This review will focus on traditional sparkling wine (TSW) phenolics and how the production process influences them.

Introduction

TSW vinification is comparable to that of white wine due to the light pressing of the grapes, minimal skin contact and no maceration. There is very little phenolic extraction, and generally, very little phenolic content is both expected and desired. Since high phenolic content is linked to reduced ageing capacity and browning in TSW, phenolics are kept low throughout winemaking. Early harvesting, whole-bunch and light pressing minimise phenolic extraction.

Temperature can greatly affect the extraction of phenolics from grapes. Changes in temperature at pressing, during fermentation and storage has been shown to affect the phenolic composition of table wine. In white wines, because the phenolic content is low, there’s little contribution to the taste and mouthfeel.

Overview of the TSW winemaking process is given in the Part 1 (Sensory perception of traditional style sparkling wine) of this series.

Factors influencing the phenolic content of traditional sparkling wine

Viticultural practices, such as vine spacing, pruning and other canopy management techniques which influence the amount of sunlight exposure to the berries, have been linked to changes in the phenolic composition of grapes. Soil, climate and irrigation influence berry yield (and hence the phenolic levels), but the composition and distribution of phenolics throughout the berry is essentially the same. Moreover, different clones have different berry sizes and maturation rates hence may yield different concentrations and compositions of phenolics.

TSW winemakers do not desire a high phenolic content, therefore they harvest early when the phenolic maturity is low, gently press the grapes resulting in even lower phenolic concentrations in the juice. Thus TSW tend to have lower phenolic concentration compared to table wines.

Phenolic composition of traditional sparkling wines

Grape-derived phenolic compounds can be categorised into two main groups, namely non-flavonoids (colourless compounds, for example hydroxycinnamic and hydrobenzoic acids) and flavonoids (for example anthocyanins and tannins). Flavonoids are located mostly in the skin and seeds, non-flavonoids are more concentrated in the flesh. In TSW elaboration, mostly non-flavanoids are extracted into the juice upon pressing, flavonoids are extracted to a lesser extent.

Total phenolic content of TSW are within the range reported for white wines (i.e. 50 - 350 mg/ℓ GAE) with hydroxycinnamic and hydroxybenzoic acids being the major component. Studies have found a decrease in total phenolics from base wines, after the second fermentation and throughout ageing, whilst one study found an overall lack of change in phenolics from base wines throughout nine-months ageing. Our recent study on the evolution of phenolics throughout MCC winemaking also found an overall lack of change in the phenolics; see Part 4 (The truth about chilled MCC grapes).

Conclusion

Minimum phenolic extraction is the goal of TSW winemaking. Mainly hydroxycinnamic and hydroxybenzoic acids are extracted, present at low concentrations and below the sensorial limit of detection. Given the current research on TSWs internationally, there is a gap in scientific knowledge on the South African MCC. The effect of grape temperature on the phenolic extraction of MCC has recently been explored; see Part 4 (The truth about chilled MCC grapes).

– For more information, contact Francois van Jaarsveld at [email protected].