In Processing

Nowadays, going green is all the rage. People are driving electric cars, industrial carbon dioxide emissions are scrutinised and even flatulent cows are not escaping the wrath of greenies. So what does this have to do with the wine industry?

I’ve recently learned that bentonite is a big culprit, leading to wine losses equivalent to that of New Zealand’s annual white wine production. This loss of 1-3% represents 120,000-360,000 tonnes of grapes. The related liberation of greenhouse gases for irrigation, harvesting, pressing and processing of this amount of grapes was estimated at 36,000-225,000 tonnes of carbon dioxide per year. Unfortunately for mother nature, bentonite fining is an effective and simple method for the removal of haze-forming proteins.

Apart from wine that is trapped and lost in bentonite lees (up to 3%, even with subsequent rotary drum vacuum filtration-RDV), a considerable reduction in varietal character is also inadvertently effected when bentonite fining is done. It is well known that aroma and flavour molecules in wine can be adsorbed by bentonite, which in turn leads to an unwanted decline in wine quality. Further oxidation during recovery from the bentonite lees merely adds to the aforementioned decline.

Before you go on a witch-hunt and banish bentonite from your cellar, there is good news. It was found that in-line dosing in conjunction with RDV can significantly decrease wine losses. A short description of in-line dosing: Untreated wine is pumped from a storage tank to an injection point, where bentonite slurry (supplied from a slurry tank) is continuously injected into wine or juice. A static mixer disperses the slurry, ensuring even contact between wine and bentonite. A contact period of five minutes in pipe work is allowed before centrifugation is used to separate wine and bentonite. The problem with in-line dosing is that it is not yet widely used and installation can be costly.

Batch fining combined with RDV remains the most popular method in countries such as France, Italy, Spain, California (ostensibly a country), Australia, Germany, South Africa and New Zealand. Collectively, their white wine production represent 40% of all wine produced globally. The amount of bentonite required for protein stability varies according to a number of factors, such as year, fruit type and growing region. The report that I studied in Grapegrower and Winemaker Magazine (in preparation for writing this blog) indicated that with all factors taken into account, a dose of one gram of bentonite per litre of white wine will be assumed.

Let’s have a look at some more numbers relating to the use of bentonite in the above mentioned countries. They produced 80% of all white wine in 2008/2009 and revenue loss was more than US$820 000 per year. If the value of domestically sold wine is added to the export values of white wine, the aforementioned figure climbs to a staggering US$1 billion!

The scourge of pollution is slowly suffocating earth and with an estimated 80-250 million kWh energy requirement annually, we can’t afford not to research alternatives to bentonite fining. Keep watching this space!

Bernard Mocke is a technical consultant for Oenobrands

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