What causes greasy and heavy choux pastry?

Greasy and heavy choux pastry can result from using too much fat or not properly incorporating the ingredients. If the butter is melted too quickly or if the flour is added before the mixture reaches the right consistency, it can lead to a dense texture. Additionally, insufficient cooking of the flour and water mixture can prevent proper steam formation, which is essential for achieving the light, airy structure characteristic of well-made choux pastry. Finally, overmixing after adding eggs can also contribute to a heavy product.