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I am curious, what makes you believe that it is time to change some corks on old VP?

And when it happens, how is it done?

I never think it is time to change old corks. If the cork has failed or looks like it might then drink the bottle. Old corks, especially the long ones, are like parrots in that they live forever mostly. I think old fragile wines really don't like being recorked. I wonder if they ever get over it.

I also think replacing a cork is a last resort. There is a thread on the forum about replacing the wax seal. If I had a leaker that I wanted to keep rather than drink I would try that first.

Are you saying that some corks in VP bottles are longer than in regular bottles?

Does it mean that nobody here ever changed the corks of their VP?

Some re-corking is definitely done; for example, Ferreira re-cork their 1815s every 30 years. Whitwhams in the UK have recorked many bottles, as have Wylie fine wines. How they decide when, I cannot say; I would guess along the lines of either when they find a bottle leaking in a case of wine and decide to re-cork the batch.

That's Interesting!! I wish I could know more about it

mapmap wrote: ↑06:29 Sat 04 Feb 2017 Are you saying that some corks in VP bottles are longer than in regular bottles?

It seems to me that old bottles (and some new ones) have longer corks. I wish I had some to hand so I could show you pictures, but I would guess that the average bottle of plonk has a cork of about 5cm and I think that I have seen corks at least 1 or 2cm longer. It is not just port, high quality Bordeaux (Claret) are often longer.

mapmap wrote: ↑23:11 Wed 01 Feb 2017 And when it happens, how is it done?

I have never seen it done, I assume they simply remove the old cork and put in another, using a corking machine or by hand with a 'flogger' as I believe it is called. I think Chateau Latour and Penfolds Grange used to offer a recorking service to customers every 25 years if they wished. In this case they would also check the quality of the wine and top it up before recorking. Older ports stored in the shippers lodges in Oporto are often recorked prior to shipment abroad, I have had Taylor 1985 which has clearly been recorked (you could tell by how dark and wine stained the cork is) and I have some Cockburn 77 which seems to have been recorked.

The length of the cork is more a factor of the bottles internal neck diameter, length, how it's shaped, and the quality of the cork. Longer isn't always better and shorter isn't always worse.

And surely recorking must double the chances of the wine being corked.

You think so? I'd be curious to have that hypothesis confirmed LGTrotter, thought Interesting!

I researched this extensively a decade ago and ended up concluding that it is generally a bad idea.

Part of the problem is getting old port corks out without breaking them - unless you re-cork very frequently, which must increase the risk of a corked bottle, this is hard to do.

What I did succeed in doing was to perfect the art of over-waxing old bottles to the extent of achieving an excellent seal even when the original cork was failing and starting to leak badly. Using Method 2 below, ullage rates can be brought below 0.4g p.a. - or to put it another way, a seal good enough for only about 5% ullage over 100 years.

Here is my updated advice on the subject:

Method 1

Secure a supply of traditional sealing wax, melt carefully, dip your cleaned bottle neck quickly, make a half turn of the bottle after withdrawing from the wax and then plunge into cold water. This is the commercial way of waxing because it is quick. You can find YouTube videos demonstrating the method.

Downside: You will probably find it takes time, and a lot of mess, before you get it right. The resulting wax coat is extremely brittle, and the seal tends to be imperfect.

Method 2

Secure a supply of the wax sold as bottle sealing wax by British Wax (http://www.britishwax.com) This is a more rubbery wax that makes a superb seal, which I've been using for nearly ten years. The wax is usually shipped in slabs of about half a kilo or so, which are a bit awkward. I have recast my stock into soap moulds to make them easier to handle.

- I melt the wax in a one pint stove enamel camping mug which I place in a saucepan into which I've placed a little sunflower oil to transfer the heat. Heat the wax slowly and carefully, not leaving it unattended - hot wax burns readily.. Putting a piece of aluminium foil over the top of the mug speeds the process. You want the wax to be just over it's melting point, too hot and it becomes too fluid, with not enough adhering to the bottle.

- Clean the top of the bottle carefully. I start by using an old toothbrush, which I dip into hydrogen peroxide - this both sterilises the surface, and froths on contact with cork, lifting old grime as it does so. You can easily buy 11% or 12% food grade hydrogen peroxide on eBay. This is the only chemical I trust not to taint the content of the bottle. If old wax is still adhering well enough to withstand the rigours of the toothbrush, I leave it in situ and wax over it. If the bottle has a selo, remove it entirely or pare it back with a razor blade so it cannot act as a wick and spoil the seal.

- After rinsing, I dry the top of bottle with a paper towel, before degreasing the glass of the neck with a paper towel well soaked in acetone. The evaporation of the acetone also chills the glass, deterring a phenomenon on leaky bottles whereby the heat of the hot wax drives fluid out of the cork, creating a small 'blow hole' in the new wax. The degreasing is important to obtain a good seal - even the grease from your fingerprints can spoil the seal, so do not touch the neck after you've cleaned it.

- If the bottle has a depressed cork, take an ordinary white wax candle (not a scented one!) and drip wax to fill the void. If you fill with the sealing wax it can make opening the bottle much harder in the future.

- If the bottle has been leaking badly, use a disposable artists paintbrush and paint wax over the top of the bottle before dipping.

- If the bottle has an old fragile label, wrap it in clingfilm to protect it from the next stage.

- Dip the neck of the bottle into the wax and immediately remove it, holding the bottle at 45 degrees over the wax pot, spinning it in your hands as the excess wax drains off. When this has reduced to fine stream, start slowly raising the bottle to the vertical, spinning all the while.

- Next, check the new wax for air bubbles. If found, light a match and hold it close to the wax. This will pop the bubble, and dancing the flame next to the wax will usually cause the resultant void to heal over.

- If you make a mess of the operation, you can either cut the new wax off and start again, or make a second dip. Use acetone in liberal quantity to chill and harden the wax, before dipping again.

- Don’t forget that acetone is highly flammable..!

mapmap wrote: ↑02:56 Wed 08 Feb 2017 You think so? I'd be curious to have that hypothesis confirmed LGTrotter, thought Interesting!

My hypothesis being that if you have, say, a 1 in 20 chance of a cork being tainted in the general cork population then if you have put 2 corks in one bottle during its lifetime then you have a 1 in 10 chance of the bottle being corked.

LGTrotter wrote: ↑19:35 Fri 24 Feb 2017

mapmap wrote: ↑02:56 Wed 08 Feb 2017 You think so? I'd be curious to have that hypothesis confirmed LGTrotter, thought Interesting!

My hypothesis being that if you have, say, a 1 in 20 chance of a cork being tainted in the general cork population then if you have put 2 corks in one bottle during its lifetime then you have a 1 in 10 chance of the bottle being corked.

This is something I've never fully understood. Is there anything that can be done to reduce the potential for a cork to be tainted with TCA? Irradiation? Dipping in some kind of chemical? Something else? I had thought that TCA taint was possible without a cork. Is a cork an amplifier for potential TCA? A bit like the way rice is a breeding ground for bacteria due to the surface area?

Very interesting reply SIR Uncle Tom! Merci beaucoup!

LGTrotter wrote: ↑19:35 Fri 24 Feb 2017

mapmap wrote: ↑02:56 Wed 08 Feb 2017 You think so? I'd be curious to have that hypothesis confirmed LGTrotter, thought Interesting!

My hypothesis being that if you have, say, a 1 in 20 chance of a cork being tainted in the general cork population then if you have put 2 corks in one bottle during its lifetime then you have a 1 in 10 chance of the bottle being corked.

I don't think that is statistically true.

Each time you roll a dice you have a one in six chance of throwing a six. The next time you roll it you have a one in six chance of throwing a six. And the next time, and the next time and the next time. They are all independent of one another.

Not winning the lottery this week does not increase your chances of winning it next week

Derek might have misread Owen. Two corks, each with an independent 1-in-20 chance of being bad, gives an (approx†) 1-in-10 chance that the wine has become damaged.

† More pedantically 1−(19/20)² = 39/400 = 9¾%, but given the inaccuracy in the 1-in-20 estimate, 10% isn’t really wrong.

jdaw1 wrote: ↑21:23 Sat 25 Feb 2017 Derek might have misread Owen. Two corks, each with an independent 1-in-20 chance of being bad, gives an (approx†) 1-in-10 chance that the wine has become damaged.

† More pedantically 1−(19/20)² = 39/400 = 9¾%, but given the inaccuracy in the 1-in-20 estimate, 10% isn’t really wrong.

Derek remains unconvinced.

If both corks were from the same 1980s dodgy source then perhaps that logic works. One from the 1980s and one from today's more reliable and stringently tested sources would not give the same result.

And I still think the chance of it happening each time a cork is put in a bottle is independent of whether or not that bottle has had another cork in it.

DRT wrote: ↑08:20 Sun 26 Feb 2017If both corks were from the same 1980s dodgy source then perhaps that logic works. One from the 1980s and one from today's more reliable and stringently tested sources would not give the same result.

Agreed. What do you think was the probability then? What do you think is the probability now?

jdaw1 wrote: ↑11:24 Sun 26 Feb 2017

DRT wrote: ↑08:20 Sun 26 Feb 2017If both corks were from the same 1980s dodgy source then perhaps that logic works. One from the 1980s and one from today's more reliable and stringently tested sources would not give the same result.

Agreed. What do you think was the probability then? What do you think is the probability now?

Then? 1:20 (assuming the ratio claimed above is true)

Today? whatever today's ratio of tainted v untainted new corks is.

When tossed a coin has a 50% chance of landing heads-up. If you toss 19 heads in a row what are the odds that the 20th will be heads?

DRT wrote: ↑13:12 Sun 26 Feb 2017When tossed a coin has a 50% chance of landing heads-up. If you toss 19 heads in a row what are the odds that the 20th will be heads?

If you can toss 19 heads in a row, then I think you've probably got a double-headed coin

We seem to be straying into the world of alternative facts. It is true that each toss of the coin or putting in of a cork is independent of the last, however this is irrelevant to the point I am making. If you toss a coin twice or use 2 corks you double the chances of getting a head or a corked cork (with due deference to Julian's mild mathematical tweaking, for which I thank him).

My use of 1 in 20 was a guess for illustrative purposes. I remember it being suggested that it depended on whose research you looked at as to the ratio of corked bottles. Stelvin and the like reporting corked wines as being more common than 1 in 10 while the cork manufacturers putting it at nearer 1 in 20. But I cannot remember exactly.

Being nearly immune to cork taint I know that I am on shaky ground but I think corked wines turn up in my life with the same regularity as they ever did in any of the previous decades.

DRT wrote: ↑13:12 Sun 26 Feb 2017When tossed a coin has a 50% chance of landing heads-up. If you toss 19 heads in a row what are the odds that the 20th will be heads?

But it only takes one "heads" for the bottle to become corked.

If you toss two coins, what are the chances that you will get at least one head?

One chance to get TT.
One chance to get HT.
One chance to get TH.
One chance to get HH.

So your chances of getting at least one head are 3 in 4.

The same applies to corking bottles, which is what Julian's math demonstrated.

Now... there's another possibility. Is your argument that the person re-corking the bottle would not continue if, during the process of re-corking, it became obvious that the Port was already corked? In that case, then you are correct because the possible effects of the first cork are removed from the equation. (Assuming 100% detection. Guaranteeing that I'm not doing the re-corking.)

LGTrotter wrote: ↑18:44 Sun 26 Feb 2017 If you toss a coin twice or use 2 corks you double the chances of getting a head or a corked cork

That is absolutely not true. The second toss of a coin is completely unaffected by the previous toss. They are independent actions and outcomes, each with a 50:50 chance.

Corks are different depending on the circumstances of the experiment.

If the average rate of taint is 1 in 20 and you have 20 corks that are precisely average quality then with each re-corking from the same batch the chances increase. First corking is 1/20, second 1/19, third 1/18, etc. (unless one of those is the tainted one)

How many times is it likely that someone will re-cork a bottle using the same batch of corks as the original corking? Yes. Never. So each time you cork a bottle you are dealing with a new 1/20 chance. The first corking is unconnected to the second, just like throwing a dice.

Glenn E. wrote: ↑00:54 Mon 27 Feb 2017

DRT wrote: ↑13:12 Sun 26 Feb 2017When tossed a coin has a 50% chance of landing heads-up. If you toss 19 heads in a row what are the odds that the 20th will be heads?

But it only takes one "heads" for the bottle to become corked.

If you toss two coins, what are the chances that you will get at least one head?

One chance to get TT.
One chance to get HT.
One chance to get TH.
One chance to get HH.

So your chances of getting at least one head are 3 in 4.

You have fallen into the trap of using the same batch of 20 corks. The dice are not being thrown at the same time so your predicted outcomes are incorrect.

DRT wrote: ↑21:38 Tue 28 Feb 2017

Glenn E. wrote: ↑00:54 Mon 27 Feb 2017

DRT wrote: ↑13:12 Sun 26 Feb 2017When tossed a coin has a 50% chance of landing heads-up. If you toss 19 heads in a row what are the odds that the 20th will be heads?

But it only takes one "heads" for the bottle to become corked.

If you toss two coins, what are the chances that you will get at least one head?

One chance to get TT.
One chance to get HT.
One chance to get TH.
One chance to get HH.

So your chances of getting at least one head are 3 in 4.

You have fallen into the trap of using the same batch of 20 corks. The dice are not being thrown at the same time so your predicted outcomes are incorrect.

Nope, in fact the math we're using specifically abstracts away from that exact thing.

When you re-cork a bottle, you are introducing a second chance to cause the bottle to be corked. That's what my coin toss example demonstrates. If either coin comes up heads, your bottle is corked.

Now you can quibble that the first coin has a greater chance of being heads than the second, because technology has improved over time and new corks have a much lower chance of causing a wine to become corked, but you cannot ignore the first cork which is what you're doing. If the first cork causes the wine to be corked, it doesn't matter if the second one is pristine or not - your wine is still corked.

What you're arguing is the chance that the second cork will cause the bottle to become infected, which isn't sufficient.

DRT wrote: ↑21:27 Tue 28 Feb 2017If the average rate of taint is 1 in 20 and you have 20 corks that are precisely average quality then with each re-corking from the same batch the chances increase. First corking is 1/20, second 1/19, third 1/18, etc. (unless one of those is the tainted one)

Incorrect. You're describing the wrong experiment. You're not using average corks, you're using a set of 20 corks in which one is guaranteed to be flawed. Because in your experiment, on the 20th cork there's a 1/1 chance of infecting the bottle (assuming you make it that far), while in reality there's about a 36% chance that a set of 20 bottles will be pristine even if each cork as a 1/20 chance of being tainted.

The correct way to run the experiment is:

(19/20) * (19/20) * (19/20) * ... etc., for as many times as you want to re-cork the bottle.

19/20 is the chance of a cork being clean. And every single (re-)corking must use a clean cork or your bottle will become tainted, so it's (19/20)^X where X is the number of times you want to (re-)cork the bottle. (Don't forget to include the original cork.)

(19/20)^20 is ~36% chance that the bottle is still clean after 19 recorkings (20 total counting the original cork).

(19/20)^2 is 90.25% chance that the bottle is still clean after 1 recorking (2 total corks). Or as Julian put it, a 9.75% chance that the wine as become damaged.

Put another way:

The chance of any given cork causing the wine to become tainted is independent, but the chance of the wine becoming tainted is cumulative because it doesn't matter which cork causes the problem... corked is corked.

Does anyone know where Phil's thread about port corks being branded on the ends is? This bottle of Senhora do Convento had a cork branded on the end with the date. Until the dog ate it.

Sorry to interrupt. Found it. Why can't you delete posts anymore?

Everything Glenn just said, I knew, but just couldn't explain. Honest.

Glenn E. wrote: ↑22:18 Tue 28 Feb 2017(19/20)^20 is ~36% chance that the bottle is still clean after 19 recorkings (20 total counting the original cork)

So how does that equate to the original assertion that re-corking a bottle once doubles the chances of it being corked?

I was taught that the best way to get your head round questions of probability was not to dwell on the chances of something happening, but on the chances of it not happening.

If you play Russian roulette with a six chamber revolver once, you have a 5/6 chance of survival. Play it twice and you have a 5/6 x 5/6 chance, or 25/36 chance or survival - which is slightly greater than the 2/3 chance (or 24/36) one instinctively assumes.

Similarly if you play it six times you are not assuredly dead - the chance of survival is 15625/46656 - which is very close to 1 in 3

DRT wrote: ↑21:55 Wed 01 Mar 2017

Glenn E. wrote: ↑22:18 Tue 28 Feb 2017(19/20)^20 is ~36% chance that the bottle is still clean after 19 recorkings (20 total counting the original cork)

So how does that equate to the original assertion that re-corking a bottle once doubles the chances of it being corked?

Round 1. 20 good bottles + 19 good corks + 1 tainted cork gives 19 good bottles + 1 corked bottle

Round 2. 19 good bottles + 1 corked bottle + 19 good corks + 1 tainted cork only gives 19 good bottles and 1 corked bottle if you are lucky enough to put the tainted cork in the corked bottle, else you get 18 good bottles, 1 newly corked bottle, and 1 old corked bottle with a new good cork in it.

DRT wrote:

Glenn E. wrote: ↑22:18 Tue 28 Feb 2017(19/20)^20 is ~36% chance that the bottle is still clean after 19 recorkings (20 total counting the original cork)

So how does that equate to the original assertion that re-corking a bottle once doubles the chances of it being corked?

(19/20)^2 gives a roughly 10% chance that the bottle is corked (90% chance that it is still clean), which is double the chance that it was corked with its original stopper.

Ergo, re-corking a bottle roughly doubles the chance of it being corked.

Note that "double the chance" is only roughly accurate because the chance of any given bottle being corked is so low to start with. If the chance were 50%, like flipping a coin, then re-corking a bottle would only increase its chances of being corked by 50%. (From 50% to 75%.)

DaveRL wrote: ↑13:12 Thu 02 Mar 2017Round 1. 20 good bottles + 19 good corks + 1 tainted cork gives 19 good bottles + 1 corked bottle

That is precisely the problem with this debate. The hypothesis being put forward relies on a captive batch of corks with a 1/20 taint rate.

My point is that because the first corking and the second corking are separated by many years or decades there is no connection between the corks and they will have vastly different taint rates. Each re-corking is an entirely independent action which has a singular chance of resulting in a corked bottle that is at the rate that is relevant to the batch of corks being used for that event.

Put another way - If you tossed a Farthing in 1945 and it landed on tails, what is the probability of a Trump Dollar landing on heads in 2017?

DRT wrote:Put another way - If you tossed a Farthing in 1945 and it landed on tails, what is the probability of a Trump Dollar landing on heads in 2017?

Except that isn't the question.

First, though, you are correct about DaveRL's scenario. His assumes a fixed set of non-independent corks which is not correct. The math I have used (as has jdaw1) assumes independent corks.

The correct time-spanning question is no different than what I asked before: what is the chance that you will get at least one head if you flip two coins?

The answer is 75%. Not 50%. 50% assumes you already know that the first coin was tails, but with a bottle of wine you do not know that.

Thus the formula I gave you.

Put another way: we will split the cost of a case of Port. To choose who gets each bottle, we will flip 2 coins. If either coin comes up heads, I get the bottle. If both are tails, you get the bottle.

Math say I will get 9 and you will get 3, on average. Mine are the corked bottles, though, so you shouldn't care.

If: (a) the first cork used has a 1 in N chance of causing the bottle to be corked, and (b) the second cork used has a 1 in M chance of causing the bottle to be corked, then the chance of the bottle being corked is 1-(((N-1)/N )*((M-1)/M)) with additional brackets used for the hard-of-priority. This can be continued as needed. N and M need not, but might be the same. Per earliest posts, with N=M=20, the probability of being corked is 9.75%.

flash_uk wrote: ↑08:14 Fri 03 Mar 2017 Who's on first?

Very funny.

Ha ha. I just knew I shouldn't get involved in a maths question.

Old Bridge wrote: ↑15:39 Fri 03 Mar 2017

flash_uk wrote: ↑08:14 Fri 03 Mar 2017 Who's on first?

Very funny.

+1

flash_uk wrote: ↑08:14 Fri 03 Mar 2017 Who's on first?

I'm going to concede and withdraw on this basis that now is not a good time in history to be compared to a mildly racist New Yorker

Ok - I get it. I have been thinking of the corks when I should have been focusing on the bottle. Each cork has the same chance, the bottle is being subjected to multiple chances.

DRT wrote: ↑19:24 Fri 03 Mar 2017Ok - I get it. I have been thinking of the corks when I should have been focusing on the bottle. Each cork has the same chance, the bottle is being subjected to multiple chances.

Exactly!

Now go have some Port. I'm drinking 1995 Souza at the moment.