Linda Carucci on Basil Pesto

"To help preserve the bright green in the fresh basil, chill the olive oil before adding it to the food processor. (The cold oil mitigates some of the heat from the processor.) Some cooks add a crushed vitamin C tablet or a little ascorbic acid to preserve the color. Others pour a thin layer of oil on top of the pesto before storing."
— Linda Carucci, Cooking School Secrets for Real World Cooks