Introduction
Wine to be exported from Australia must be approved by a tasting panel of the Australian Wine and Brandy Corporation (AWBC). A recent article (1) by Steve Guy, Compliance Manager for the AWBC, outlined the main reasons why wines have been rejected this year. In this article we look at what these reasons are and how to reduce the risk that your wine is rejected for these faults.
AWBC Procedure
All wines intended for export from Australia must have 2 bottles sent to the AWBC for tasting by a volunteer tasting panel (see their website for details www.awbc.com.au). The wines must also be tested for a number of parameters in laboratories such as Vintessential prior to the tasting.
These tasting panels are held every week day at the AWBC Compliance Centre in Adelaide. The panel of 2 judges tastes up to 70 wines each session. If the panel members decide that a wine is not fit for export then the producer has the choice of either resubmitting samples to a second panel, or not exporting the wine. Sending the wine to a second panel costs more in both money and time. For an export consignment about to be shipped, the non approval of one wine can lead to serious inconvenience.
Faults that cause wines to be rejected
Below is a list of the reasons why wines were rejected in the February to May period of 2008 by the AWBC panels:
1. Oxidation 36%
2. Excessive sulfides 26%
3. Excessive volatile acidity 17%
4. Other (mousiness, hazes taints, Brett character) 21%
Of the 5500 wines submitted between February and May 2008, 167 or 3% were rejected. Surprisingly, the majority of these faults are relatively easy to rectify prior to submission.
As well as a waste of time and money for producers, rejection can lead to lost export orders. When winemakers are looking at all areas of their business to save costs it is sensible to try to ensure their wines are not rejected by the AWBC.
Managing faults and reducing the failure rate.
Although the list of faults above is not exhaustive, it is a good starting point as it gives hard data on the main faults to concentrate on. These faults will be considered in descending order of occurrence at the AWBC:
1. Oxidation
As the article by the AWBC states “…many of the wines rejected for displaying evidence of oxidation represent wines proposed for export in bulk”. This means that the samples were taken manually from a tank and were not bottled on a bottling line. It may not, therefore, be the case of an underlying fault with the wine; it could be a problem of sampling.
Some guidelines on how to improve this sampling were mentioned in the AWBC newsletter. Basically it is a matter of hygiene with sampling equipment.
Some steps to be followed include:
-ensuring wine has correct pH and sulfur dioxide levels
-circulating the wine in tank to ensure homogeneity prior to sampling
-cleaning sampling equipment
-dosing bottles and sample collection devices with inert gas
-bottling the wine as quickly as possible once collected
2. Excessive sulfides
This has certainly become more of an issue with the widespread use of screwcaps over the past few years in Australia. More careful copper fining trials need to be performed for wines bottled under screwcap, compared to natural cork. This has been well studied and discussed in the past few years.
The copper fining trials must be done on all wines and a dosage used that ensures there is no trace of sulfides discernable. The use of a panel of tasters in the winery would make good sense as well, rather than just relying upon one palate.
Of course the main formation of sulfides is caused by poor nutrition of yeast during the primary fermentation. Measuring the Yeast Assimmilable Nitrogen (YAN) content of juice and following sound nutrition management with well formulated yeast nutrients is a proactive step to take to stop the formation of sulfides. It is obviously much better to try to produce little or no sulfides at fermentation, than forming the sulfides and then trying to remove them later with copper treatment.
Another related issue to consider is the amount of residual copper in wine. In Australia the maximum copper content allowed in wine is 5 mg/L (ppm). Although this is not a test required by the AWBC for export approval, it is one that a lot of our customers have done to ensure they are not over the limit and also to check the potential for the haze caused by copper casse.
3. Excessive volatile acidity
The test for Volatile Acidity (VA) is one that has to be performed for the AWBC Certificate of Analysis. The Australian limit is 1.5 g/L. If the Certificate of Analysis has the VA at less than 1.5 g/L then the wine cannot be refused approval for Excessive VA.
Producing wines with acceptable VA levels requires good management practices, particularly in regard to pH and sulfur dioxide levels. Barrel aged wines require good cellar management to ensure VA does not become an issue. If excessive VA does occur it can be removed nowadays by contract Reverse Osmosis operators.
Related to this issue is the common misconception in the Australian wine industry that VA also measures the Ethyl Acetate content of wine. It does not. Ethyl acetate has nothing to do with VA. VA is a measure of acidity, but Ethyl Acetate is not an acid!
Unfortunately many people in the wine industry still refer to the aroma of Ethyl Acetate as “volatility”. This is a very poor expression to use as it causes much confusion. A better description of the characteristic caused by Ethyl Acetate is Ester Taint. I first heard this expression used by Dr Paul Grbin from Adelaide University at a conference several years ago. If we all used this descriptor it would save a lot of confusion on this issue.
So, some wine judges may decide that a wine has excessive Ethyl Acetate. That’s fine, let’s just make sure they are using the much better description of Ester Taint. If they use the expression Volatile Acidity, and you know your VA is below 1.5 g/L, please set them straight!
Ethyl acetate can be measured by Gas Chromatography and is done so in our lab for a number of clients to ensure it is not excessive. Typical descriptors used for Ethyl Acetate are “nail polish” or “varnish”. These are quite different to the aroma of VA which is typically “vinegar”.
4. Other faults
Other faults mentioned were:
-mousiness
-hazes
-taints
-excessive Brettanomyces character
The interesting aspect of this list is that all these faults combined only gave rise to 21% of the wines that were rejected.
The big bogey man of the industry for the past 10 years, Brettanomyces, did not cause as many rejections as Oxidation or Excessive sulfides. If may well even be less than those wines rejected for Excessive VA (Brett was not listed separately so it is not clear exactly how many wines were rejected for Brett).
It appears that many winemakers now have a much better management system in place for Brett. This is great news. The bad news appears to be that 3% of winemakers are still grappling with managing basic faults such as Oxidation, Sulfides and VA.
Conclusion
The data from the AWBC Compliance Centre can be used as a guide to where you should focus your winemaking efforts. It appears more effort needs to be made to focus on eliminating:
-Oxidation
-Sulfides
-Volatile Acidity faults
Eliminating faults such as these should be relatively simple. Doing so should save you time, money and effort in the process of having wines approved for export.
References
1. S. Guy, “Sampling bulk wines” Wine Australia Magazine, July – September 2008, issue 14, p6
