WINETECH Technical Yearbook 2020

TABLE 1. Packaging used for storage of Sauvignon blanc wine.

Therefore, the containers that fared the best during the entire 18 months storage were the glass and PET multi-layer packaging. BIB also performed relatively well during the initial 12 months, after which an increase in oxygen was observed. The PET mono-layered packaging showed unacceptable oxygen uptake already during the initial stages of storage. The volume of the container also played an important role with the smaller volume containers taking up more oxygen. The wine volume to packaging surface ratio can play an important role in this observation and The decrease of sulphur dioxide is a useful marker for investigating the amount of oxygen consumed in wine (in a comparative way). An initial concentration of 30 mg/L free SO 2 was measured in the wine prior to packaging. As is often seen in the industry, a decrease in free SO 2 was observed three months after packaging. All treatments had an SO 2 concentration of around 25 mg/L with the exception of PETmulti (185) and PETmono (185) for which the concentration measured around 21 mg/L. From there on, the SO 2 content in the various treatments started to differ significantly. After six months, Glass (750) and BIB still had about 20 mg/L of free SO 2 after which the SO 2 content in the BIB should be considered. SULPHUR DIOXIDE

decreased to below 10 mg/L (already at nine months). The SO 2 in the Glass (750) remained stable for the remainder of the 18 month storage period. The concentration of SO 2 in the Glass (185) and PETmulti (750) hovered above 10 mg/L SO 2 from six months onwards, while PETmulti (185) and both PETmono were well below 10 mg/L. CARBON DIOXIDE LOSS In general, over the entire storage period, a decrease in dissolved CO 2 was observed. This can have a significant sensory implication especially for Sauvignon blanc wine resulting in a wine that is perceived as less fresh or even flat. The treatments all differed in their rate of CO 2 decline, however, it was evident that the glass The volatile thiols (aroma compounds responsible for the tropical fruit aroma in wine), declined during the storage period (3MH initial concentration 600 ng/L). After six months, Glass (750) had the highest concentration of 3MH at 500 ng/L. Surprisingly, PETmono fared relatively well and still had 3MH concentration of between 400 and 500 ng/L. The rest were all below 400 ng/L. After 18 months, all treatments were below 200 ng/L with Glass (750) and Glass (185) showing marginally higher values compared to the rest. bottles preserved the CO 2 best. AROMA COMPOUNDS

Container

Volume (mL) Abbreviation

Glass Glass

185 750 185 750 185 750

Glass (185) Glass (750)

PET PET PET PET

mono-layer (thickness 0.3 mm) mono-layer (thickness 0.3 mm) multi-layer (thickness 0.4 mm) multi-layer (thickness 0.4 mm)

PETmono (185) PETmono (750) PETmulti (185) PETmulti (750)

3 000

BIB

Bag in Box ®

RESULTS OXYGEN PERMEABILITY

• Glass (750), Glass (185) and PETmulti (750): The oxygen content decreased post-bottling and remained low (below 0.1 mg/L) during the entire storage period. • PETmulti (185) and BIB: The oxygen concentration was around 0.5 mg/L. The concentration remained low during the storage period, however, at 18 months, the dissolved oxygen content of the wine in the BIB spiked to around 1.8 mg/L. • PETmono (750) and PETmono (185): Oxygen concentrations increased to around 1 mg/L and 2.3 mg/L respectively after three months’ storage. Concentrations then remained stable with a further increase in oxygen observed for PETmono (185) after 18 months.

Oxygen can permeate through the container and dissolve in the wine, however, it is important to remember that while this permeation occurs, dissolved oxygen is consumed by wine components initiating oxidation reactions. The rate at which the oxygen permeates and dissolves in the wine, and the rate at which the dissolved oxygen is consumed by wine components, will ultimately determine the amount of oxygen present in the dissolved form. Therefore, if the rate of permeation is higher than the rate of consumption, the dissolved oxygen in the wine will increase over time. The initial oxygen measurement of the wine was 0.73 mg/L. After three months’ storage, the oxygen concentration was as follows:

WINETECH TECHNICAL YEARBOOK 2020 150