Oenology

Precoat filtration using cellulose fibers

Filtration-capable diatomaceous earth is both a health hazard and disposal problem. As an alternative, the WZG Möglingen (wine co-operative) began trials using pure cellulose fibers in the precoat filtration.

The precoat filtration is, to this day, a tried and tested method to clarify young wine effectively and economically. In the wine branch, practically the only filter aid used for this is diatomaceous earth. The filtration-capable diatomaceous earth is usually calcined or flux calcined diatomaceous earth. Calcination is a high temperature procedure where respirable cristobalite is created in amounts of up to 60%. If this is inhaled, silicosis may result. The silica can lead to work-related cancer which is why cristobalite has been classified as a carcinogenic substance by WHO.

Disposal

In addition, the disposal of the used diatomaceous earth is becoming more and more problematic. In many places transport to waste disposal sites is not possible due to the high water content and the percentage of organic portions. Currently disposal in compost operations is still possible. A classification as hazardous waste is not far away.
The problems mentioned have caused the WZG (wine co-op) to look for alternatives to diatomaceous earth. Motivated by the company Rettenmaier, trials using pure cellulose fibers in precoat filtration were carried out in February 2003.
Cellulose is classified from a chemical standpoint as a polysaccharide made up of glucose molecules. A renewable raw material, cellulose has ecological advantages over diatomaceous earth.
The fibers are soft and do not react abrasively towards the machinery. The disposal of the used fibers is trouble-free over composting, animal feed, incineration or even as raw material. The biggest advantage in comparison to diatomaceous earth is however, that there it is not a health hazard for the user.
The first attempts were extremely successful and showed that a wine filtration with pure cellulose fibers is possible. And there have been extremely promising results in numerous other trials where the use of cellulose was tested and optimized.
In the first clarifying filtration, a significantly reduced loss of color was analyzed when compared with diatomaceous earth.

At the beginning of our test, the first clarifying filtration, the degree of clarity when using cellulose did not correspond to the degree obtained in the filtration with coarse diatomaceous earth.

In the first clarifying filtration, a significantly reduced color loss could be analyzed when compared with diatomaceous earth.

Filtration properties

At the WGZ two filtration methods are used customarily before the wine is stored in the end sterile filtration. With the first filtration after fining and separator, coarse diatomaceous earth is used, with the second following the blending of the wines, a medium and fine diatomaceous earth is used.

Degree of clarity

At the beginning of our trials, in the first clarifying filtration using cellulose, the degree of clarity (measured in NTU) did not correspond to the clarity obtained with coarse diatomaceous earth (see Diagram 1). This can negatively affect the following filtration steps.
A longer fiber cellulose product was used here to stabilize the cake and a medium-sized fiber product was used for the filtration. By using finer fiber types, the degree of clarity could be optimized. For the first clarifying filtration, short to medium-long fibers should be used and for the second filtration before the sterile storage, a powdery cellulose product is used. The range requirements needed in the first filtration can be met using conventional products from the Rettenmaier company. For the second filtration, a test product with an extra fine milling grade was provided.
The quantities of filter aid required in the tests done were: diatomaceous earth: 1.3 - 2 g/l wine and cellulose 0.5 - 0.8 g/l wine.
In the first clarifying filtration, a significantly reduced color loss was seen with cellulose as compared with diatomaceous earth (s. Diagram 2).
The handling of cellulose is trouble-free. By using a longer, more cubic cellulose type, which was added during the precoating, the filter cake can be stabilized and the cleaning up can be greatly improved.

Tasting by the cellarers' advisory council at LVWO Weinsberg( Teaching and testing facility for wine and fruit agriculture) on 21st May 2003 in Weinsberg. Preparation and evaluaton Dr. Schmidt and staff.

Tab.1: Wine tasting Lemberger on 7th April 2003

Batch	place 1	place 2	place number	ranking number
precoat filtration with diatomaceous earth	1	6	1.86	2.27
precoat filtration with cellulose	6	1	1.14	1.28

A Wurttemberg Lemberger wine which was filtered in the first filtration with diatomaceous earth and alternatively with cellulose, was judged significantly better by several of the wine tasting trials with experts.


Sensory properties

At the beginning of the series of trials, the use of cellulose directly after the precoat filtration resulted in a distinct paper aftertaste. After only a short time, however, this aftertaste was no longer detectable. Thereafter another cellulose product was used from a different raw material group which is more neutral and is mainly used I the pharmaceutical industry for filtration purposes.
A Wurttemberg Lemberger wine which was filtered in the first filtration with diatomaceous earth and alternatively with cellulose, was judged significantly better by several of the wine tasting trials with experts. (see Table 1 and Diagram 3).
The sensory advantage is probably due to the fact that cellulose has a much lower absorption capacity than diatomaceous earth. The reduced loss of color is apparently also due to this property.

Costs

The additional costs of the raw material when using cellulose are 100% - 150% higher when compared with diatomaceous earth. These additional costs are compensated due to the significantly lower filter aid consumption.
Additionally there is also less residue which must be disposed of. If there is a change in the future regarding the disposal regulations for diatomaceous earth, cellulose will even have a cost advantage.

Conclusion

Through the use of cellulose fibers in the precoat filtration, an attractive alternative to diatomaceous earth was discovered. The lower consumption rates offset the additional costs of the raw materials. Sensorially, a wine filtered with cellulose was rated significantly better than one filtered with diatomaceous earth. The most positive property of this filter aid is, however, the health aspect and the fact that it is harmless to the user.
The WZG will be optimizing the use of cellulose further. A filtration of unfermented grape juice during the fall campaign 2003 and the clarification of young wine for the year 2003 are planned.

More info?
If you have questions about this article, the "Der Deutsche Weinbau" authors, Wilfried Dörr and Ute Bader, WZG Möglingen. Telephone: **49 (0) 7141 / 48 66 23, will be happy to hear from you.


Source: Der Deutsche Weinbau (German Viticulture), 12th September 2003, No.18