Most people don’t realize that although a kiln can remove moisture from lumber at a very high rate, its real function is to control the drying rate, and in some cases, actually slow it down to prevent wood from cracking. Every species of wood has a maximum acceptable drying rate to keep if from developing defects and loosing its value. For example, white oak must be dried very slowly, only removing about 1% of its internal moisture per day. Walnut can be dried at 3% moisture removal per day and poplar can be dried at 10% per day.