When a tree is alive, sap is the tree’s lifeblood that carries nutrition from the roots to all areas of the tree, through its network of trunk and branches. When the tree has been cut, the sap is no longer needed and kiln drying the wood will result in the substance becoming crystalised; forming a resin.
When there are changes in humidity or temperature, it can be perfectly normal for small amounts of this resin to ooze from the timber, especially in its first year or use. The result can be rings of crusty white powder forming around knots in the timber. The resin is not harmful at all and can be easily removed.
After the first year of use, it is unlikely that any further resin will come out of the timber. Do remember though that timber is a natural product and its characteristics will change over time. This does not affect its strength or durability as a construction material however.
How to clean resin from timber
To remove the patches of resin from you timber, first remove as much as possible with a metal scraper. Next scrub the affected area with an oil soap and a stiff brush. Rinse and repeat if necessary. Acetone will remove any sticky residue still present on the timber.