Who assumes the risk of corked bottles?

[Jeff Grossman]

Does it stick to teflon?

 

[MLipton]

originally posted by nigel groundwater:

Mark, yes it helps to explain your correction further for which many thanks but without knowing how your TCA reaches equilibrium quickly actually quantifies in seconds?, minutes?, 10+ minutes? I still have difficulty in seeing that all the TCA molecules that are going to be available are instantly [= quickly?] in the headspace, that at low levels TCA is being masked by other aromas and that a temperature movement of 10oC has little impact on the ability to sense TCA. And might not the fact that the headspace isnt closed have some impact on the time taken to reach equilibrium and how that might affect when it is at a sufficient level to be sensed by the consumer.

I understand your desire to get a quantitative basis for this statement, but it's frankly impossible for me to provide one. First of all, factors such as the exposed surface area of the wine, the opening in the top of the glass, the volume of the headspace and the amount of TCA in the wine will all affect the answer. The problem here is that the system, being open, will never reach true equilibrium (at least in any time scale that we would care about), but rather reach an approximate equilibrium. What would we would need to compute it is a mean free path for TCA diffusion as well as the flux at the opening of the glass. My somewhat educated guess is that an approximate equilibrium in reached in a few (say, 1-5) minutes. We know that it's not an instantaneous process since all we winegeeks will furiously swirl the contents of the glass to help aerosolize its contents.

While TCA doesnt blow-off like e.g. certain SLOs, various AWRI studies have apparently shown that it will very slowly transfer to the atmosphere over extended periods. Also that it can transfer preferentially but slowly, from wine to a cork [plastic or natural] closure across an ullaged headspace over an extended period.

That makes sense and is in accord with what I say above.

Essentially Mark you are saying [Perzackly, Nigel. Spot on.] that the often reported delay in sensing TCA is not due to a progressive increase [because you say the max level is achieved quickly] in TCA molecules in the [open] headspace but is due to the gradual decrease in the products masking it even though the identity of such products is unknown.

Yes, what I suspect based on my knowledge of diffusion rates is that the TCA concentration in the headspace remains reasonably constant after the first few minutes. So the reason it becomes more noticeable would have more to do with our perception of it rather than an increase in the amount. Just as we have trouble understanding conversation amidst much ambient noise, I suspect that low level TCA taint might be harder to make its presence felt when it's one of 40 different smells hitting our olfactory apparatus. When it becomes one of 12 it is likely far easier to detect. Not being a cognitive scientist I have absolutely no actual support for that hypothesis, but it seems the most likely to me.

The constituent differences between red and white wine might indicate some masking property in red wine since studies have shown that expert panels sense TCA more readily in white than red wine. One study showed a roughly 1:2 ppt difference as judged by the ratio of ppt of TCA in white and red wine at which the same percentage of an expert panel sensed TCA at different single figure ppt.
However the masking appeared to be a fixed sensing differential between white and red rather than something relevant to this discussion that varied over time. AFAIK no specific explanation for this differential has been given.

Most interesting. I wonder if they followed it over the course of several hours?

Interestingly, the experts calling TCA in that last study were calling it when there was no TCA present over 10% of the time.

Were there any congeners present such as DCA or TBA? I find the smell of TCA rather hard to mistake, although older Chenin gives me fits that way.

You also say that since the rise of 10oC [from 15 to 25] is only a 3.5% increase [absolute zero base] it would not significantly affect the speed or increase the quantity transferred at which equilibrium is reached However it is interesting how such small increases certainly seem to have a major sensory impact on e.g. the aromatic difference between a chilled wine and one, say, only 10oC higher.

That is certainly true, Nigel. It could be that for low MW esters the effect is more pronounced owing to their low boiling points. I will look into finding some data on the temperature dependence of diffusion constants to check this out.

There have been timed studies of [closed] headspace TCA by organisations like the AWRI and others using SPME and GC-MS/GC-ECD and related techniques so I assume that the speed at which TCA occupies the headspace and equilibrium levels might be known as part of the testing protocol. In any event it would be helpful if you are able to quantify approximately the time it would take to maximise TCA in the open headspace above the wine in a glass.

Are those studies published? If so, I'll search for those data within them.

Mark Lipton

 

[MLipton]

originally posted by SFJoe:

Zero. That sucker should be so electron-poor as to be oxidatively dead. And I don't see mass quantities of LAH piling in here.

No, it's somewhat electron rich since the oxygen is a bigtime donor and the 3 Cls are weak EWGs. Still, it's not exactly screaming "reactivity" is it? Those chlorinated aromatics tend to be persistent little mofos as the world learned to its dismay.

Mark Lipton

 

[John Ritchie]

The chemistry discussion in this thread has been most interesting. Thanks for taking the time to hash this out.

 

[Ian Fitzsimmons]

Is there a good base article on TCA's makeup and reactivity?

 

[MLipton]

originally posted by Ian Fitzsimmons:
Is there a good base article on TCA's makeup and reactivity?

Wikipedia?

Mark Lipton

 

[nigel groundwater]

originally posted by MLipton:

originally posted by nigel groundwater:

Interestingly, the experts calling TCA in that last study were calling it when there was no TCA present over 10% of the time.

Were there any congeners present such as DCA or TBA? I find the smell of TCA rather hard to mistake, although older Chenin gives me fits that way.

Mark Lipton

Mark, thanks again for a swift and comprehensive response. I will consider whether I can usefully continue our original dialogue but think perhaps it has moved the discussion forward about low level TCA taint and how and when it might be perceived after a bottle is opened and glasses are poured.

I might take up our dialogue with a study group who are constantly measuring haloanisoles and their perception in relation to wine to see if they have any further comments or are able to fill in some of the gaps or areas that remain intuitive such as the type of masking agents that might be affecting the observed delays in the perception of very low level TCA. If I do I will report back on anything interesting they have to say.

As far as your question above is concerned the report referred to TCA only and the calls being made incorrectly where the wine was 'clean'. I assume that since the analysis was conducted using SPME and very sensitive GC-MS equipment [to 0.2 ppt of TCA] that 'clean' wine certainly meant no other potentially confusing products like TBA which has similar musty smell and sensitivity thresholds close to TCA or if there had been it would have been picked up and commented on.

I believe what was happening is that some of the expert panel, who obviously had different sensitivity thresholds, were detecting 'something wrong with the wine' [at what were very low ppt unless it wasnt there at all] as well as 'recognising the fault as TCA' [at significantly higher ppts when I assumed they could probably smell it at least some of the time] and the anomalies occurred when TCA was assumed to be the cause of the something wrong despite there being no link as obvious as its distinctive odour. While a 10% error doesnt sound much this was in a test where there was only one white wine and one red wine [unfortunately not specified] which had been bottled for the study in several thousand bottles with a variety of different closures which were analysed using SPME and GC-MS.

528 bottles of the 2600 were then tasted by the panel to compare the actual with the perceived level of TCA and as each bottle was tasted 2 samples were taken, sealed in individual glass capsules closed with foil caps and analysed.
The study was in batches over several months and the panel were only tasting the same 2 wines time after time and saying when they believed TCA was present.

Some of the critical factors here were (a) the panel were experts experienced in TCA detection (b) it was the same wine being tasted time after time and (c) what they were looking for was TCA.

The main anomaly was described as there was a greater than 10% chance of reporting TCA when there was none although among other data points over half the panel detected TCA when it was 1.2 ppt [white] and 2.5 ppt [red] and three quarters detected it at 2.07ppt and 3.93 ppt respectively hence the 1:2 white/red ratio I mentioned in my earlier post when commenting that TCA is apparently easier to spot in white than red wine.

Unfortunately there was no reference to what percentage of the 528 bottles were corked and therefore no way of knowing how the 10+% wrong calls translated in numbers. However if, say, a [high] 10% of the bottles were tainted and 10% of the clean bottles were incorrectly called then 9 out of every hundred bottles were being called corked when they werent and, supposing that all the corked bottles were called correctly 10 out of every 100 were correct.

So for every call they appear to have been right about half the time even if they always spotted a corked wine correctly an assumption I made for the calculation above since the report doesnt specify missed TCA calls. Of course if the corked bottles were only 5% of the total there would have been many more wrong calls that right ones.

Bearing in mind we are talking primarily about very low TCA levels [the subject of our dialogue] I concluded that there is probably quite a lot of TCA calls made, particularly by non-experts, where TCA has become the default rationale for a wine that doesnt taste right..and when it is used as a default, when that very distinctive smell never appears [as it surely didnt for those clean wines called TCA by the expert panel] it probably accounts for some of the wilder claims about a high frequency experience of TCA reported in wine forums.

I am seeking more detailed background about this study [one of 3 conducted] including my assumptions to ensure I havent misrepresented anything and will report back if anyone is interested.