Leaving aside the fact that you might have added milk, oil or seasoning, the different taste comes partly from whether the egg has been beaten. Egg white is less flavoursome than the rich, fatty yolk, so mixing them will change the sensory experience.
Browning a fried egg or omelette also changes its taste. This is down to a chemical reaction between proteins and glucose called the Maillard reaction, which creates colour and gives the egg a slightly nutty flavour. Finally, a large part of flavour perception comes from the food’s texture, or ‘mouthfeel’. So this is another factor in why silky scrambled eggs taste slightly different to a gooey poached egg or a fluffy omelette.
Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.