wengert, forum technical advisor: As you have noted, the bacterial wood has not dried much at all, so the drying rate is close to zero. From contributor J: Would like to know if the bacterial infection can be detected (without much due process) in the green wood. We dry with a kiln other than the Nyle and have the same problem From Professor Gene Wengert, forum technical advisor: If the high initial MC or the odor or the shake are not present, then it is difficult to detect ahead of time. Have you reviewed the related Knowledge Base areas below? 
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