Winetech Technical Yearbook 2022

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the unstable proteins and the resulting stable wine blended back into the protein-stable permeate. The advantage of this strategy is that a smaller volume of the wine will be subjected to potentially quality influencing stabilisation processes such as bentonite fining or pasteurisation. Recently researchers investigated this stabilisation strategy 1 using a Sauvignon blanc wine as this varietal is known for its high protein content. The retentate of a filtered wine was subjected to various stabilisation processes and blended back into the permeate. The main findings of this study will be reported here. MATERIALS AND METHODS A Sauvignon blanc wine was filtered using ultrafiltration. The commercial crossflow membrane filtration system was equipped with a 5 kDa spiral-wound polyethersulphone membrane. Fifty litres of wine were filtered to deliver 40 L permeate and 10 L retentate. The retentate was divided into aliquots, and stabilisation treatments were subsequently carried out on each aliquot to reduce their protein concentrations prior to recombination with the permeate in a volume ratio of 1:4 (retentate:permeate). The stability of the recombined wine was tested and compared to an unfiltered sample that was not subjected to any stabilisation processes (UNF-UN) and an unfiltered sample that was stabilised using bentonite (UNF-B). Tests were done in triplicate. Table 1 shows the treatments tested in the study. Heat treatment was done at 62°C for 10 minutes. DSM (Royal DSM, Heerlen, Netherlands) protease was added at the 0.05% v/v dosage as recommended by the manufacturer. Additions were made immediately before heating. Bentonite additions were unique for each treatment, and the specific requirements were calculated based on the results from the heat stability tests. During heat stability tests, samples were considered to be heat stable when the change in turbidity (ΔNTU) before and after heating and cooling (two hours at 80°C then three hours at 20°C) was <2 NTU as measured using a turbidimeter. RESULTS AND DISCUSSION Protein removal, heat stability and bentonite requirements Protein concentrations in the treated retentate samples were significantly lower than in untreated. Heating removed 39% of haze-forming proteins in the retentate, while the addition of protease during heating removed a further 15% of haze forming proteins (54% overall). The three bentonite-treated

INTRODUCTION Clarification and stabilisation of wines are essential to prevent turbidity and precipitation issues after bottling. Bentonite fining is commonly used by the wine industry as a clarifying agent and is a popular choice due to its low cost, high efficiency and easy handling properties. However, its use has certain disadvantages. It causes considerable product losses (up to 10% of total wine volume) because of the high percentage of lees formed. The resulting lees also contribute to cellars’ solid waste, which can have a negative environmental impact. The stripping of aroma/flavour and colour from wine when excessive amounts of bentonite are used has also been reported. Alternative stabilisation methods have been explored. Potential alternatives include carrageenan, grape seed powder, magnetic nanoparticles and zeolites. Processes such as pasteurisation, enzyme-pasteurisation combination, and membrane technology have also succeeded. The membrane filtration process is a physical separation method characterised by the ability to separate molecules of different sizes and characteristics. Its driving force is the difference in pressure between the two sides of a special membrane. The transfer of a protein-unstable wine through a suitable membrane will deliver a permeate (part of the wine that moved through the membrane) of which the unstable proteins have been removed, while the retentate (part of the wine that did not move through the membrane) will contain the unstable proteins. The retentate will concentrate the unstable proteins in a smaller volume of wine. To prevent product losses, the retentate (containing the unstable proteins) can be treated using stabilisation processes to remove

TABLE 1. Description of the treatments applied.

Treatment

Code

1 Unfiltered wine

Untreated wine

UNF-UN

2 Unfiltered wine

Bentonite-fined wine

UNF-B

3 Filtered and recombined wine

Retentate untreated

F-UN

4 Filtered and recombined wine

Retentate bentonite fined

F-B

5 Filtered and recombined wine

Retentate heat treated and bentonite fined

F-HB

6 Filtered and recombined wine

Retentate heat treated and protease treated

F-HP

7 Filtered and recombined wine

Retentate heat treated, protease treated and bentonite fined

F-HPB

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WINETECH TECHNICAL YEARBOOK 2022