Winemakers will soon have a suite of options to produce protein and heat stable wines, delegates at the recent Australian Wine Industry Technical Conference heard.

‘While bentonite addition has been the most widely-used approach for many years, some winemakers have indicated they would prefer a commercially-viable alternative that can selectively remove proteins without changing the sensory profile or removing wine as lees’, said Dr Jacqui McRae, formerly with the Australian Wine Research Institute (AWRI) and now hub manager for the University of Adelaide’s ARC Graphene Research Hub.

She said the key message from the research she presented at the conference was that they would soon have greater choice – and be able to choose the best alternative for their particular wine.

The current alternatives

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Carrageenan comes from red seaweed and is an alternative to bentonite.

So, what are the alternatives, and when will they be available?

Dr McRae says the short-term alternatives are currently a three-way tie ‘with several options very close to being available for winemakers’.

Carrageenan

Carrageenan comes from red seaweed and is a renewable and natural product. Recent trials have shown that carrageenan is more selective than bentonite in removing wine proteins without also removing desirable wine sensory compounds.

Where it’s at: Currently available but waiting for approval in all export markets.

Pasteurisation

‘Flash pasteurisation’ may be a viable strategy for heat stabilising some wines with minimal lees production.

Where it’s at: No approvals are required, but additional equipment would be required to undertake the process.

Enzymes and pasteurisation

Heating grape juice in the presence of Aspergillopepsin (AGP) enzymes prior to ferment can produce heat-stable wine, making enzymes a viable alternative to bentonite.

Where it’s at: Approved in almost all markets and currently awaiting availability from suppliers.

Medium-term bentonite alternatives

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After grape seeds are roasted and crushed to a powder, they can be added to grape juice to bind haze-forming proteins.

Grape seed powder

Grape seeds contain high concentrations of polyphenols that readily bind to proteins. After seeds are roasted (180°C for 10 mins) and powdered, they can be added to grape juice to bind haze-forming proteins. The juice is then racked and fermented, producing clear, bright and protein stable wine.

‘This approach has demonstrated very promising results on a lab scale and warrants further research to assess the impact on wine sensory properties’, Dr McRae said.

Where it’s at: Readily available and inexpensive, but needs proof-of-concept on a large scale.

Membrane technology

The membrane process involves transferring protein-unstable wine through a membrane to give protein-stable, clear and bright wines. The challenge with the technology is ensuring other wine components are not extracted in the process and there is no protein ‘breakthrough’.

Where it’s at: A research project conducted through the University of Adelaide is liaising closely with VFA filtration to produce a commercially-viable solution.

Longer-term alternatives

Image: Agnieszka Mierczynska-Vasilev

Magnetic nanoparticles are placed in heat-unstable wine, where the proteins bind to the nanoparticles’ surfaces. The particles can then be removed using a magnet (image on right).

Dr McRae says the longer-term alternatives, still in early phases of proof-of-concept include:

Magnetic nanoparticles

Nanoparticles are coated to make them selective for wine proteins and are added to protein-unstable wine. After a short interaction time, the use of an external magnet attracts the protein-rich particles to bottom of the tank or to an inline trap, leaving protein stable wine and minimal lees.

‘This exceptionally promising technology has demonstrated efficacy at lab scale and further work will investigate the commercial feasibility at larger scale’, Dr McRae said.

Read more about magnetic nanoparticles here.

Zeolites

These work in a similar way to bentonite but settle more efficiently, reducing the amount of wine lost as lees compared with bentonite addition.

Dr McRae said while it there were some exciting options for winemakers in the future, she doubted bentonite would ever be completely phased out.

‘Bentonite has been around for a long time and many wineries, particularly larger wineries, have adapted their procedures to minimise any side effects.

‘The aim of this research is to give winemakers options for ensuring protein-stability without relying only on bentonite.’

Dr Jacqui McRae