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Colloidal compounds like pectins and glucans which can't be detected via turbidity testing but can be by filterability testing. Filterability is therefore a better predictor of a wines ability to pass through bottling line membrane filters. 

In years where botrytis has affected fruit quality, it is important to recognise and be proactive about filtration issues.

Compounds, which are broadly classified as pectin, gum and polysaccharide, are extracted from grapes during the winemaking process. In healthy grapes these compounds will generally form colloids in the presence of alcohol during fermentation, and are removed during normal wine clarification operations.

When wine is botrytis-affected, the potential for blocking filtration membranes increases, even if the wine meets a turbidity specification of <1.0NTU. Polysaccharides, such as beta glucans derived from infected fruit, produce macromolecules which are soluble and, therefore, cannot be measured by turbidity testing. These macromolecules block filtration media.

El Rayess et al (2011) state that macromolecular compounds such as polysaccharides, phenolics and proteins are the major causes of membrane fouling. Given the variation in polysaccharide structures (viz. pectins, mannoproteins and glucans), this is of particular relevance to wine producers who do not use pectolytic enzymes, add mannoprotein to their wine, perform lees ageing or when Botrytis infection is evident, as these practices may contribute to higher levels of macromolecles and potentially higher fouling rates of filtration media. The difference between turbidity and filterability index measurements is explained below.

Turbidity

Turbidity is used as a means of assessing the particulate level in a wine (visual clarity).

Detectors measure the spread of a beam of light as it is scattered back towards the light source and the strength of the transmitted light. Light is scattered by particulate matter (suspended solids). A ratio measurement of the signals from all detectors provides a turbidity measurement.

This measurement helps winemakers to determine whether the settling, separation and filtration operations have successfully removed the suspended solids, and that there is little or no visible haze remaining.

This measurement has been used to provide a general estimation of the filtration performance of a wine through 0.45µm and 0.65µm membranes.

Filterability index

A filterability index involves using a pressurised device to force wine through a membrane under conditions of constant pressure and measuring its flow rate. This measurement technique provides a more direct indication of the filtration performance of a wine through 0.45 µm and 0.65 µm membranes.

 

Wines identified with a filterability index greater than 20 can be tested for the presence of polysaccharides.

If the wine is found to contain polysaccharides, it can be treated with enzymes and then filtered.

The enzyme preparation will hydrolyse both pectin and glucan-type macromolecules to improve wine filterability. This takes a minimum of two days to properly react with the glucan macromolecules and must be followed by bentonite fining to deactivate the enzyme and assist in the clarification of the wine.

Wines with poor filterability not related to glucan levels can be treated using filtration to allow them to be brought into bottling specification of <1.0NTU.

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Last modified on Friday, 29 January 2016 13:56

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