It's already cooked. Might depend on what you are putting in there with it though. Your best bet is to add it in the last hour of cooking. "Milk/Cheese Milk, sour cream, and cream break down over long periods of cooking, and should be added during the last hour. Condensed cream soups are good substitutions for milk and can be cooked for extended times. "Healthy," or reduced fat cream soups can be used in any recipe as a substitute." Here is a potato soup recipe that tells you how they do it in a crock pot. I think your clam chowder would be similar. "Crock Pot Potato Soup Portions: 8-10 Ingredients: 6 potatoes, peeled and chopped 2 leeks (optional), chopped 1 large carrot (or 10 baby carrots), chopped 1 stalk celery, chopped 2 onions, chopped 5 cups water 1 T. salt 1 T. parsley flakes 1/3 cup butter 4 chicken bouillon cubes 1 can evaporated milk Instructions: 1. Put all ingredients except evaporated milk into crock pot. 2. Cook low: 10-12 hours, high 3-4 hours 3.