Gluten is a protein and is found in grains such as spelt, wheat and rye.  Gluten is a useful when making bread and pasta as when the flour (which contains gluten) is mixed with water, it creates a glue-like “sticky” consistency, making the dough strong and elastic.  It gives bread a delicious chewy texture. Salt also helps to preserve the strength of gluten. 

On the other hand, when butter is added to a dough mixture, it shortens the strands of gluten, making the dough “short”.  Butter contains fat, and the fat weakens the strands of gluten, so they can’t join together to make a strong elastic dough.  This is why butter is added to dough such as brioche, short pastry or baking which require a soft tender mixture.

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