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A Technical Guide for Wine Producers
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WHAT'S UP IN THE VINEYARD AND CELLAR
Brettanomyces test within 3 hours
There is little doubt about the fact that Brettanomyces occurs throughout the entire wine world and much research has been done regarding preventative actions to be implemented in cellars in order to limit the influence thereof on wine. Prevention is better than cure in all instances, but so far cellars have not been able to ascertain at an early stage to what extent Brettanomyces contamination is already present in wines. With this instant test the problem may be solved.
As a result of current cellar practices such as post-fermentation skin contact, barrel maturation and a reduction in the use of sulphur dioxide, favourable conditions are created for Brettanomyces and as a result thereof wine spoilage is increasingly prevalent. Once it occurs in a cellar, it is also difficult to get rid of it. Some strains of Brettanomyces grow like mould and are therefore able to penetrate the surface of wine barrels. Once alcoholic fermentation has run its course, high populations of the yeast may occur as it is highly resistant to alcohol.
It is usually identified in barrels with wine since it may form strong flavours such as plaster, sweatiness and wet dog. One of the compounds, 4 - ethyl guaiacol, may impart a pleasantly spicy flavour to wines, but it is usually dominated by 4 - ethyl phenol which results in the unacceptable flavours mentioned above. Brettanomyces is also involved in the formation of biogenic amines which cause headaches in wine consumers.
The monitoring of Brettanomyces remains a problem for most wine cellars, however. Although different methods are currently available to identify Brettanomyces, it takes one to two weeks and spoilage may occur before it is noticed by the winemaker. Fast methods are indeed available, but these are too expensive and require costly equipment, time and expertise. A simple, quick method that is able to confirm the presence of Brettanomyces within hours may help the winemaker to implement preventative actions in good time. Winemakers who desire a mild Brett character in their wines are also able to monitor the population.
Immuno-based tests for pathogen determination are replacing microbiological tests in the medical discipline. The availability of immuno chemistry to test spoilage yeasts and bacteria in wines has also not been exploited yet. The modern DNA sequencing technique can also be used to identify spoilage organisms such as Brettanomyces at an early stage. The so-called Miragene Zeta-Grip method requires hardly any special equipment, is inexpensive and the results may be obtained within 3 hours. Although the technique was initially developed for medical application, researchers at the University of California collaborated to develop a quick, inexpensive test for Brett.
The develoment of the test is still in its infancy, but it is expected to exist of a white test strip in a plastic cover which will be approximately the size of a small matchbox. It will be possible to apply different samples to identified numbers with an eyedropper. Samples may possibly be concentrated using centrifugation before being applied to the test strip. Once 10 samples have been applied to a test strip, it will be exposed to different solutions that are supplied as part of a solution set, shaken and a development reagent will then be added. The development reagent causes a purple discoloration in samples containing Brett. The intensity of the discoloration is equal to the population of Brettanomyces in the sample. In order to ascertain the actual concentration of Brettanomyces, the test strip is scanned and a computer programme may be used to quantify the population.
Preliminary tests have indicated that a Brettanomyces population of ca 1000 cells/ml may be observed using the test. The method has to be finetuned, however, seeing that reaction with other yeasts also occurs and an attempt is being made to observe Brettanomyces populations of as low as ca 10 cells/ml. It may be possible to use 0.45 micron membrane filters in conjunction with the method so that counts might be done on the filter matrix. The Zeta-Grip technology could possibly also be used for a simple and rapid count of other yeasts and bacteria in wine.
Reference:
Rodrigues, S.,Lebrun, S., Akaboshi, E., Edinger, W., Thornton, R. 2006. New, Rapid Test for Brett Shows Promise. Wine Business Monthly February 2006: 61-62.
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