The following factors could prevent egg whites from stiffening when beaten: Residual Fat: Even a tiny amount of fat from yolks or grease on bowls can hinder the egg whites from stiffening, so ensure utensils and bowls are completely clean and free from any residue. Separate your eggs carefully, making sure no yolk is present. Room Temperature: Cold eggs take longer to whip and might not reach stiff peaks. Allow the eggs to come to room temperature before beating.. Older Eggs: Fresh eggs tend to whip up better than older ones. The protein structure in older eggs might weaken, keeping the egg whites from stiffening.