Quality Control in Cork Production
Kadia Austin
12/15/08
ESE 405/505
When a consumer buys an expensive bottle of wine the consumer expects the wine to have a genuine authentic taste and a pleasing aroma. What happens when the consumer instead finds the bottle of wine to have an odd taste and a musty odor? Chances are the bottle of wine has been “corked” or “tainted”. Cork tainting is a when a bottle of wine has an undesirable taste and smell even to the point that though harmless, becomes undrinkable. The main cause of cork tainting is the presence of TCA in the wine. TCA 2,4,6-Trichloroanisole is created when a naturally occurring fungi mixes with Chlorophenols which is an industrial pollutant found in pesticides and wood preservatives thus found in cork trees[1]. There are other factors that can cause a taint in the wine. These factors could be storage conditions, transportation methods of the corks and wine but it has been found that seventy to eighty percent of wines that are rejected by trained analysts is because of the TCA level of the wine [2]. Cork tainting has been a major issue in the wine industry because it can significantly reduce the quality and price of the wine. According to the Cork Quality Council, who is responsible for setting standards for cork production, the TCA level in cork shipments to the U.S. decreased by sixty two percent in the last two years[3]. This decrease can be attributed to the increase in the quality control, testing methods and standards in cork production.
Quality control and improvement involves activities that are aimed at ensuring that a product meet requirements and are continuously improved upon. On focusing of continuous improvement, the Natural Quality Cork Council sponsored a project done by ETS Laboratories. The purpose of this project was to develop a reliable process for detecting TCA in cork lots. They wanted to move from a sensory analysis which was less sensitive to TCA levels to a chemical analysis which would be much more sensitive to TCA levels. They wanted the analysis to be reliable and feasible for cork manufacturers.
The researchers began by adopting a process. The chemical process that they adopted was based on a combination of solid phasemicro-extraction (SPME) , gas chromatography, mass spec analysis (GC/MS) and Single Ion Monitoring (SIM). SPME is a fast and simple extraction process and GC/MS is another process used to identify different substances within a sample while SIM is used to accurately measure the sample which allowed for sensitivity to a level of 1.0 ng/L (ppt)[4] . Samples would be drawn directly from cork soaks which is a process where the samples would literally be soaked in wine. Samples would be calibrated by the use of deuterated internal standard. The human sensory testing can only measure TCA levels above 6ppt but the chemical testing would be able measure TCA levels below 6ppt. The system of testing the TCA level would be an automated process in comparison to sensory testing.
The researchers then wanted to investigate how cork soaks would work. One hundred corks were selected from four bales that had previously been rejected by cork manufactures. The samples were placed in 4L glass containers and soaked in 1.5L of dry white wine which contained 10% alcohol. They performed the analysis over various scheduled periods so that the most effective soaking time for detecting TCA level will be determined. Their results showed that the most effective time was a 24 hour soak time. At this time the TCA detection in the soak had reached equilibrium. This is displayed in Figure 1. Each line represents the TCA levels detected at a particular time from each bale.
Figure 1 TCA Detected in 100 Cork Soaks from Four Bales[5]
Past testing procedures done by the researchers involving TCA and corks was based on grinding up the cork and measuring the total TCA. Since the current testing procedure is based on cork soaks and measures only the TCA extracted, they decided to look at the correlation between TCA levels of the grinded cork and TCA levels from soaking the cork. Since testing the TCA levels by grinding the cork gives a better indication of the actual TCA level they wanted to see how much of the total TCA in the cork was actually detected by the soak process. Results showed that there was a poor correlation between total TCA and the amount of TCA extracted during the soak process. The results also showed that a very small percentage of the total TCA was extracted during the soak. Extraction values ranged from 0.05% to 2.0% of total TCA in the cork. This can be seen from Figure 2.
Figure 2 Total TCA vs. Soak TCA [6]
The researchers also wanted to see if the TCA levels will increase with repeated soaks. Two individual corks were soaked seven times for a period of 24 hours. They found that the TCA level remained constant. This phenomenon indicated that 24 hour soaks are bounded by the characteristics of the cork and is indicative of the amount of TCA that can be found in the actual wine. This can be seen in Figure 3.
Figure 3 TCA levels with repeated soaks [7]
The researchers wanted to determine if the amount of wine used in the soaking affected the amount of TCA that is detected. To test this, individual corks were soaked in 10ml and 50ml of wine. It was found that there was not much difference in the TCA level that was detected. This is displayed in Figure 4.
Figure 4 TCA detection vs Soak Volume
The researchers were now able to confidently characterize TCA levels with term and as a quantity. Releasable TCA is the term used to describe the equilibrium level of TCA in a given soak. They also determined that this quantity is a function of the TCA level in the wine, the alcohol composition of the wine and the composition of the cork. They found that detection of TCA was detected at higher levels in wines with greater than 10% alcohol contents. This was due to the fact that sensory analysis is more difficult at higher alcohol contents because the alcohol helps to masks the TCA characteristics.
Composite soaks of 100 random corks were examined to determine if the releasable TCA measured by the group was representative of the total population. The soaks were conducted for 24 hours in a wine solution containing10% ethanol. The composite soak solution was analyzed for releasable TCA and results were compared to the average releasable TCA measured by individual cork soaks taken from a second sample of 100 random corks from the same Bale. Fourteen Bales were tested. Results indicated a good correlation between the value from the composite soak and the average of individual corks. To determine reliability, the same process was applied to a different set of 100 random corks. This was repeated twelve times and the results were all consistent.
One hundred samples were taken from each of fourteen bales and the releasable TCA was determined. Figure 5 shows the results of four of the bales. It was found that the bales that had the highest concentration of TCA had very few corks with low TCA and bales that had a low TCA had very few corks that had a high TCA. This indicates that composite soaks can help determine if a majority of the corks in a bale have a low or high TCA concentration.
Figure 5 Population Distribution of TCA in Corks within a bale[8]
The affect of TCA on wine can only be determined after the bottle has been sealed with the cork and time has passed. The researchers performed an analysis of bottled wine for TCA to help determine if the knowing the releasable TCA level of the cork can help determine the affects it will have on the wine after the wine bottle has been sealed with the cork. The analysis showed that there was a high correlation to the releasable TCA measured in the cork before it was placed on the bottle to the wine. As an average, the test bottles contained TCA after 14 months at a level that was roughly half the level of Releasable TCA measured by individual cork soaks. This is displayed in Figure 6.
Figure 6 Soaked vs. Bottled Wine [9]
Determining the releasable TCA in a cork can be determined within 24 hours but determining the TCA level in the wine takes a longer time. Bottles from combined test bales showed TCA in the bottle at a ratio of slightly less than 15% after 30 days. This ratio increased over time. At the conclusion of the test , bottled wines included TCA at a rate of roughly half of the releasable TCA measured in their respective corks. Figure 7 shows the TCA level of a bottled wine over a duration of fourteen months.
Figure 7 Releasable TCA vs. Storage Duration [10]
Graphs of the results in the project were provided but that raw data was not available. Because of this we have to assume that the graphs are representative of the actual data. The project was successful in that cork manufactures would able to predict the amount of TCA levels that would be found in a wine bottle as a function of time and would be able to better set the quality and price. Along with the chemical analysis, other testing methods could be used to reinforce the quality. Visual inspection could be used to make sure the cork has a certain consistent feature and also sensory analysis. The sensory analysis, though less sensitive to TCA levels, will be able to be a final determination for acceptance or rejection of a cork lot.
In conclusion the project determined that cork soak can be used to determine the releasable TCA in a cork which would be a tool for determining what the TCA in wine would be if a particular cork is used. Because of tests like these manufactures are able to determine the exact level of TCA in a given cork and reject it if does not meet the requirement. This process along with a good sampling method, is a framework for quality control and continual improvement methods which are among the reasons why the percent of TCA cases decrease each year.
REFERENCES
Montgomery, Douglas C. Introduction to Statistical Quality Control. 5th Edition. John Wiley & Sons, 2005
ETS Laboratories, Chemical Analysis of TCA As a Quality Control Tool For Natural Corks
Wikepedia The Free Encyclopedia. “Cork Taint”. 2 December 2008, <http://en.wikipedia.org/wiki/Cork_taint>
Caputo, Tina “Portugese Cork industry unites.(to fight cork taint in wines)”. High Beam Research. 1 September 2002 <http://www.highbeam.com/doc/1G1-92043587.html>
Frederic Douglas . “GC/MS Analysis” Scientific Testimony an online Journal <http://www.scientific.org/tutorials/articles/gcms.html>
Figure 1 TCA Detected in 100 Cork Soaks from Four Bales 3
Figure 2 Total TCA vs. Soak TCA 4
Figure 3 TCA levels with repeated soaks 5
Figure 4 TCA detection vs Soak Volume 5
Figure 5 Population Distribution of TCA in Corks within a bale 6
Figure 6 Soaked vs. Bottled Wine 7
Figure 7 Releasable TCA vs. Storage Duration 8
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[1] “Cork Taint”. http://en.wikipedia.org/wiki/Cork_taint
[2]ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[3] Portugese Cork industry unites.(to fight cork taint in wines . http://www.highbeam.com/doc/1G1-92043587.html
[4] “GC/MS Analysis” http://www.scientific.org/tutorials/articles/gcms.html
[5] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[6] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[7] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[8] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[9] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”
[10] ETS Laboratories “Chemical Analysis of TCA as a quality control tool for Natural Corks”