You know Romaine, Butterhead, Crisphead are at their freshest when this "milk" (lactuca sativa) releases when cut. Full of folic acid, potassium and Vitamin K. If it's not milky, it's not fresh. A lettuces nutritional value begins to break down right after it is cut. Always tear or cut the leaves just before dressing and serving to reserve the nutrients. NEVER buy pre-cut bagged lettuce. Its pointless.