Bentonite is most probably one of the additives used most generally during winemaking. It can be used together with other fining agents for the clarification of juice or wine, but is mainly used for the protein stabilisation of white wine. Its use has however certain disadvantages. It causes considerable product losses as a result of the high percentage lees and the resulting lees also contribute considerably to the solid waste of cellars.
Bentonite can physically be used in powder or granular form and chemically as Na or Ca form. The different forms have different properties regarding lees percentages and the efficiency of protein stabilisation. Winemakers do however agree that an alternative without the present disadvantages of bentonite will be beneficial. The potential alternatives can be divided between present, medium term and long term alternatives.
The present potential alternatives include carrageenan, pasteurisation and an enzyme-pasteurisation combination. Carrageenan is made from red seaweed and is a renewable and natural product. Recent research indicated that it is more selective than bentonite to remove proteins without removing other desirable wine constituents. It is already available, but the approval in wine markets is still outstanding. Flash pasteurisation can be an acceptable alternative for certain wines, without experiencing wine losses. No approval is required for it, but special, expensive equipment is required and its energy consumption is also high. The heating of grape juice in the presence of Aspergillopepsin enzymes can deliver a heat stable wine, which make enzymes a viable alternative for bentonite.
Medium term alternatives include grape seed powder and membrane technology. Grape seeds contain high concentrations of polyphenols, which can bind proteins. After grape seeds have been toasted for 10 minutes at 180°C it can be added to grape juice to bind the turbidity forming proteins. The juice is then racked and fermented, which will lead to a protein stable wine. Initial experiments were promising, but more information needs to be obtained regarding the influence it will have on the sensory characteristics of the wine. Membrane technology comprises the transfer of a protein unstable wine on one side of the membrane to its other side, where the wine will be protein stable. The retentate on the receiving side of the membrane will most probably contain the proteins and the wine permeate, which will move through the membrane and will be protein stable. The challenge of this process comprises the assurance that other wine components will not also be removed by the membrane and the protein removal is effective.
Longer term alternatives are still in an earlier stage and include magnetic nano particles and zeolites. Nano particles are covered to make it selective for wine proteins, before it is added to unstable wine. After a short interaction an external magnet is used to remove the nano particles with the proteins to the tank bottom. A stable wine with limited lees is obtained. It has however only been investigated on laboratory scale and its commercial feasibility must still be investigated. Zeolites are a group of micro porous size minerals consisting of hydrated alumino silicates of sodium, potassium and barium. It can readily be dehydrated and hydrated. It is used for cation exchangers or molecular separation, which function in the same way as bentonite, but settle more effectively, which result in less lees than with bentonite.
In spite of the potential alternatives for bentonite it will most probably not phase out completely because many cellars adjusted their practices already to address the negative results of bentonite (Anonymous, 2019).
Bentonite is a popular fining agent.
Reference
Anonymous, 2019. Is it a good night for bentonite? Australian and New Zealand Grapegrower and Winemaker, December 2019: 46.
