Espresso Spent Coffee Grounds as a Dough-Restructuring Agent in Composite Short Doughs: Workability, Shape Stability and Baking Performance of Functional Cookies

Spent coffee grounds (SCG) are a fibre- and polyphenol-rich by-product of coffee brewing. This study quantifies how replacing wheat flour with SCG (0–20% of the dough mass) modifies composite short doughs and the resulting cookies. The doughs were characterised by lubricated biaxial compression, spread-and-stickiness tests, oscillatory rheology and temperature-modulated differential scanning calorimetry (MDSC); the cookies by geometry, water status and colour. SCG increased the maximum biaxial extensional viscosity eleven-fold, reduced stickiness and shifted the thermal events of the sucrose–water, protein and starch domains. A closed-form constitutive model, combining a fractional viscoelastic element calibrated on the frequency sweeps with exponential strain hardening, reproduced the large-deformation curves of every formulation; the strain-hardening index was 1.64–1.89 up to 16% SCG and 1.21 at 20% SCG. The gravity number of the moulded piece (0.53–0.80) remained below the slump onset of a yield-stress material, and the mean footprint diameter of the cookies stayed within 3.3% of the control, so that the restructuring of the dough was expressed mainly as vertical development. Cookie thickness correlated with the peak spreading force of the dough (r = 0.90), and cookie moisture and water activity with the starch-melting temperature (r = 0.95–0.96).