Fresh, raw cashews are as prized in the wild as roasted cashews are in cultivated culinary circles -- so much so they're locked away in shells rife with allergens, irritants and other poisonous compounds. Raw cashews undergo cleaning and a brief roasting to neutralize their noxious oils, but it doesn't rid them of another undesirable: tannins. Harmless but no less distasteful, raw cashews have an astringency that borders on acridity, and they need purged of tannins before cooking.
Rinse the cashews under cool running water for several minutes -- a sieve or mesh strainer works well for holding the nuts. Next, cover the cashews in 3 to 4 inches of cold water and let them stand for at least 2 hours, but as long as overnight. Rinse the cashews and let them air dry before roasting.