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A Technical Guide for Wine Producers
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WHAT'S UP IN THE VINEYARD AND CELLAR
Cross flow filtration
The clarification of juice or wine is one of the standard production practices at all wine cellars. Different fining agents, filtration aids and mechanical clarification equipment such as filters and centrifuges are available and depending on the size of the cellar and the composition of the product portfolios, winemakers must be sensible when selecting the most effective practice for their circumstances.
Cross flow filtration has been used in the food industry since 1960, but only really took off in 1980. At the time the technology was developed for a different industry and it was not even adapted to the wine industry. The wine industry experienced various problems with cross flow filtration. Different quality problems ensued because of oxygen uptake and increases in temperature that occurred during the winemaking process and wines were practically stripped of their character. Moreover, the equipment was difficult to operate and very expensive to purchase. As a result, the technique was used for low quality white wines only and not highly regarded by the wine industry. By 2000 it had practically disappeared from the wine industry.
The manufacturers of the equipment then started paying attention to the development of technology for the wine industry and membrane technology in particular saw vast improvements. Since 2005 it has featured increasingly in wine industries. Operating the equipment is now much simpler and the capacities of the units have been adjusted for use in different size cellars. Actual aspects such as labour, wine losses, difficulties with diatomaceous earth and filtration quality were addressed. The “new” cross flow filtration techniques are now able to execute any type of filtration from solids and tartrate stabilisation to volatile acid removal and yeast or bacteria removal. It is practically possible for plate and frame filtration to filter more fluids per unit surface, but the ability decreases considerably when the filtration progresses and the filtration medium becomes blocked. On the other hand there is no possibility of blockage in cross flow filtration. Most of the cross flow filtration systems have a nominal pore size of 0.2 micron which implies that 95 to 98% of the particles will be removed from the liquid using this or a bigger diameter. A so-called absolute specification of 0.2 micron implies that 99% of the particles will be removed.
The NTU reading of wine refers to the degree of opacity. With cross flow filtration an opaque wine with an NTU reading of 1 000 may be clarified to 1. It is a continuous process and the effective throughput exceeds sheet filtration by far, especially when filtering large amounts of wine. There are considerable labour savings since only one person has to initiate and arrest the process. Neither sheet replacements nor rinsing of sheets takes place, consequently losses are restricted to a minimum. The potential health hazards associated with the use of diatomaceous earth as a filtration aid, obviously contribute to the popularity of cross flow filtration among wine cellars (Pregler, 2007).
A cost comparison between cross flow filtration and diatomaceous filtration, done in Europe, is indicated in Table 1 (Human, 2007).
Table 1: Cost comparison between cross flow filtration and diatomaceous earth filtration (R) (E1 = R10)
Reference
Human, G. 2007. Personal communication.
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