Evolution and Stability of Post-Fermentative Copigmentation in Listán Negro Red Wine Using Caffeic Acid and Glucose

The Listán Negro cultivar, a red grape variety endemic to the Canary Islands, has been traditionally characterized by limited color stability, often leading to significant pigment loss during early storage. The present study investigates the efficacy of caffeic acid as a hydroxycinnamic cofactor for copigmentation when it is introduced during the post-fermentative stage in young, lightly colored red wines. Ninety young red wine samples were prepared using a factorial design. Caffeic acid was added at four concentrations, both independently and in combination with glucose, and was monitored over 158 days. Initial spectrophotometric analysis revealed a dose-dependent hyperchromic effect, with color intensity increasing by up to 12.8% for caffeic acid alone and 15.9% when combined with glucose. Accompanying bathochromic shifts (1–3 nm) were consistent with copigmentation interactions. Although the effect decreased over time at lower concentrations, doses ≥ 480 mg/L maintained improved color retention after storage. The addition of glucose alone did not improve color stability and showed a transient chromatic response. These results indicate that post-fermentative addition of caffeic acid provides a short-term enhancement of color intensity in low-anthocyanin red wines; however, this effect is strongly concentration-dependent and decreases over time, thereby identifying a threshold for persistent post-fermentative copigmentation.