TROUBLESHOOTING: WHY IS MY BROCCOLI CHEESE SOUP GRAINY OR CURDLED? This can happen if the temperature gets too high. Basically the proteins in the cheese tighten up and squeeze out the fat. You end up with a grainy, curdled consistency.
Sometimes an acidic ingredient, like wine, can prevent the soup from curdling. Slowly add the cream or milk and continually stir after adding. This will help prevent it from curdling. Use shredded cheese and always reduce the heat to about low to medium before adding.