Novel fining agents to heat stabilise wine

Abstract

Bentonite, a type of aluminium clay is a low cost fining agent currently used to remove heat unstable and haze forming proteins from white wines though there are negative aspects to its use, such as quality loss and sustainability challenges. This study began with a screening process to identify the most effective types of polysaccharides to heat stabilise wine. The study also outlined the use of renewable polysaccharides (carrageenans) as an alternative to bentonite for heat stabilising white wine.

Summary

Kappa- and kappa- (90%)/iota- (10%) carrageenans were the most effective polysaccharides for heat stabilising white wine.

A range of commercially available polysaccharides was systematically screened in a 2014 Riverland Chardonnay wine for their ability to heat stabilise wine. A total of 28 carrageenans, 14 pectins, and three carboxymethylcelluloses (CMCs) were tested. None of the pectin polysaccharides tested could heat stabilise wine to less than 2 NTU. The CMC polysaccharides did not improve heat stability. Only two types of carrageenan polysaccharides, the kappa- and kappa- (90%)/iota- (10%) type carrageenans , were found to consistently heat stabilise white wines. Pure iota- and pure lambda- carrageenan types did not effectively heat stabilise wine and may cause filtration difficulties.

A mechanism has been proposed for heat stabilisation of juice/wine with carrageenans. It is likely to involve the formation of an electrostatic complex between the negatively charged sulfate groups in the kappa- carrageenan and positively charged wine proteins that entrap and precipitate the wine haze proteins through sedimentation. The project has also outlined and tested methods for characterising carrageenans analytically, so that quality control parameters can be defined and checked to ensure winemakers are using the most optimal fining agent.

Polysaccharide analysis allowed the definition of quality control parameters for identifying the most effective carrageenans to use, as well as defining several critical parameters to ensure product integrity. A 1H-NMR technique has enabled the identification of different types of carrageenans — e.g. kappa-, iota-, or lambda-, that are present in a carrageenan sample. Polysaccharide linkage analysis can be used to determine the molar % of kappa-, iota- and lambda- carrageenan in one sample.

Carrageenans can be added at different stages of the winemaking process to heat stabilise wine. In pilot-scale winemaking trials, the carrageenans were added either at the juice stage, at the fermentation stage, or to finished wine, and ultimately resulted in a heat stable product. As such, carrageenans can be added with the intention of being removed as part of the lees separation process, such as during flotation, racking or centrifugation. This may provide the benefit of streamlining the winemaking process and reducing the number of tank movements required to produce a finished wine.

Adding carrageenans to juice or wine required vigorous tank mixing and a relatively large volume of carrageenan/juice/wine stock solutions. The carrageenans were added in slightly lower quantities than bentonite, but were still able to heat stabilise the same wine.

Carrageenans need to be added in conjunction with pectolytic enzyme treatment, when added at either the juice or fermentation stage, to avoid filtration difficulties. The carrageenan fined wines made from enzyme treated juice were found to be compatible with cross-flow filtration.
Wine quality was acceptable for wines fined with carrageenan. Descriptive sensory analysis indicated that wines fined with carrageenan had more tropical fruit characters than wines fined with bentonite.
No taints were observed in any wines fined with carrageenan. In descriptive sensory analysis, the bentonite wines showed lower intensity of most sensory attributes, and were described as ‘stripped’ compared to the untreated control; several of the carrageenan treatments wines had higher intensity of tropical fruit-related attributes (box hedge, sweaty, passionfruit) and also higher viscosity.

The cold soluble (sodium salt) type kappa-carrageenan increased sodium levels in the wine to three times the levels found in the control wine, which had no fining agent added. Calcium levels, after using pure (potassium salt) carrageenans, were slightly modified. Quantities of potassium, copper, iron, magnesium, and manganese did not appear to be impacted by the carrageenan fining agents to any level that would cause a metal instability or impact current export limits.

At time of publication the use of carrageenans to heat stabilise wines is substantially less cost effective than using bentonite.
Currently, bentonite costs approximately $1.50 - $2 per kilogram, whereas carrageenans can range in price from $27 - $48 per kilogram. Adding carrageenan at winemaking stages that generate wine solids (lees) — e.g. during juice clarification or fermentation, or prior to cold stabilisation — facilitates the removal of the carrageenan along with the juice or wine lees. We do not currently have conclusive wine recovery data (such as % gross lees) to indicate that the use of carrageenans in wine decreases the proportion of lees.

At the time of publication, carrageenans are not permitted additives in wine. At present, pectin and carrageenan are not permitted additives in wine, although they are approved for food use. An outcome of this research is that the Winemakers’ Federation of Australia (WFA) has submitted an application to Food Standards Australia New Zealand (FSANZ) seeking to amend Food Standards Code – Standard 4.5.1 to approve the use of pectin/carrageenan in commercial Australian winemaking.