Fight against TCA
The investment in the quality of the stoppers sub-sector had the objective of eradicating TCA, a chemical compound that is related to sensory deviations that cause the mould smell/taste in wine. There are several projects in this field (link to extraction methods, prevention and control of TCA) besides the Systecode certification and implementation of the International Code of Cork Stopper Manufacturing Practices.
What is TCA?
It is a chemical compound commonly present in nature that can be found in wood, wine, water, soil, fruits and vegetables and also in cork. It is exogenous to the wine product, the wood and cork stopper, but if it is present in the atmosphere and comes into contact with the casks, corks or wine, it may easily be absorbed. TCA may form directly in some of these products if they are contaminated with chlorophenols, which are the principal precursors of TCA. For the formation of chlorophenols, a substance which contains phenol has to come into contact with a source of chlorine. If, for example, a cork stopper is washed with chlorine, the possible appearance of chlorophenols is potentialized.
The cork industry banned this practice in the cork stopper washing process more than 15 years ago. The International Code of Cork Stopper Manufacturing Practices specifically prohibits the use of chlorine and also any means containing this compound at any stage of stopper fabrication. Stoppers are currently washed with hydrogen peroxide as the preferred means of disinfecting and bleaching.
TCA is a compound that does not cause any problem to human health and its limit of perception varies according to the consumer, the wine, the occasion on which the wine is consumed, among other factors.
Extraction, prevention, and control of TCA
There are, in addition to the measures proposed in the ICCSMP, other processes for the eradication, prevention and control of TCA.
New boiling systems – These processes are dynamic systems where water is circulating continuously and it is treated before it re-enters the boiling system. These systems allow for uniform boiling of all of the planks at high temperatures.
Controlled steam distillation – The steam distillation of cork products, particularly granular products to be used in champagne and specialised stoppers, is a highly effective process for the extraction of TCA. The volatility of TCA allows its distillation in the vapour stream.
Volatilization by distillation in controlled temperature and humidity – This process takes advantage of the fact that TCA has a volatilization temperature of 60ºC. In a constantly renewed atmosphere of high relative humidity and temperatures above 60°C a significant extraction of TCA from cork stoppers is achieved. This process is used in natural stoppers as it is not only highly effective at reducing TCA levels, but also does not cause deformation of those stoppers.
Volatilization by distillation in the gaseous phase of adjusted polarity, under controlled temperature and humidity – This process introduces the use of ethanol in the distillation phase, based on the principles of distillation and steam distillation and looking for a polarity adjusted to the extraction of molecules such as TCA. The process allows for the effective treatment of natural cork stoppers, preserving all of their physical and mechanical properties through the optimized combination of temperatures close to 60°C, concentration of ethanol in the steam phase, and continuous inflow of hot air.
Extraction with CO2 in the supercritical state – This process subjects granulated cork to a stream of CO2 in supercritical state to remove the TCA and possibly other volatile compounds from cork products.
Ionisation – The substantial reduction of the microbial load contributed significantly to the prevention of TCA forming. A sterilizing process of different materials called ionization can be used with cork products, contributing to their microbial decontamination.
Microwaves – The system works by vibration of the bonds through electromagnetic waves, which causes the molecules to generate heat internally. This increase of internal temperature promotes the phenomena of evaporation, namely water present in the matter, allowing co-volatilisation of metabolites by the action of steam.
Symbios – is a process developed by the Cork Technological Centre (CTCOR) (link to www.ctcor.com) which impedes the formation of chloroanisoles in cork, notably TCA. It is a preventive biological process, which brings about the development of benign microorganisms, which occur naturally in cork, to the detriment of microbiological species with potential formation of undesirable metabolites and the inhibition of biosynthesis of chloroanisoles during the transformation stages of cork.
As an additional advantage, during the boiling phase of the cork, this process brings about extraction of water soluble materials in the cork, such as soil and polyphenols (with potential negative impact on contact with drinks).
Enzyme action – Trichlorophenol is the principal precursor of TCA by fungal metoxilation of its OH group . Some enzymes are able to polymerize the compounds, including chlorophenol, making them unavailable to the methoxylation referred to above.
Gas chromatography (SPME-GC/MS, SPME-GC/ECD) (isso 20752) – The Cork Quality Council), of the USA has developed a research project using analysis by SPME-GC/MS which allowed technologically complex and very sensitive equipment to be used in the quantification of TCA in batches of cork. It is the combination of the solid phase micro-extraction technique (SPME) and gas chromatography (GC) preferentially adopting detection by mass spectrometry (MS). The use of other highly sensitive detection systems is also feasible, such as electrons capture (ECD).
During the first research phase, new analytical tools were identified to replace the sensorial method using a chemical analysis process. The researchers said “the objective was to develop a qualitative and non-destructive test, while at the same time allowing for improvement in the level of sensitivity and reliability.”
The second and third phase of the research ended with the definition of the concept of migratable TCA resulting from laboratory analysis of the level of TCA of cork stoppers and the correlation with their performance in wine bottles. Information was needed on the dynamics of transfer of the TCA to understand what are the conditions necessary for a representative analysis.
The fourth phase sought to apply the laboratory methodology to a commercially viable quality control tool, and this gave rise to the current ISO 20752.
This year (2015), the CQC has conducted 30,000 analyses which show the reduction of levels of TCA in the region of 95% compared with 2001. Another conclusion of this study is that 91% of the samples have TCA below 1ppt (1.0 ng/l).
.Sensory analysis (isso/PRF 22308) – For many years sensorial analysis has contributed to quality control for cork stoppers. The analytical procedure is expressed in the ISO/PRF 22308 standard and has the advantage of not only describing the methodology to identify the aromas of mould, but also other aromas which may be present in the cork stoppers.
The curative, preventive, and control processes of TCA in cork products have contributed significantly to the qualitative improvement of these products and to improving their image with users, consumers and wine critics.
Some examples of this are given in the following testimonies: