Use of Membrane Ultrafiltration for Wine Stabilisation and Clarification
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(Thesis)
Date
2021
Authors
Sui, Yihe
Editors
Advisors
Wilkinson, Kerry
McRae, Jacqui
Muhlack, Richard
McRae, Jacqui
Muhlack, Richard
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Thesis
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Abstract
The clarity and stability of white wine are critical to conventional white winemaking.
Consumers generally regard the presence of haze in bottled white wine as an indication of
poor quality. Winemakers routinely add bentonite (a kind of clay) to wine prior to bottling
to remove the proteins responsible for haze formation to ensure the wine remains clear and
transparent. However, there are both wine quality and financial implications associated
with bentonite fining. In order to improve white wine quality and mitigate the issues
arising from bentonite addition, researchers have endeavoured to develop effective
alternatives. Ultrafiltration (UF) technology has been used extensively in the food industry
to concentrate or separate macromolecules, and has the potential to be applied to wine as
an alternative approach to protein stabilisation. Protease addition to juice, coupled with
heating, was shown to be an effective process for removing proteins, thereby offering a
feasible alternative to bentonite for protein stabilisation. The research presented in this
thesis aims to evaluate and validate a combination of UF, heat and protease treatments as
an innovative approach to achieving protein stabilisation in white wine.
The thesis commences with a review of scientific literature related to: the mechanism and
influencing factors of wine haze formation; the theory and limitations of bentonite fining;
and the alternative protein stabilisation strategies evaluated to date. The methodologies
employed to predict wine haze potential are also briefly outlined, along with the use of
membrane technology in winemaking, and a summary of membrane fouling issues
(Chapter 1).
A study involving membrane characterisation and optimisation of UF, heat and protease
treatments is reported in Chapter 2. Briefly, pilot scale UF treatments were performed on
two wine samples using a 10 kDa nominal molecular weight cut-off membrane, and gave protein stable permeate and protein concentrated retentate. Targeted protein removal from
retentate following UF enrichment using heat or heat and protease treatment was
subsequently optimised. Heating retentate at 62°C for 10 min (with or without protease
addition) achieved significant protein removal (30 – 96%, depending on the initial wine
protein composition). Semi-commercial scale trials were therefore conducted on a third
wine to confirm the performance of UF and heat and/or protease treatments.
Recombination (blending) of treated retentate with permeate delivered wine that was
almost heat stable, such that significantly less bentonite addition (~50 – 60%) was required
to achieve complete heat stabilisation of the wine.
The impact of the combined UF/heat/protease treatments on the heat stability, volatile
composition, sensory profiles and quality of white wine formed the basis of a second study
(Chapter 3). Treatment effects on wine composition were determined by analysis of
varietal, fermentation-derived and oxidative volatiles using gas chromatography-mass
spectrometry, while sensory profiles were determined using the Rate-All-That-Apply
analysis and wine quality scores by an expert panel. Wine treated by a combination of
UF/heat/protease, with or without bentonite addition, was compared against traditionally
bentonite fined wine. Heating retentate (with and without protease) removed significant
quantities of haze-forming proteins, thereby improving the heat stability of recombined
wine. As a consequence of protein removal, the bentonite required to fully stabilise
recombined wine was also substantially lower. The results from volatile and sensory
analyses suggested that the combined UF/heat/protease treatments retained wine aroma and
flavour without imparting any oxidative characters to the wine, compared with bentonite
fining.
School/Discipline
School of Agriculture, Food and Wine
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2022
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