Filters – Ian Hickinbotham

By Ian Hickinbotham
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Ian Hickinbotham, author of Australian Plonky

Ian Hickinbotham, author of Australian Plonky

Australian Plonky by Ian Hickinbotham


Filtering of wine is a relatively recent winemaking process but its value is increasingly questioned.

It is a widespread belief among winemakers that filtering removes some good characteristics as well as the unwanted ones, the most common complaint being the removal of some of the desirable flavour. However this basic but important assertion seems to be based on logic only.

I do not know of any properly-designed tests having been conducted to prove that filtering removes some flavour from wines, yet it would seem to be quite easy to do simple duo-trio style tests. This entails providing three glasses of wine, two of which are the same: the filtered wine, for example. The third glass contains the same wine, but unfiltered. The examiner mixes the glasses around and participants are invited to find the wine that is different – they have to succeed at least four times out of five tries. An imponderable factor, however, is a common belief that wines recover after filtering – but slowly.

The extreme type of filter was loosely defined as ‘germ-proof’ filtering, which may have ‘defined’ the action, but horrifies modern oenologists. It really meant that all bacteria were removed from the wine, while inadvertently disclosing that bacteria were present in the wines to be treated.

Truth be told, oenologists have only been able to remove all the bacteria from wine in the past 30 plus years, meaning filters capable of removing them are a recent development, thanks to chemical engineers rather than winemakers. But wines so treated are usually those with some retained grape sugar (probably the most popular type).

When first made, the consistency of wine can be compared to ‘pea soup’, especially in the case of red wine as, unlike most white wine making, the fermentation proceeds with the juice and the grape skins together as the skins contain the required colour. The red grape skins are pressed and the ‘pressings’ are usually added to the liquid component derived by draining as much of the juice as possible from the crushed grapes without any application of pressure.

After futile use of reeds and similar natural plant material, early filters were simple compressed cotton particles: significantly this cotton could be washed and re-used many times. Then paper-based compressed pads were universally used, while their porosity was varied by the addition of asbestos. Perhaps fortunately, these ‘one-use pads’ did not need to be handled excessively by cellar hands.

The big advance has been the introduction of cross filtering. The wine does not ‘pass through’ the filter, but rather, is flows passed a membrane and suspended particles adhere. Importantly the process is the most gentle filtering type and so enjoys winemaker enthusiasm.

Objectively, winemakers would prefer not to filter their wines. Really they filter so wines can be presented as clear beverages, believing that is what the public want. The day may come when modern consumers accept bottled wines that need to be poured carefully so deposits remain as dregs in bottles.

Aside from the cost, there has been past unfortunate experience, however. Bottled white wines especially used to 'throw' a deposit when stored in refrigerators (that really only became installed in household kitchens after the war). Prolonged storage at around 5 degrees centigrade can cause the natural cream of tartar in the wines to precipitate as crystals, but many customers were quite alarmed, believing those crystals were pieces of glass. The remedy entailed expensively refrigerating the wines when still in the winery to cause precipitation of the cream of tartar crystals before bottling.

Though currently generally confined to the vineyard, perhaps with the increasing acceptance of biodynamic and organic practices, unfiltered wine will enjoy similar enthusiasm. Brave winemakers are the first need.


Ian Hickinbotham, one of the most innovative and influential oenologists in Australia over his 50 year career, is the author of Australian Plonky (see related review below).


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September 20th, 2010
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