Two to three hours. Poplar trunk beans have less water, so soaking them in cold water for 2 to 3 hours will help to remove the bitterness inside the dried beans and make them easier to cook. White lentil, whose scientific name is white lentil, is full, neat and shiny, and has the functions of reducing blood fat, promoting fracture healing, beauty beauty, slimming, antibacterial and antiviral.