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A Technical Guide for Wine Producers
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RECENT ARTICLES | WYNBOER HOME
WINE IN WOOD AND WOOD IN WINE
The use of high-power ultrasonics to clean and sanitise barrels
The porosity of oak barrels plays an important role in the wood maturation of wines. Without it barrels would simply impart an oak character to the matured wines without enabling the interaction between oxygen and oak components during maturation. The porosity of wood also enables the wine to penetrate the barrels to ensure a more effective utilisation of the wood. This movement of wine also causes micro-organisms to settle in the wood and consequently the cleaning and sanitation of barrels is crucial.
Barrels have been used in the vinification process for many centuries and they come in different sizes. It is estimated that approximately 7 million barrels are currently being used in wine cellars around the world. The financial impact on the production cost of wine is enormous and it is therefore important for barrels to be used as effectively as possible. In this regard winemakers are concerned about evaporation losses that occur during maturation as well as the possible microbiological contamination of barrels. Throughout the world the increasing occurrence of Brettanomyces/Dekkera is a major concern. Its dispersion in wine cellars may be ascribed to the use of contaminated equipment such as hoses, pumps and barrels. Much research has been done on the timeous identification of the occurrence of Brettanomyces/Dekkera, but information on techniques to limit its distribution is scant.
During the maturation of wine in barrels or the use of alternative wood products, cream of tartar (K-bitartrate) is precipitated on the surface and colourants, proteins, lees and other micro-organisms settle in the containers. However, some of these components are also able to penetrate the pores of the wood, and microbic biofilms might even be formed on the surface of the wood. Due to the formation of biofilms, increased resistance to solubles and antibiotics is created. The effectiveness of sanitation procedures depends largely on the extent to which they succeed in dissolving biofilms. Acetic acid bacteria, lactic acid bacteria and yeasts are adapted to growing in a vinous environment and the growth of mould may also occur inside barrels if sufficient drying and treatment with sulphur dioxide do not take place aften cleaning. Barrels infected with acetic acid bacteria or moulds are usually not suitable for repeated use, as it is extremely difficult to remove the flavours that are thus formed.
Current methods and practices to clean or sanitise barrels may be summarised as follows:
Low or high pressure cold and warm water: A variety of manual or mechanised equipment for barrel washing is currently available. Warm water at 60 to 82 degrees C is used in combination with pressure ranging from 680 to 2684 kPa. This is usually followed by a cold water rinsing process. At the above-mentioned temperatures the soft tartrates will be dissolved, but temperatures above 85 degrees C or steam are usually required to remove the hard tartrate deposits from barrels. Moreover, the above-mentioned temperatures will ensure limited surface disinfection only. Steam is required to disinfect the internal surface of barrels, but only to a depth of 2 millimetres, while wine penetration occurs to a depth of 8 millimetres.
Chemicals: Various products, including solutions of caustic soda( NaOH ) or potassium carbonate may be used to dissolve the tartrates. Such treatment is usually followed by citric acid and water rinsing processes. If barrels are not reused directly after cleaning, they should be filled with sulphur dioxide gas and the bung hole sealed to prevent the growth of mould. Although ozone is occasionally used for barrel sanitation, no scientific proof regarding its effectiveness currently exists.
Shaving of barrels: Barrels may be shaved from 1 to 3 millimetres to remove the tartrate deposits on the inside. At that depth all micro-organisms will not be removed, however. Toasting of the shaved barrels might well destroy all micro-organisms, but on the other hand such treatment might also create undesirable flavour components in the wood. The shaving of barrels will nevertheless remove toasting blisters that occasionally occur in barrels, serving as growth medium for micro-organisms.
Dry ice particle radiation: The process entails the supersonic bombardment of the internal barrel surface with small dry ice particles which remove the wine residue and tartrates from the surface. ( www.barrelblasting.com ) This being a surface treatment only, micro-organisms in the pores are not removed or destroyed.
Mikrowave treatment: The treatment involves the use of a combination of high pressure warm water, alkaline cleaning agents, acid solutions and microwave treatment for cleaning and disinfecting barrels. It is a time-consuming process that requires considerable infrastructure.
The influence of high power ultrasonics on food processing was recently investigated. The power thus created may be used to cleanse surfaces as well as porous internal structures. This process is able to destroy micro-organisms, change particle sizes of fluids and prevent the adhesion of undesirable matter to surfaces. Application possibilities of this technique to the cleaning and disinfection of wooden barrels or alternative wood products may be summarised as follows:
For more information about the new technique contact Andrew Tap at ayap@cavitus.com.
Reference:
Yap, A., Jiranek,V., Grbin, P., Barnes, M. & D. Bates. 2007. Studies on the application of high-power ultrasonics for barrel and plank cleaning and disinfection. Wine Industry Journal 22(3): 96-104
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