Adding oenological tannin vs. overripe grapes: Effect on the phenolic composition of red wines

• Addition of oenological tannin may solve deficiencies in flavanol and pigment contents.
• Use of overripe grapes might contribute to the stabilization of the colouring matter.
• Synthesis of vinylphenol-type pyranoanthocyanins is promoted in overripe wine.
• Synthesis of Vitisin A is promoted in Tannin wine.
• Both oenological treatments lead to darker wines (lower L* values).

The effects on the phenolic composition (flavanols, phenolic acids and anthocyanins) and on CIELAB colour parameters of two different oenological practices (adding oenological tannin, using overripe grapes), whose purpose is to compensate wine quality deficiencies, have been evaluated in red wines made from Tempranillo grapes in two consecutive vintages. Both the addition of oenological tannin and the use of overripe grapes generally increased hydroxycinnamic acids and pigment contents. However, the effect of the former was noticeable above all in early stages of winemaking and ageing, whereas the effect of the latter was observable in late stages of ageing. In general, flavanol content increased in wines treated with oenological tannin, and decreased in wines made from overripe grapes in relation to control wines. Colour differences (ΔE*ab) between control and treated wines were in some stages higher than 3, indicating that the colour modifications caused by both treatments can be detectable by the human eye. Results showed that the addition of the oenological tannin to wine will be useful to address deficiencies in flavanol and pigment contents, whereas the use of overripe grapes will be useful when colour stabilization is required.