Mitigation of Brown Stain in Ponderosa Pine Shop-Grade Lumber Using High Temperatures Early in Kiln Schedules

Abstract

ABSTRACT Brown stain makes the appearance of ponderosa pine shop lumber look dark, streaky, and splotchy, which often results in lumber downgrading. When brown stain occurs in a piece of shop lumber, it is often sorted separately and ultimately sold for a discount. Manufacturers of ponderosa pine shop lumber have adopted low-temperature dry kiln schedules to mitigate brown stain effects. The low-temperature schedules are lengthy, often taking more than 100 hours of drying time. Preliminary high-temperature (>212°F [100°C]) drying schedules have reduced drying time while minimizing brown stain effects. The purpose of this study was to further explore drying schedules with high temperatures early in the schedules followed by conventional drying settings. Results showed that 10 hours of initial high-temperature drying can be used without brown stain affecting the visual grades of ponderosa pine shop lumber while reducing drying time up to 17 percent.