Parboiling. Parboiling is the partial boiling of food as the first step in the cooking process. The word is often used when referring to parboiled rice. Parboiling can also be used for removing poisonous or foul-tasting substances from foodstuffs.The technique may also be used to soften vegetables before roasting them.arboiling is the partial boiling of food as the first step in the cooking process. The word is often used when referring to parboiled rice. Parboiling can also be used for removing poisonous or foul-tasting substances from foodstuffs. The technique may also be used to soften vegetables before roasting them.