Beer Analysis at VinlabSeptember 19, 2016
Vinlab Report: Thiol Stability During ProcessingOctober 25, 2016
We have received a number of queries recently about TCA analysis: what it is; how to test for it; and also some questions about the more specific details of the method and results.
BACKGROUND: WHAT ARE THE HALOANISOLES AND HALOPHENOLS?
TCA and the haloanisoles:
- TCA (2,4,6-trichloroanisole) is one of a group of compounds called the haloanisoles. It is the main compound responsible for cork taint in wine.
- Other compounds that may contribute to cork taint: TeCA (2,3,4,6-tetrachloroanisole); PCA (2,3,4,5,6-pentachloroanisole); TBA (2,4,6-tribromoanisole).
- The haloanisoles are formed by the action of mould on halophenol precursors.
- The halophenols are formed when chlorine/bromine-containing products react with phenols in corks and in other areas of the winery environment.
- Chlorine-containing products were used in the past to treat corks. TCP (2,4,6-trichlorophenol) is formed when chlorine reacts with phenols in the corks.
- The halophenol precursors, including TCP, TeCP (2,3,4,6-tetrachlorophenol), PCP (2,3,4,5,6-pentachlorophenol) and TBP (2,4,6-tribromophenol), may be found at many different areas in the winery environment (see below).
TCA AND HALOANISOLES FROM CORKS:
- The presence of cork taint in wine is usually, but not always, attributed to contaminated corks.
- Significant between-bottle variation may indicate that contamination is probably from corks.
- If wine tests negative for TCA, TeCA and PCA before bottling, then the contamination is likely to have come from the corks.
- TCA levels below 0.3-0.5 ng/L in wine before bottling indicate that the cellared wine is not contaminated.
- TCA levels in corks soaks up to 1 ng/L generally indicate that the batch of corks is acceptable. Note that winemakers and cork suppliers may have their own specifications.
TCA AND HALOANISOLES FROM THE CELLAR:
- Haloanisoles may also contaminate wine from various places in the winery environment.
- It is important to note that very low levels of TCA in the winery environment can contaminate cellared wine. Low levels of TCA correspond with very small amounts of chlorine where mould is present.
- Testing TCA before bottling will indicate any TCA contamination that doesn’t come from corks.
- Higher levels of TeCA and PCA in bottled wines may indicate that contamination occurred in the cellar.
- Where TCA is suspected to have come from the cellar, a thorough investigation should be conducted to find the source of contamination.
- There are a number of different ways that wines may become contaminated in the cellar. TCA and the other haloanisoles are very volatile and very low levels in the air can contaminate wine, empty storage containers, corks and other bottling materials, oak products, bentonite, filtration equipment etc.
- Winery water: Municipal water is often treated with chlorine. This can be a source of TCA and other haloanisoles where moulds are allowed to grow. Carbon filters may be used to remove chlorine.
- Resins, plastics and treated wood (doors, beams, plywood panels, pallets etc) in the cellar: These are often treated with, or contain, chlorine or bromine-containing products. Where mould is allowed to grow, TCA, TeCA, PCA and TBA may be produced.
- Chlorine and bromine-containing cleaning products: In the presence of mould, any chlorine residue from cleaning products may result in the production of haloanisoles. Chlorine and bromine-containing cleaning products should be avoided.
- Cork taint compounds have very low sensory thresholds and if wine comes into contact with them, it will become contaminated very rapidly.
- The sensory threshold for TCA is between 2-5 ng/L.
- The sensory threshold for TBA is 3-4 ng/L and for TeCA is 10-15 ng/L.
- The sensory threshold for PCA is much higher than levels found normally in contaminated wine.
TESTING FOR TCA:
- Corks: Potential contamination of new corks may be tested on cork soaks. A representative sample of 50 corks is soaked in a wine-like solution. Contaminated corks will release TCA and the other haloanisoles into the solution. The solution is then analysed.
- Wines: wine samples are analysed directly.
- The Vinlab method for testing TCA is ISO17025 accredited.
- Our detection limit is 0.3 ng/L.
- In addition to TCA, we also measure the other haloanisoles as part of the analysis.
- We perform regular interlaboratory checks with leading wine laboratories in California (ETS) and France (Excell).
- The method uses a technique called headspace SPME (solid-phase microextraction). After sample preparation, the volatile anisoles are adsorbed on a fibre and then analysed.
- Calibrations are done by adding known levels of the compounds to a wine-like solution.
- We have numerous other checks and balances in place for ensuring accuracy, including performing spikes where necessary, analysing controls and analysing blanks.