Chemical Brown Stain in Sugar Pine

The primary cause of brown stain in sugar pine is sugars and related substances contained in the sap. These sugars come to the surface during drying, evaporate, and result in discolorations. Both pentoses and hexoses yield dark colored products when heated, and the degree of discoloration is increased by the presence of amino acids. Color formation is accentuated by increasing temperature, time, concentration of reactants, relative humidity, and by increasing pH values. Furan derivatives are believed to be the primary reaction products of sugar decomposition. Freshly cut and rapidly processed sugar pine lumber does not stain under ordinary kiln conditions unless high temperatures are employed. The use of sulfur dioxide-producing chemicals as stain retardants does not appear promising. Fifty-six references are included.

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